ABSTRACTS BOOK
5th European Conference on Crystal Growth
9-11 September 2015
Area della Ricerca CNR, Bologna, Italy
WELCOME
Dear Colleagues,
On behalf of the Crystal Growth section of Italian Association of Crystallography (AIC) and the European Network of Crystal Growth (ENCG), we cordially welcome you to Bologna for the Fifth European Conference on Crystal Growth (ECCG5).
The aim of ECCG5 is to represent the wide variety of topics connected with Crystal Growth, with a multidisciplinary approach able to answer the demands of the society in different fields of modern life, such as microelectronics, photonics, pharmaceutical and chemical material production, healthcare and cosmetics to name few. To delivery this, the organizing team has scheduled a wide-ranging and thought-provoking program of Plenary, Keynote and Invited conference lectures. The conference also presents two poster sessions, which are rich of very attractive and stimulating presentations. The Conference has been also organized to promote the meeting of researchers coming from public and private entities and to facilitate the cooperation between academia and industry. We aspect that that the program will trigger many fruitful discussions and that this will be an enriching experience for all of us.
We express our heartfelt gratitude to the members of International Advisory Board for their qualified and wise guidance concerning the conference structure, content and speakers and to the Local Organizing Committee who have worked in very hard way to make easy many practical, and unexpected, issues associated with the conference organization. Last but not least we are very grateful to the Sponsors and Exhibitors for their significant support.
Once again we would like to thank all of you for the participation. We are honored to have all you in Bologna and we wish you an inspiring, stimulating and enjoyable meeting.
BENVENUTI!
Giuseppe Falini Andrea Zappettini
CONTENTS
Organisation Page 3
Scientific Program Arrangements Page 9
Poster Sessions Page 10
Prizes Page 11
Plenary Lectures Page 12
Meeting Timetable Page 13
Poster Presentations Page 22
ABSTRACTS Session 1 Keynotes and oral in order of presentation Page 34 Posters Page 44 Session 2 Keynotes and oral in order of presentation Page 66 Posters Page 81 Session 3 Keynotes and oral in order of presentation Page 110 Posters Page 118 Session 4 Keynotes and oral in order of presentation Page 122 Posters Page 139 Session 5 Keynotes and oral in order of presentation Page 185
Posters Page 193 Session 6 Keynotes and oral in order of presentation Page 201 Posters Page 209 Session 7 Keynotes and oral in order of presentation Page 214 Posters Page 222 Session 8 Keynotes and oral in order of presentation Page 234 Posters Page 249 Session 9 Keynotes and oral in order of presentation Page 268 Posters Page 277 Session 10 Keynotes and oral in order of presentation Page 296 Posters Page 306 Session 11 Keynotes and oral in order of presentation Page 331 Posters Page 339
ORGANISATION
Conference Chairs
Giuseppe Falini, Università di Bologna Andrea Zappettini, IMEM-CNR, Parma
International Advisory Board
Horia Alexandru Wolfram Miller Knut Deppert Jozef Novak Thierry Duffar Eivind Øvrelid Francois Dupret Katalin Polgar Roberto Fornari Stathis Polychroniadis Christiane Frank-Rotsch Vyacheslav Puzikov Katharina Fromm Bogdan Ranguelov Brian Glennon Kevin Roberts Jaime Gómez-Morales Ewa Talik Zdenek Kozisek Janis Virbulis Damir Kralj Daniel Vizman Harri Lipsanen Elias Vlieg Hans Erik Lundager Madsen Evgeny Zharikov Florinda Mendes da Costa
Scientific Committee
Liliana Braescu Josef Novak Thierry Duffar Carlos M. Pina Giuseppe Falini Bogdan Ranguelov Christiane Frank-Rotsch Kevin Roberts Peter Gille Luca Seravalli Jaime Gómez-Morales Ewa Talik Damir Kralj Alexander van Driessche Harri Lipsanen Janis Virbulis Hans Erik Lundager Madsen Andrea Zappettini Florinda Mendes da Costa Evgeny Zharikov
Organizing Committee
Davide Calestani Simona Galli Matteo Di Giosia Annalisa Guerri Simona Fermani Patrizia Rossi
Conference Secretariat (@IMEM-CNR)
Rosella Magno [email protected] Antonella Secondulfo
Congress Venue
ECCG5 Conference will be hosted by CNR Bologna Research Area, Via Gobetti 101, Bologna. The Area offers services and support to the Italian National Research Council (CNR) and the National Institute for Astrophysics (INAF) Institutes present on the site as well as to those in other cities in Emilia-Romagna. On the campus in Via Gobetti there are a total of eight Institutes belonging both to the CNR and INAF, together with the central Area Library, Conference Centre and ancillary services. The site also accommodates ASTER (regional government science and technology agency), various groups working within the framework of SPINNER projects (promoting innovation and research) and laboratories MIST E-R and PROAMBIENTE, for industrial research and technology transfer.
The Conference Centre
The striking design of the CNR Conference Centre is the work of Enzo Zacchiroli, one of Italy's most famous architects for public building projects. The complex is an integral part of the Research Area campus, and was specifically designed for scientific discussion, meetings and conferences. It boasts a high degree of functionality within an attractive and sympathetic academic environment.
How to get there If you arrive by car (from the motorway): take the Bologna Arcoveggio exit, follow the instructions for Via Gobetti, then follow the MAP because the navigation systems may lead you astray.
If you arrive by car (from the ring road - "Tangenziale"): take exit n. 5 (LAME), follow the instructions for Via Gobetti, then follow the MAP because the navigation systems may lead you astray.
If you arrive by train: the CNR is a 5-minute taxi journey from "Bologna Centrale" Railway Station: ask for "CNR, via Gobetti 101". You can also arrive by bus, see below.
If you arrive by plane: take the AEROBUS BLQ and change to the 87 bus at the "Ospedale Maggiore" bus stop, or take a taxi: the CNR is a 10-minute taxi ride (ask for "CNR, via Gobetti 101").
If you arrive by bus:
Bus n. 87 Bus n. 11A Bus n. 11C
From Autostazione to From Autostazione to From Autostazione to Palestra Rotonda CNR 12 minutes Rotonda Gobetti 18 + 8 Ippodromo 17 minutes + 7 minutes by walk minutes by walk
Timetables and details bus 87 Timetables and details bus 11
Internet Facilities
WiFi will be available.
Conference Maps
Main Lecture Theatre – Room 105
Room 215
Registration Desk It will be open on Tuesday 8th September from 17:00 followed by the Welcome Cocktail at the “Auditorium Enzo Biagi – Salaborsa” in Piazza del Nettuno 3, Bologna. The registration desk, throughout the congress, will be located on Ground Floor of the Conference Centre.
Conference Fees On-site will be available. Payments can also be done by bank transfer or paypal.
The registration fee includes: - welcome party - access to the conference hall - conference materials - coffee breaks and launches - certificate of attendance.
All participants will receive a name badge when they check in at the registration desk. This badge must be worn at all times because only registered people will be accepted in conference halls and in the catering area.
Welcome party Welcome Cocktail will take place at 18.00 at the “Auditorium Enzo Biagi – Salaborsa” in Piazza del Nettuno 3, Bologna. In the basement of Salaborsa is located the Auditorium.
How to get here: by bus: lines and timetables on the website www.tper.it by car: located in restricted traffic zone ZTL. Ring road exits n. 11/11bis-12 direction city center.
Entrance
Coffee Breaks and Lunch Coffee breaks and lunch will be served in the Conference Venue. Delegates must wear their badges in order to have access to the catering area.
Social Dinner A social dinner has been organized on September 10, 2015 in Palazzo Gnudi. This former palace dating from the first half of the XIV Century is now a prestigious and perfectly equipped to stage cultural events, lectures and conferences of various kinds. Located in Bologna, via Riva di Reno 75/77, it is a historical building of the neoclassical style and it belonged to the family Gnudi for centuries.
How to get here: By bus: lines and timetables on the website (www.tper.it) By car: located in restricted traffic zone ZTL. Ring road exit 5 direction city center.
SCIENTIFIC PROGRAM ARRANGEMENTS
SESSION LIST Session 1: Fundamentals - Nucleation and Growth Kinetics Chair: Hans Erik Lundager Madsen
Session 2: Theory and Modeling Chair: Liliana Braescu
Session 3: Product and Process Design of Pharmaceuticals and Fine Chemicals Chair: Kevin Roberts
Session 4: Bulk Crystal Growth Chairs: Janis Virbulis, Ewa Talik
Session 5: Advance in crystal growth technology Chairs: Evgeny Zharikov, Christiane Frank-Rotsch
Session 6: Mesocrystals and Nonclassical Crystallisation / Growth of Biological Materials and Biologically-Controlled Growth Chairs: Damir Kralj, Jaime Gómez Morales
Session 7: In-situ Monitoring / Control of Crystal Growth Processes / Crystal morphology Chairs: Alexander van Driessche, Carlos M. Pina
Session 8: Epitaxial Growth - Crystal growth interfaces Chairs: Josef Novak, Luca Seravalli
Session 9: Fundamentals - Structural Defects and their characterization in Crystalline Materials Chairs: Thierry Duffar, Bogdan Ranguelov
Session 10: Nanostructures & Nanoporous Crystals Chair: Florinda Costa
Session 11: Novel materials and structures Chairs: Peter Gille, Harri Lipsanen
POSTER SESSIONS
Poster Presentation Guideline:
1) The poster displaying space is 95 cm wide by 115 cm high. 2) Display your poster by yourself in the morning of your poster session in the designated panel; your presentation number will be indicated on the panel. Please use pushpins prepared to put up your presentation on the poster board. 3) Remove your poster at the evening of your poster session. Materials left on the poster boards after the removal deadlines will be thrown away.
Poster session A: Date: 9-11-2015, 13:45 – 15:45 Posters of the scientific sessions: Session 1: Fundamentals - Nucleation and Growth Kinetics Session 2: Theory and Modeling Session 3: Product and Process Design of Pharmaceuticals and Fine Chemicals Session 4: Bulk Crystal Growth Session 5: Advance in crystal growth technology
Poster session B: Date: 10-11-2015, 13:30 – 15:30 Posters of the scientific sessions: Session 6: Mesocrystals and Nonclassical Crystallisation / Growth of Biological Materials and Biologically- Controlled Growth Session 7: In-situ Monitoring / Control of Crystal Growth Processes / Crystal morphology Session 8: Epitaxial Growth - Crystal growth interfaces Session 9: Fundamentals - Structural Defects and their characterization in Crystalline Materials Session 10: Nanostructures & Nanoporous Crystals Session 11: Novel materials and structures
PRIZES
Several awards are reserved for student poster presentations:
The council of the German Association of Crystal Growth (DGKK) awards a prize for the best poster of master and PhD students, who attend the school and present a poster at the conference. The prize will be 250,00 Euro
The council of the Italian Association oc Crystallography (AIC) awards a prize for the best poster of master and PhD students. The prize will be 250,00 Euro
Elsevier awards 3 poster prizes one for each section of the Handbook of Crystal Growth(2nd edition): Fundamentals, Bulk Crystal Growth and Thin Film and Epitaxy. The prizes are the corresponding volumes of the category.
Poster prizes will be announced during the social dinner.
PLENARY LECTURES
WEDNESDAY 9 September 2015 09:15-10:00 "The Joys and Challenges of Macromolecular Crystallization" Professor NAOMI CHAYEN Professor of Biomedical Sciences Faculty of Medicine, Department of Surgery & Cancer, Imperial College, London
THURSDAY 10 September 2015 09:00-09:45 "Blue light emitting diodes: when growth and physics go together" Professor NICOLAS GRANDJEAN PhD - ICMP Director Institute of Condensed Matter Physics (ICMP) Ecole polytechnique fédérale de Lausanne (EPFL)
MEETING TIMETABLE
PROGRAM
TUESDAY 8 September 2015
Auditorium Enzo Biagi – Sala Borsa 17:00 Registration Open
18:30 Welcome Cocktail
WEDNESDAY 9 September 2015
Main Lecture Theatre – Room 105 09:00-09:15 Opening
Giuseppe Falini, Department of Chemistry «Giacomo Ciamician», University of Bologna Andrea Zappettini, Institute of Materials for Electronics and Magnetism, CNR, Parma Main Lecture Theatre – Room 105 09:15-10:00 Plenary lecture I Chair: Simona Fermani
"The Joys and Challenges of Macromolecular Crystallization" Naomi Chayen, Faculty of Medicine, Department of Surgery & Cancer, Imperial College, London Main Lecture Theatre – Room 105 Room 215 10:00-11:05 SESSION 1a: Fundamentals of Nucleation and SESSION 9a: Fundamentals - Structural Growth Kinetics Defects and their characterization in Chair: Hans Erik Lundager Madsen Crystalline Materials Chairs: Thierry Duffar & Bogdan Ranguelov
10:00-10:20 “Numerical Modelling of Liquid Phase Diffusion "Cellular dislocation patterns in “Mono-like” growth of SiGe with uniform compositions” silicon grown by seeded directional solidification Keynote: Dost Sadik, M. Sakhon, N. Armour of the melt " Keynote: Vanessa Amaral de Oliveira, Marina Rocha, Thu-Nhi-Tran-Thi, Maria Tsoutsouva, José Baruchel, Denis Camel
10:20-10:35 “An in situ view of nucleation” “Nonstoichiometry problems of AIIBVI vapor De Yoreo, James J., Ma, Xiang, Nielsen, Michael grown crystals" H., Chen, Chun-Long Avetissov Igor, Andrew Khomyakov, Albert Davydov, Elena Mozhevitina, Vladimir Chegnov, Nikolai Zhavoronkov
10:35-10:50 “Homogeneous nucleation in small droplets near "Influence of growth conditions on the optical, critical supercooling” mechanical and electrophysical properties the Zdeněk Kožíšek, Pavel Demo lanthanum-gallium silicate group crystals" Buzanov Oleg, Kozlova Nina, Kozlova Anna, Zabelina Evgeniya, Siminel Nikita, Spassky Dmitriy
10:50-11:05 “Separation of nucleation and growth stages - a "Micro-structural characterization of directionally way for studying crystal nucleation kinetics and to solidified eutectic oxides" rule a crystallization process designed to reduce Cherif Maya, Gourav Sen, Vicky Vikram Das, crystal polydispersity” Laurent Carroz, Omar Benamara, Michel Nanev Christo Nanev, Tonchev Vesselin D. Parlier, Thierry Duffar 11:05-11:25 Coffee break Main Lecture Theatre – Room 105 Room 215 11:25-12:45 SESSION 1b: Fundamentals of Nucleation and SESSION 9b: Fundamentals - Structural Growth Kinetics Defects and their characterization in Chair: Hans Erik Lundager Madsen Crystalline Materials Chairs: Thierry Duffar & Bogdan Ranguelov
11:25-11:45 “Beams and Blocky Crystals: Another Challenge "Towards bulk cubic silicon carbide: Growth from the Naica Giant Crystals” mechanisms and related defects" Keynote: Otálora Fermin, Joaquín Criado, Juan- Keynote: Yakimova Rositsa Manuel Garcia-Ruiz
11:45-12:00 “Origin of energy efficiency of axial vibration "Second-phase particle migration via control technique in melt growth process” Temperature Gradient Zone Melting" Zharikov Evgeny, Andrey Sadovskiy, Ekaterina Kerry Wang, Andrew Yeckel, Jeffrey J. Derby Sukhanova, Vladimir Kostikov, Igor Avetissov
12:00-12:15 “Growth of branched rutile-type TiO2 via self- "Effects of Annealing Treatments on assembly and crystal twinning” Microstructures of Aluminum Nitride Buffer Jordan Vanja, Rečnik Aleksander Layer Grown by MOVPE" Kuwano Noriyuki, Kaur Jesbains, Fukuda Junya, Soejima Yohei, Mitsuhara Masatoshi, Suzuki Shuhei, Miyake Hideto, Hiramatsu Kazumasa, Fukuyama Hiroyuki
12:15-12:30 “Selective crystallisation of the more stable ß "The role of screw dislocations in habit polymorph of L-glutamic acid in an acoustic modification of KDP by impurity" levitator” Lai Xiaojun, Kevin Roberts, Helmut Klapper Rusin Michal, Ristic Radoljub Ivan, Gnutzmann Tanja, Emmerling Franziska
12:30-12:45 “Enhanced Crystallization Efficiency of an Active "The role of twin boundaries in growth of natural Pharmaceutical Ingredient through the Formation and Fe-doped SnO2 crystals" of Micron-Sized Crystals in the Undersaturated Tominc Sara, Nina Daneu, Aleksander Rečnik State” Rimez Bart, Edith Norrant, Benoît Haut, Benoit Scheid 12:45-13:45 Lunch
13:45-15:45 Poster Session A: from Session 1 to Session 5
15:45-16:00 Coffee break Main Lecture Theatre – Room 105 Room 215 16:00-18:10 SESSION 4a: Bulk Crystal Growth SESSION 10: Nanostructures & Nanoporous Chairs: Janis Virbulis & Ewa Talik Crystals Chair: Florinda Costa
16:00-16:20 “A new large-lattice-constant perovskite substrate "Nucleation approach to polytypism in III-V crystal” nanowires" Keynote: Uecker, Reinhard, Klimm, Detlef, Keynote: Jonas Johanson, Zeila Zanolli, Bertram, Rainer, Guguschev, Christo, Brützam, Kimberly A. Dick Mario, Kwasniewski, Albert, Klupsch, Michael, Gesing, Th.M., Schlom, D.G.
16:20-16:40 “Floating-zone Growth of Large Single-Crystal of "InAs/GaAs sharply-defined axial Haldane Chain Compound SrNi2V2O8” heterostructures in self-assisted nanowires" Keynote: A.T.M. Nazmul Islam, B. Lake, A.K. D. Scarpellini, C. Somaschini, A. Fedorov, Bera, B. Klemke, E. Faulhaber, J.M. Law, A. Sergio Bietti, C. Frigeri, V. Grillo, L. Esposito, Schneidewind, J.T. Park, E. Wheeler M. Salvalaglio, A. Marzegalli, F. Montalenti, E. Bonera, P. G. Medaglia, S. Sanguinetti
16:40-16:55 “Europium and potassium co-doped strontium "Mass-transport driven growth dynamics of metaborate single crystals grown by the AlGaAs shells deposited by metalorganic vapor Czochralski method” phase epitaxy around dense GaAs nanowire Głowacki Michal, Solarz Piotr, Ryba- ensembles" Romanowski Witold, Martín Inocencio R., Ilio Miccoli, Paola Prete, Nico Lovergine Diduszko Ryszard, Berkowski Marek
16:55-17:10 “Flux growth and characterization of highly Yb3+- "Low Temperayure Growth of Porous ZnO substituted cubic RE2O3 (RE=Gd, Y, Lu) laser Films for Inorganic–Organic Hybrid Solar Cells" crystals and of cubic Lu1.56Gd0.41Eu0.03O3 crystals” Yoshino Kenji, Akiko Mochihara, Himeka Matias Velázquez, Philippe Veber, Gabriel Buşe, Tominaga, Youei yamaga, Takashi Minemoto, Yannick Petit, Philippe Goldner, Olivier Plantevin, Shigeru Ikeda Daniel Rytz, Emmanuel Véron, Rekia Belhoucif, Véronique Jubera, Patrick Aschehough, Gérard Aka
17:10-17:25 “On the crystal growth of incongruent borate type "Growth of ZnO nanostructures through rapid crystal LaxGdyScz(BO3)4 (x + y + z = 4) by the crystallization" Czochralski method” Fioravanti Ambra, Bonanno Antonino, Carotta Lucian Gheorghe, Flavius Voicu, Gabriela Maria Cristina, Sacerdoti Michele Salamu, Federico Khaled, Alexandru Achim, Cristina Gheorghe, Pascal Loiseau, Nicolaie Pavel, Gérard Aka
17:25-17:40 “Improvement of crystal growth of Li4SiO4 single "Heat of Fusion of Nano Crystals" crystals for neutron detection and their scintillation Clain Alexander E., Novins Caleb A., Amanuel and luminescence properties” Samuel Jan Pejchal, Vladimir Babin, Alena Beitlerova, Shunsuke Kurosawa, Yuui Yokota, Akira Yoshikawa, Martin Nikl
17:40-17:55 “Synthesis and characterization of Ba2Cu1- "Filamentary growth of metals" xNixGe2O7, x =0, 0.1 single crystals grown by Richter Gunther floating zone technique” Fittipaldi Rosalba, Rocco Luisa, Ciomaga Hatnean Monica, Granata Veronica, Lees Martin, Balakrishnan Geetha, Vecchione Antonio
17:55-18:10 “Crystallization of Al2O3-YAG-ZrO2 eutectic “A comparative numerical analysis of circular ceramic plates by the EFG technique” and rectangular well nanopatterning on c-plane Laurent Carroz, Maya Cherif, Nicolas Barthaley, sapphire substrates for selective area growth of
José Peirrera, Thierry Duffar AlN islands” M. Chitra, I. Davis Jacob Room 215 18:10-19:10 Meeting Delegates ENCG
THURSDAY 10 September 2015
Main Lecture Theatre – Room 105 09:00-09:45 Plenary lecture II Chair: Roberto Fornari
"Blue light emitting diodes: when growth and physics go together" Nicolas Grandjean, ICMP, Ecole polytechnique fédérale de Lausanne Main Lecture Theatre – Room 105 Room215 09:45-10:50 SESSION 4b: Bulk Crystal Growth SESSION 5a: Advance in Crystal Growth Chairs: Janis Virbulis & Ewa Talik Technology Chairs: Evgeny Zharikov & Christiane Frank- Rotsch
09:45-10:05 “New results in adsorption at semiconductor “Numerical modeling and experimental surfaces - consequences to growth and doping of validation of electromagnetical stirring in semiconductor from the vapor” unidirectional solidification of multicrystalline Keynote: Krukowski Stanisław, Pawel Kempisty, silicon” Pawel Strąk, Maria Ptasinska, Jacek Piechota Keynote: Negrila Radu Andrei, Popescu Alexandra, Vizman Daniel
ù10:05-10:20 “Range of the temperature gradients and the “Crystal Growth of Cd1-xZnxTe by the Traveling growth rate values in the growth of CZT crystals Heater Method in Microgravity on Board of from the melt” Foton-M4 Spacecraft” Repiso Eva, Corrochano Álvaro, Rubio Sandra, Borisenko Elena B., N. N. Kolesnikov, A. S. Plaza Jose Luis, Tsybrii Zinoviia, Vuichyk Mykola, Senchenkov, M. Fiederle Dieguez Ernesto
10:20-10:35 “Growth and Performance of Large ZnGeP2 “Modified Bridgman technique for growing Sb- Single Crystals” based binary compounds” Chunhui Yang, Zuotao Lei, Chongqiang Zhu, Pillaca Quispe Mirtha, Miller Wolfram, Liangcheng Song Cocivera Viviane, Maletin Tamara, Gille Peter
10:35:10:50 “Crystal growth, physical properties and Appendix to SESSION 10: applications of mixed and complex halides” "Dual-Type Compound Semiconductor Edith Bourret, Zewu Yan, Eric Samulon, Tetiana Nanowire Arrays" Shalapska and Didier Perrodin Joona-Pekko Kakko, Farid Bayramov, Bakhysh Bairamov, Tuomas Haggrén, Veer Dhaka, Teppo Huhtio, Antti Peltonen, Hua Jiang, Esko Kauppinen, Harri Lipsanen 10:50-11:10 Coffee break Main Lecture Theatre – Room 105 Room 215 11:10-12:30 SESSION 4c: Bulk Crystal Growth SESSION 5b: Advance in Crystal Growth Chairs: Janis Virbulis & Ewa Talik Technology Chairs: Evgeny Zharikov & Christiane Frank- Rotsch
11:10-11:30 “Modeling of dopant transport in gas and melt “Experimental evidence that a high electric field during silicon FZ crystal growth” acts as an efficient external parameter during Keynote: Sabanskis Andrejs, Surovovs Kirils, crystalline growth of bulk oxide” Virbulis Jānis Keynote: Haumont Raphaël, P. Hicher, R. Saint-Martin, X. Mininger, P. Berthet
11:30-11:45 “Impact of growth rate fluctuations on the bulk “High-pressure and ambient gas effect on the quality of Czochralski silicon crystals” optical floating zone crystal growth of novel Gaspar Guilherme, Lanterne Adeline, Jensen oxide and intermetallic compounds” Øyvind, Lehmann Toni, Hagen Vegard, Kildemo Sass Paul, Robert Schöndube Morten, Di Sabatino Marisa, Arnberg Lars, Øvrelid Eivind
11:45-12:00 “Reduction of carbon contamination during the “Growth of Shaped Oxide Eutectics by the EFG melting process of Czochralski silicon crystal Technique” growth” Stryukov Dmitry, Shikunova Irina, Kurlov Xin Liu, Bing Gao, Satoshi Nakano and Koichi Vladimir Kakimoto
12:00-12:15 “N-type doping of bulk gallium nitride grown by “High-pressure crystallization of organic hydride vapour phase epitaxy” compounds in a diamond-anvil cell” Patrick Hofmann, Frank Habel, Martin Krupinski, Andrzejewski Michal, Andrzej Katrusiak Gunnar Leibiger, Franziska Christine Beyer, Stefan Eichler, Thomas Mikolajick
12:15-12:30 “Growth of 5 kg-level LBO for ultrashort and “Direct measurement of the crystallization ultrahigh power laser” pressure at the pore scale” Zhanggui Hu, Yinchao Yue, Ying Zhao, Heng Tu Desarnaud Julie, Daniel Bonn, Noushine Shahidzadeh 12:30-13:30 Lunch
13:30-15:30 Poster Session B: from Session 6 to Session 11
15:30-15:50 Coffee break Main Lecture Theatre – Room 105 Room 215 15:50-18:00 SESSION 2a: Theory and Modeling SESSION 8a: Epitaxial Growth - Crystal Growth Chair: Liliana Braescu Interfaces Chairs: Josef Novak & Luca Seravalli
15:50-16:10 “Collaboration of atomic and macro scale "Analysis of critical thickness for generated calculations: polytype and defect control of wide misfit dislocation in GaInN/GaN superlattice on bandgap material” GaN by in situ X-ray diffraction" Keynote: Koichi Kakimoto, Bing Gao, Shin-ichi Keynote: Ohsumi Junya, Koji Ishihara, Taiji Nishizawa, Satoshi Nakano, Yoshihiro Kangawa Yamamoto, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki
16:10-16:30 “Gaining understanding of crystal growth “In situ observation of low temperature growth processes via modeling: Pushing the continuum of Ge on Si(111) via RHEED” from the top down” Keynote: Grimm Andreas, Andreas Fissel, Keynote: Yutao Tao, Andrew Yeckel, Jeffrey J. Eberhard Bugiel, H. Jörg Osten, Tobias F. Derby Wietler
16:30-16:45 “Study on the usage of a commercial software “Structural and electrical characteristics of (Comsol multiphysics®) for dislocation AlGaN/GaN heterostuctures with thin AlN multiplication model” interlayer on sapphire substrate grown by B. Gallien, M. Albaric, J.P. Garandet, Thierry MOCVD" Duffar, K. Kakimoto, M. M’Hamdi Raju Ramesh, Kandasamy Prabakaran, Ravi Loganathan, Manavaimaran Balaji, Eric Faulques, Alexandre Crisci, Krishnan Baskar
16:45-17:00 “Atomic scale design of epitaxial interfaces: "Two-dimensional Si/Si(111)-(7×7) nucleation clusters, stripes and nanowires” affected by step permeability and sink to atomic Michail Michailov, Bogdan Ranguelov steps" Rogilo Dmitry, Fedina Liudmila, Kosolobov Sergey, Ranguelov Bogdan, Latyshev Alexander
17:00-17:15 “Numerical analysis of dislocation density in "Epitaxial growth of Ge/Si nanostructures on Si multicrystalline silicon for solar cells using surface patterned by ion irradiation" experimental verification” Smagina Zhanna Victorovna, A.V. Zinovyev, Satoshi Nakano, Bing Gao, Karolin Jiptner, N.P. Stepina, A.F. Zinovieva, S.A. Rudin, P.L. Hirofumi Harada, Yoshiji Miyamura, Takashi Novikov, V.A. Seleznev, A.V. Dvurechenskii Sekiguchi, Masayuki Fukuzawa, Koichi Kakimoto
17:15-17:30 “Numerical Modeling of Titanium Distribution in "Self-assembled strained GeSi nanoscale Sapphire Crystals Grown by the Kyropoulos structures grown by MBE on Si(100)" Method” Nikiforov Alexandr, Vyacheslav Timofeev, Carmen Stelian, Gourav Sen, Nicolas Barthalay, Artur Tuktamyshev, Michail Esin, Serge Teys, Thierry Duffar Oleg Pchelyakov
17:30-18:45 “Evolution of grains during solidification of silicon "Quantum dot chains in InAs/GaAs multistacked – attempts of numerical simulations for an structures grown by MBE: a strain analysis by understanding” FEM" Miller Wolfram, Popescu Alexandra Latini Valerio, Placidi Ernesto, Arciprete Fabrizio, Magri Rita, Patella Fulvia
17:45-18:00 “Analytic scaling function for size distributions of “A study of β-Ga2O3 hetero-epitaxial layers 2D surface islands” grown by MOCVD and ALD”" Vladimir G. Dubrovskii, N. V. Sibirev, Yu. S. F. Boschi, M. Bosi, E. Buffagni, T. Berzina, C. Berdnikov Ferrari, Fornari Roberto 20:00 Social Dinner
FRIDAY 11 September 2015
Main Lecture Theatre – Room 105 Room 215 09:00-11:10 SESSION 11: Novel Materials and Structures SESSION 3: Product and Process Design of Chairs: Peter Gille & Harri Lipsanen Pharmaceuticals and Fine Chemicals Chair: Kevin Roberts
09:00-09:20 “In-situ observations of the catalytic growth of “Using crystal growth to generate single nanomaterials” chirality from an achiral start” Keynote: Hofmann Stephan Keynote: Rene Steendam, Jorge Verkade, Tim van Benthem, Hugo Meekes, Willem van Enckevort, Jan Raap, Floris Rutjes, Elias Vlieg
09:20-09:35 “Crystal engineering of molecular solids: “light“ “Crystallisation Characteristics of an Organic
interactions for interactions with light” Material in Industrial Mother Liquor with Grepioni Fabrizia, Simone d'Agostino, Dario Impurities” Braga, Barbara Ventura, Mirko Seri Keynote: Khan Shahid, Mahmud Tariq, Roberts Kevin, Zhu Xiaofeng, George Neil, Sillers Pauline
09:35-09:50 “Chemical Vapor Transport towards new geo- “Preferential Orientation of β-phase inspired selenite-based materials” Triacylglycerol on Graphite Surface” Colmont Marie, Minfeng Lü, Almaz Aliev, Jacob Fumitoshi Kaneko, Shinichi Yoshikawa, Olchowka, Marielle Huvé, Olivier Mentré Haruyasu Kida, Kiyotaka Sato
09:50-10:05 “Spectroscopic examinations of Lu3Al5O12:Pr “Crystallization of L-Glutamic acid polymorphs single crystals” in stirred and stagnant conditions” Guzik Adam, Talik Ewa, Pajączkowska Anna, Tahri Yousra, Gagnière Emilie, Chabanon Szubka Magdalena, Kusz Joachim, Balin Elodie, Bounahmidi Tijani, Mangin Denis Katarzyna, Urbanowicz Piotr
10:05-10:25 “Crystal growth from high-pressure melt and “Design of Optimal Start-up Procedures for Chemical Vapor Transport of (Si,Ge) MSMPR Crystallizers” monopnictides, a new family of 2D- Kamaraju Vamsi Krishna, Power Graha, Hou semiconductors” Guangyang, Zhao Yan, Glennon Brian Keynote: Barreteau Céline, Baptiste Michon, Enrico Giannini
10:25-10:40 “Superconductivity in single crystals of alkali metal “A phenytoin polymorph accessible via surface intercalated iron chalcogenides” mediation” A. Krzton-Maziopa, E. Pomjakushina, Conder Daniela Reischl, Christian Röthel, Eva Roblegg, Kazimierz Heike M.A. Ehmann, Oliver Werzer
10:40-10:55 “Crystal growth of rare earth containing clathrates “Nucleation Kinects of Co-crystal by and mechanism of rare earth incorporation into the Simultaneous Monitoring of Dissolution and clathrate cages” Crystallisation using Process Raman Prokofiev Andrey, Robert Svagera, Monika Technique: Precipitation of Burkeite” Waas, Johannes Bernardi, Silke Paschen Boyang Zou, Xiaojun Lai, Dan Xu, Luis Martin de Juan
10:55-11:10 “Flux growth at 1230°C of cubic Tb2O3 single "Continuous production of lactose monohydrate crystals and characterization of their optical and crystal seed suspensions by rapid antisolvent magnetic properties” crystallization using a continuous nucleation Velázquez Matias, Philippe Veber, Grégory unit” Gadret, Olivier Plantevin, Daniel Rytz, Mark Peltz, Pól MacFhionnghaile, John McGinty, Jan Rodolphe Decourt Sefcik 11:10-11:30 Coffee break Main Lecture Theatre – Room 105 Room 215 11:30-13:40 SESSION 7: In-situ Monitoring ⁄ Control of Crystal SESSION 6: Mesocrystals and Nonclassical Crystallisation ⁄ Growth of Biological Growth Processes ⁄ Crystal morphology Materials and Biologically-Controlled Growth Chairs: Alexander van Driessche & Carlos M. Pina Chairs: Damir Kralj & Jaime Gómez Morales
11:30-11:50 “Mechanistic insights into the early stages of "Multiscale Approach of the Bio Crystal Status crystallization of rare-earth carbonates" and Growth in Mollusc Shells" Keynote: Rodriguez-Blanco Juan Diego, Keynote: Baronnet Alain Dideriksen, Knud, Tobler, Dominique J., Sand, Karina K., Vallina, Beatriz, Benning, Liane G., Stipp, Susan
11:50-12:10 "From Amino Acids to Cements: Crystallization "Bio-inspired Composite Crystals. Incorporation Studied by CLASSIC NMR" of nanoparticles in calcite and zinc oxide single Keynote: Hughes Colan, Williams, P. Andrew; crystal" Keast, Victoria L.; Edwards-Gau, Gregory R.; Keynote: Kulak Alexander, Pengcheng Yang, Charalampopoulos, Vasileios G.; Harris, Kenneth Mona Semsarilar, Oscar Cespedes, Yi-Yeoun D. M.; Gardner, Laura J.; Walling, Sam A.; Bernal, Kim, Steven P. Armes, Fiona C. Meldrum Susan A.; Provis, John L.
12:10-12:25 "An Investigation into the Particle Growth Pathway "Optimization of Crystallization using Dialysis of Precipitated Fenofibrate" Combined with Temperature Control" Tierney Teresa, Rasmuson, Åke C., Hudson, Niels Junius, Esko Oksanen, Maxime Terrien, Sarah P. Christophe Berzin, Jean-Luc Ferrer, Budayova - Spano Monika
12:25-12:40 "Growth of nanostructured carbon materials by "Influence of shear rate and surface area on Supersonic Molecular Beams of C60 on Cu nucleation kinetics in aqueous solutions of studied by Surface Electron Spectroscopies" glycine and urea reveals nonclassical Aversa Lucrezia, Tatti Roberta, Taioli Simone, nucleation mechanisms" Garberoglio Giovanni, Speranza Giorgio, Carol Forsyth, Danielle Trap, Sefcik Jan Cavaliere Emanuele, Gavioli Luca, Iannotta Salvatore, Verucchi Roberto
12:40-12:55 "Grain growth competition in directionally solidified "Infrared light-induced protein crystallization" multi-crystalline silicon studied with in situ X-ray Kowacz Magdalena, Marchel Mateusz, imaging techniques" Juknaitė Lina, Esperança José M. S. S., Romão Thècle Riberi-Béridot, Nathalie Mangelinck-Noël, Maria João., Carvalho Ana Luísa., Rebelo Luís Amina Tandjaoui, Guillaume Reinhart, Maria Paulo N.* Tsoutsouva, Gabrielle Regula, José Baruchel
12:55-13:10 "Evaporation Crystallization of Glycine" "Precursor-based bioinspired synthesis of Puranen Johanna, M. Louhi-Kultanen magnetite nanocrystals" Mirabello Giulia, Söğütoğlu Leyla-Can, Lendesr Jos J.M., Sommerdijk Nico A.J.M
13:10-13:25 "Polymer versus monomer action on the growth "Co-processing of Metformin Hydrochloride with and habit modification of sodium chloride crystals" Hydroxypropyl Methylcellulose and Sodium Townsend Ellie, W.J.P. van Enckevort, J.A.M. Carboxymethlycellulose during Crystallization to Meije, E. Vlieg Manufacture Extended Release Tablets" Erdemir Lee Deniz, Chang Shih-Ying, Wong Benjamin, Rosenbaum Tamar, Kientzler Donald, Wang Steve, Desai Divyakant, Kiang San
13:25-13:40 "Application of LPE method for producing of high- "Heterogeneous nucleation and growth of performance scintillating screens based on the calcium phosphate films on mica sheets by single crystalline films of multicomponent garnets" vapour diffusion" Yu. Zorenko, T. Zorenko, V. Gorbenko, T. Gómez Morales Jaime Voznyak, O. Sidletskiy, Ya. Gerasymov, A. Fedorov 13:40-14:30 Lunch Main Lecture Theatre – Room 105 Room 215 14:30-16:25 SESSION 2b: Theory and Modeling SESSION 8b: : Epitaxial Growth - Crystal Chair: Liliana Braescu Growth Interfaces Chairs: Josef Novak & Luca Seravalli
14:30-14:50 “On Modeling Interface Attachment Kinetics in “Step density waves on vicinal crystal surfaces" Melt and Solution Growth Systems” Keynote: Keynote: Oleg Weinstein, Oren Bass, Alexander Ranguelov Bogdan Stavrev, Stoyan Stoyanov Virozub, Andrew Yeckel, Wolfram Miller, Jeffrey J. Derby, Simon Brandon
14:50-15:10 “Tailoring crystal growth more and more “Structural study of the innovative 3C-SiC/Si/3C quantitatively via multiscale simulations” SiC/Si heterostructure for electro-mechanical Keynote: Heike Emmerich applications" Keynote: Khazaka Rami, J.F. Michaud, P. Vennéguès, D. Alquier, M. Portail
15:10-15:25 “Phase field simulations of particle capture during "Functionalization of SiC Nanowires by directional solidification of silicon for solar cells” Supersonic Molecular Beams for Photodynamic Heike Emmerich, Hörstermann Henning, Kundin Therapy" Julia, Friedrich Jochen, Azizi Maral, Reimann Tatti Roberta, Aversa Lucrezia, Verucchi Christian, Cröll Arne, Jauß Thomas, Sorgenfrei Roberto, Fabbri Filippo, Rossi Francesca, Tina Attolini Giovanni, Bosi Matteo, Salviati Giancarlo, Iannotta Salvatore
15:25-15:40 “Phase-field study of morphological evolution "Characterisation of sub-micrometer yttrium iron during directional solidification: influence of garnet LPE films with low ferromagnetic temperature gradient and convection” resonance losses" Ankit Kumar, Selzer, Michael, Bhattacharya, Dubs Carsten, Surzhenko Oleksii, Linke Ralf, Avisor, Nestler, Britta Jauß Thomas, Danilewsky Andreas
15:40-15:55 “Phase Field Crystal Modeling of Heterogeneous "Liquid phase epitaxial growth of GdAP and Nucleation and Heteroepitaxy” GdLuAP scintillating films for synchrotron László Gránásy, Frigyes Podmaniczky, Gyula I. imaging" Tóth, György Tegze, Tamás Pusztai Riva Federica, Douissard Paul-Antoine, Martin Thierry, Zorenko Yuriy, Petrosyan Ashot, Dujardin Christophe
15:55-16:10 “Phase-field Modelling of Spiraling Ternary "Controlling Polymorphism in Organic Thin Eutectic Dendrites” Films by Light" László Rátkai, Tamás Pusztai, Attila Szállás, Pithan Linus, Caterina Cocchi, Christopher László Gránásy Weber, Anton Zykov, Sebastian Bommel, Steven J. Leake, Peter Schäfer, Claudia Draxl, Stefan Kowarik
16:10-16:25 “Time Evolution of 2D Cellular Automata with "PDIF-CN2 organic thin-film deposited at room “Crystal Growth” Rules” temperature by supersonic molecular beam Alexander Kolevski, Hristina Popova, Georgi As. deposition for n-type OTFT" Georgiev, Vesselin Tonchev Chiarella Fabio, Barra Mario, Chianese Federico, Toccoli Tullio, Cassinese Antonio Main Lecture Theatre – Room 105 16:25 Final greetings
POSTER PRESENTATIONS
1 - Fundamentals of Nucleation and Growth Kinetics S01-P02 - Experimental research of phase transitions in a liquid melt of high-purity aluminum Borisovith, Vorontsov Vadim S01-P03 - On the Theory of Ostwald Ripening: Formation of the Universal Distribution Function in the Presence of Different Mass Transfer Mechanisms Alexandrov, Dmitri V S01-P04 - Influence of shear rate on nucleation in oscillation baffled crystallizer. Yang, Huaiyu S01-P05 - Interferometric Observation of Concentration Field during the Growth of Tetrahydrofuran Clathrate Hydrate in the Guest/Host Boundary Layer. Nagashima, Kazushige
S01-P06 - Study of crystallization processes in Bi-doped As2S3 chalcogenide glasses using linear isoconversion methods. Lukic-Petrovic, Svetlana S01-P08 - Influence of ionic surfactants on sodium chloride crystallization during evaporation. Qazi, Mohsin Jahan S01-P09 - A Study of Crystal Growth of Salicylic Acid in Organic Solvents. Jia, Lijun S01-P10 - "Influence of sintering aid (SiO2) on optical properties of ceramic YAG:Cr,C". Chaika Mihail S01-P11 - Laser-Induced Nucleation in Continuous Flow. Mackenzie, Alasdair Morgan
S01-P13 - Understanding of Crystallization and Growth of LiB3O5 crystal in the MoO3-based high-temperature solution at the Molecular Level. Wang, Di
S01-P14 - Growth of doped KDP single crystals from solutions with KMnO4 additives. Egorova, Anna S01-P15 - Study on Growth Kinetics of Partially Deuterated Potassium Dihygrogen Phosphate (p-DKDP) Crystals for High Power OPCPA. Guzman, Luis A. S01-P16 - Thinning and thickening of free-standing smectic films. Pikina, Elena S01-P17 - In-situ SAXS studies of crystal structures of C16/C18 binary system during crystallisation and phase transformations in melts. Tang, Xue S01-P18 - Solution state studies of C16H24/C18H38 binary system in dodecane from poly-thermal crystallisation process. Tang, Xue S01-P19 - Nucleation of Amine Soaps. Booth, David S01-P20 - Nucleation, crystal growth kinetics and morphology of methyl stearate as a function of solution environment. Camacho Corzo, Diana Milena S01-P21 - Metastability limit for the nucleation of NaCl crystals in confinement. Shahidzadeh, Noushine S01-P22 - The role of alanine, aspartic acid and lysine as simple models of organic matrix molecules participating in calcium carbonate biomineralization. Stajner, Lara S01-P23 - Crystallization kinetics of iron inclusion in magnesium aluminosilicate glass processed by laser floating zone technique.
Ferreira, Nuno M. S01-P24 - The NMR study of 3He enclosed in nanotubes MCM-41. Fysun, Yana S01-P25 - Block copolymer aggregates on planar substrates: Impact of preparation conditions and surface wettability. Danglad Flores, José Angel S01-P26 - Switching off Non photochemical laser induced nucleation by use of nanofiltration. Kendall, Thomas Gilbert
2 - Theory and Modeling S02-P01 - Atomic scale design of epitaxial interfaces: clusters, stripes and nanowires. Michailov, Michail S02-P02 - A single-domain approach to simulate the effect of convective flow on the mushy zone structure in Czochralski growth of semitransparent oxide crystal. Faiez, Reza S02-P03 - Modeling of patterns by the phase field crystal method in three dimensions. Starodumov, Ilya S02-P04 - Kinetic Monte Carlo simulations of vicinal GaN(000-1) surface evolution during N-rich growth. Krzyzewski, Filip S02-P05 - Modeling of dendritic growth under earthly and reduced gravity conditions. Galenko, Peter S02-P06 - Relationship between stability of facet surfaces and incorporation of zinc-blende phase in InN during pressurized reactor MOVPE: A theoretical approach. Kusaba, Akira S02-P07 - Study of the early stages of Calcium Phosphate nucleation in water by means of ab Initio Molecular Dynamics. Mancardi, Giulia S02-P08 - On obtaining equilibrium crystal shape under non stationary conditions. Skorynina, Alina A. S02-P09 - Working point of the EFG process. Carroz, Laurent S02-P11 - Kinetic model of cement hydration with time-dependent rates. Valentini, Luca S02-P12 - Crystal surface morphology as a consequence surface diffusion anisotropy. Zaluska-Kotur, Magdalena Anna S02-P13 - Monte Carlo simulation of island formation during GaAs(001) homoepitaxial growth. Balakirev, Sergey Vyacheslavovich S02-P14 - Mathematical modeling of the process of growing a single crystal CdTe 100 mm by the Obreimov-Shubnikov method. Pavlyuk, Marina S02-P16 - Experimentally Verified Numerical Simulation of Germanium Single Crystals Grown by the AVC-AHP Technique. Yousefi, Pouya S02-P17 - Microscopic modelling of confined crystal growth and dissolution. Høgberget, Jørgen S02-P18 - Dendritic Growth Kinetics in Undercooled Melts under Static Magnetic Fields. Gao, Jianrong S02-P19 - Multiphase-field theories of crystallization: A comparative study. Toth, Gyula S02-P21 - Thermoelectric Control of Crystal Growth. Pericleous, Koulis S02-P22 - Orientation-field model for polycrystalline solidification in binary alloys with a singular coupling between order and orientation.
Korbuly, Bálint S02-P23 - Rotationally-driven, axisymmetric oscillatory convection in a semitransparent Czochralski melt model. Faiez, Reza S02-P24 - Thermal stability and spontaneous breakdown of free-standing metal nanowires. Giazitzidis, Paraskevas S02-P25 - Towards the understanding of hydrozincite precipitation; Population balances on sparingly soluble compounds. Martín-Soladana, Pablo Miguel S02-P26 - Effects of boundary conditions and geometry on structural and thermodynamic properties of modeled semiconductors. Podolska, Natalia S02-P27 - The Conductivity Of Two-Dimensional Electron Crystal On The Surface of liquid 4He. Modeling. Sharapova, Iryna S02-P28 - Transitions between regimes of crystal growth kinetics under decaying supersaturation. Tonchev, Vesselin Dimitrov S02-P29 - Effect of surface reconstruction on Ge-Si(001) heteroepitaxy. Ghosh, Paramita S02-P30 - Interatomic distances and thermodynamic properties of wurtzite and zinc blende AlInGaN. Podolska, Natalia S02-P31 - A numerical model on nano-line patterning of c-plane sapphire substrates for selective area growth of AlN islands. Jacob, Davis S02-P32 - Modeling of axial heterostructure formation in multicomponent III-V nanowires. Koriakin, Aleksandr
3 - Product and Process Design of Pharmaceuticals and Fine Chemicals S03-P03 - Achiral molecules in engineering of non-centrosymmetric crystal structures: polymorphs and co-crystals of 1H-3,5- dinitropyridine-2-one. Fedyanin, Ivan S03-P05 - Non-Photochemical LASER-Induced Nucleation in Water/Ethanol of sulfathiazole. Li, Wenjing S03-P06 - Purification of fermentatively produced specialty carbohydrates. Bekers, Katelijne S03-P12 - Crystallisation Characteristics of an Organic Material in Industrial Mother Liquor with Impurities. Mahmud, Tariq
4 - Bulk Crystal Growth
S04-P01 - Bulk growth of optical quality inverted Solubility Li2SO4.H2O single crystals by the improved Sankaranarayanan - Ramasamy method. Silambarasan, A
S04-P04 - TSFZ-growth, magnetism and ac conductivity of LiMn(1-x)Fe(x)PO4 single crystals. Neef, Christoph
S04-P06 - Czochralski growth of bulk Li2MoO4 crystals for the scintillating bolometers used in the rare events searches. Velazquez, Matias S04-P07 - Czochralski growth and physical properties characterizations of 6Li- and 10B-enriched crystals for heat-scintillation cryogenic bolometers used in the rare events searches. Velazquez, Matias S04-P09 - Influence of melt convection on the aggregation of inclusion in massive sapphire and garnet crystals for growing by HDC method. Tanko, Alina S04-P10 - New insights on growth rate limitations of the Traveling Heater Method. Derby, Jeffrey J.
S04-P11 - Growth and Laser performance of a new IR NLO crystal BaGa4Se7. Yao, Jiyong
S04-P12 - Growth from the melt, structure and properties of the crystals of (ZrO2)1-x(Sc2O3)x solid solutions. Kulebyakin, Alexey S04-P13 - Bulk crystals of L-Histidinium dihydrogen phosphate orthophosphoric acid grown by Sankaranarayanan - Ramasamy method. Ittyachan, Reena S04-P15 - Control of sapphire crystal morphology grown in a Kyropoulos furnace. Sen, Gourav S04-P16 - Influence of Growth Conditions in Interface shape and Stability in Antimony doped Germanium Single Crystals using VB, AHP, and AVC Techniques. Sheikhi, Aidin S04-P19 - VGF growth of GaAs doped with 12C, 16O and 18O for the study of mid-infrared vibrational modes. Frank-Rotsch, Christiane S04-P20 - The search for novel solvents for the single crystal growth of germanate phases by the flux method. Ivanov, Vladimir A. S04-P21 - The reduction of basal plane dislocations by modifying thermal conductivity of the crucible during PVT growth of 4H-SiC single crystals. Miyazaki, Kazuma S04-P22 - Dosimetric properties of luminescence crystals grown by Micro-Pulling Down Method. Marczewska, Barbara S04-P23 - Optical, Structural and Microhardness Properties of KDP Crystals Grown from L-arginine Doped Solutions. Prytula, Igor M. S04-P24 - Growth and point defect characterization of bulk AlN crystals. Dittmar, Andrea
S04-P26 - Crystal growth of hexaferrits Z structure Ba(Sr)3 Co2 Fe24 O41 by floating zone melting. Balbashov, Anatoly S04-P27 - Mathematical modeling of the process of growing a single crystal CdTe 100 mm by the Obreimov-Shubnikov method. Zykova, Marina S04-P28- Features compensate defects in CdTe using a stepwise cooling of the crystal. Pavlyuk, Marina
S04-P30 - Investigations on synthesis, growth and physical properties of AgGaInS2 single crystals for Mid-IR application. N. Karunagaran
S04-P31 - Crystal Growth and Thermoelectric Properties of Sr2Fe2O5 Single Crystals. Hossain, Md Anwar
S04-P33 - Magnetocaloric and Hopkinson effects in slowly and rapidly cooled Gd7Pd3. Oboz, Monika S04-P35 - Influence of growth parameters on electrical proprieties of highly polluted mc-Si grown by the Bridgman technique with various crucible-coating combinations. Negrila, Radu Andrei
S04-P40 - Optical properties of Cd1-xMnxTe:Fe2+ crystals. Kapustnyk, Oleksii
S04-P41 - Growth of Bi2Te3, Cr2Ge2Te6 and CrSi2Te6 crystals for Topological Interests. Chandran, Bagavath S04-P42 - Characterization of G2-sized quasi-mono Si directionally solidified in TMF. Kiessling, Frank M.
S04-P43 - β-Ga2O3 Crystals Grown from Al2O3-Ga2O3 Melt. Nikolaev, Vladimir
S04-P44 - Growth, structural and magnetic characterization of highly ordered Co2FeSi single crystals. Ramasamy, Mohankumar
S04-P45 - Effect of crucible geometry and fixed heat exchangers in the solid-liquid interface for growing CdZnTe bulk crystals using a Vertical Gradient Freeze technique. Dieguez, Ernesto S04-P47 - High purity Germanium Crystal Growth. Aravazhi, Shanmugam S04-P48 - The influence of finite silicon electrical conductivity on melt flow and dopant transport in floating zone crystal growth process. Surovovs, Kirils S04-P49 - 3D simulation of feed rod melting in floating zone silicon single crystal growth. Plate, Matiss
S04-P50 - Crystal growth and characterization of an oxy-fluoride crystal (BaCaBO3 F) doped with Yb3+ ions for self-frequency doubling: a thrilling challenge. Khaled, Federico Nabil S04-P51 - Ge-containing Quartz Single Crystals - New Advanced Piezoelectric Material. Setkova, Tatiana S04-P52 - Dislocation multiplication during Czochralski growth of germanium: Numerical studies and experimental results. Miller, Wolfram S04-P54 - New technological approaches for electroless deposition of metal contacts on CdZnTe single crystals. Bettelli, Manuele S04-P55 - Impurity distribution in characteristic of multicrystalline silicon growth mode. Nepomnyashchikh, Aleksandr Iosifovich
S04-P56 - Growth of TbFe0.5Mn0.5O3 and Tb0.5Sr0.5MnO3 Single Crystals Using Optical Float-Zone Technique. Hariharan, Nhalil
S04-P57 - SrMoO4:Ho3+:Tm3+ crystal as new active material for mid - IR laser. Dunaeva, Elizaveta S04-P59 - Structural properties and spinodal decomposition of bulk ternary semiconductor compounds with oxygen in the anion sublattice. Podolska, Natalia
S04-P60 - Li2MoO4 crystal growth from solution activated by low-frequency vibrations. Sadovskiy, Andrey P S04-P63 - Numerical modeling of a kyropoulos process to grow square silicon ingots for photovoltaic applications using different configurations and different working parameters. Nouri, Ahmed S04-P64 - Effectivity of chemical vapor transport for ZnO single crystal growth based on HCl vapors. Colibaba, Gleb V S04-P66- Temperature dependent optical absorption of strontium titanate. Kok, Dirk Johannes
5 - Advance in Crystal Growth Technology S05-P01 - Isostructural phase transition of 2,4,5-triiodoimidazole at high pressure. Rajewski Kacper Wojciech
S05-P02 - pH specific single crystal growth of N-Hδ+ Clδ- influenced [ZnCl4]- [R]+ hybrid materials of 3D to 2D lattice dimensionality by organic variant: Microscopy, optical Eg and PL properties. Jasrotia, Dinesh S05-P04 - Heptadecane and Gallium Crystallization in Hydrodynamic Czochralski Model. Prostomolotov, Anatoly Ivanovich S05-P06 - Growth of large size YAG:Ce crystals with homogenous distribution of Ce3+ ions by HDC method for WLED application. Nizhankovskyi, Sergii Victorovich S05-P07 - The approach for reconstruction of GaSb:Te space crystal growing. Prostomolotov, Anatoly Ivanovich
S05-P08 - Influence of melt transparency on critical growth rate of sapphire. Baranov, Viacheslav S05-P09 - Growth of high optical quality ZnS single crystals by solid phase recrystallization technique at barothermal treatment. Avetisov, Roman S05-P10 - Sapphire Shaped Crystals for Medicine. Shikunova, Irina S05-P11 - Salt stains from evaporating droplets. Shahidzadeh, Noushine S05-P12 - Crystal growth under high electric field: Analysis of the nucleation process. Hicher, Patrick
6 - Mesocrystals and Nonclassical Crystallisation ⁄ Growth of Biological Materials and Biologically-Controlled Growth S06-P01 - An Approach for Controlling Epitaxial Growth of Protein Crystal by Using Microfluidic Device. Maeki, Masatoshi S06-P02 - Biogenic and non-biogenic struvite. Prywer, Jolanta S06-P03 - Influence of tetrasodium pyrophosphate on struvite and carbonate apatite formation. Olszynski, Marcin S06-P04 - Investigation of bacterial factors responsible for aggregation process of carbonate apatite. Sadowski, Rafal Robert S06-P06 - Prenucleation clusters - quatarons - and crystal growth. Askhabov, Askhab Magomedovich
7 - In-situ Monitoring ⁄ Control of Crystal Growth Processes ⁄ Crystal morphology S07-P03 - Development of in-situ observation system for high-temperature liquid/solid interfaces: application to solid-source solution growth of AlN. Kangawa, Yoshihiro S07-P06 - Peculiarities of sapphire nitridation under the influence of the high-energy electron beam. Milakhin, Denis Sergeevich S07-P07 - Using modifiers to mitigate salt crystallization damage in porous building materials: an optical microscopy study of borax and sodium sulphate. Granneman, Sanne S07-P08 - Optimization of Cooling Crystallization of High Aspect Ratio Crystals in Batch and Continuous Operations for Size and Shape Control. Acevedo, David S07-P10 - Nanoconfined Crystal Growth investigated by Reflection Interference Contrast Microscopy. Kohler, Felix S07-P12 - Microfluidics for in situ study of growth of calcium carbonate. Li, Lei S07-P13 - In-situ Raman technique applied to monitoring phase transition of linear alkylbenzene sulphonate (LAS). Zou, Boyang S07-P14 - Solubility studies of GaN in NH3/mineralizer-solutions. Steigerwald, Thomas Gottfried S07-P15 - Analysis of temperature data obtained by measurements of temperature field at simulated vertical Bridgman crystal growth of PbCl2. Kral, Robert S07-P16 - Controlling Ice Growth using Selective Infrared Radiation. Guy, Shlomit
S07-P17 - Electron Microscopy Studies of Growth and Structure of MoS2-based Hydrodesulfurization Catalysts.
Hansen, Lars Pilsgaard
8 - Epitaxial Growth - Crystal Growth Interfaces S08-P01 - Impact of boron on the step-free area formation during molecular beam epitaxial growth on MESA structures on Si(111) Roy Chaudhuri, Ayan S08-P02 - Semipolar AlN and GaN on Si(100): concept, HVPE technology and layer properties. Konenkova, Elena Vasilievna S08-P03 - Structure of AlN layer obtained by thermochemical nitriding of (0001) sapphire substrate with terrace-step surface. Vovk, Olena Olexandrivna
S08-P04 - Growth of α-Cr2O3 thin films on α-Al2O3 substrate at low temperature by r.f. magnetron sputtering. Gao, Yin S08-P05 - n-i-p triple junction obtained by the Atomic Layer Deposition method. Gieraltowska, Sylwia
S08-P06 - 2D-islands Nucleation on Si(111) at High Temperature During Sublimation and Thermal Etching by O2. Sitnikov, Sergey
S08-P07 - β-Ga2O3 crystal deposition on sapphire and silicon substrates by chemical assisted vapor transport method. Pechnikov, Aleksei S08-P08 - Dependence of the relaxation of elastic stress on the sign of strain in SiGe epitaxial layers. Novikov, Alexey S08-P10 - Influence of thermal treatment on the optical and electrical properties of ZnO:B thin films. Gritsenko, Lesya Vladimirovna S08-P11 - Preparation and optimization of a molybdenum electrode for CIGS solar cell. Feng, Jingxue S08-P12 - Surface induced weak orientational order and role of isotropic nematic-interface fluctuations in the appearance of an induced nematic film. Pikina, Elena S08-P13 - Effects of thermal annealing on AlInGaN/AlN/GaN heterostructure grown by MOCVD. Ravi, Loganathan S08-P16 - Growth and Optical Investigation on InGaN/GaN Quantum well Structures grown by Metal Organic Chemical Vapour Deposition. Kandasamy, Prabakaran
S08-P17 - Synthesis and thin films growth of BaBiO3, Ba1-xKxBiO3 and BaBiO1-yFz compounds by pulsed laser deposition. Gawryluk, Dariusz Jakub S08-P18 - Properties of Crystalline Silicon Layers for Photovoltaic Application grown on Glass by Steady-State Solution Growth. Ehlers, Christian S08-P19 - CdHgTe deposited on CdZnTe substrates by Closed Space Sublimation technique. Rubio, Sandra
S08-P22 - Growth and luminescent properties of single crystalline films of Ce3+ doped Gd1-xLuxAlO3 and Pr1-xLuxAlO3 perovskites. Zorenko Yuriy
S08-P25 - Strained Ge layers on virtual Si(1-x)Ge(x)(001) substrates. Schmidt, Jan S08-P26 - Reconstruction phase transition c(4x4) - (1x3) on the (001)InSb surface. Bakarov, Askhat
9 - Fundamentals - Structural Defects and their characterization in Crystalline Materials
S09-P03 - Study of charge compensating defects in BaF2:YbF3 crystals using dielectric relaxation” Octavian Bunoiu
S09-P04 - "Some optical properties of YbF3 doped BaF2 crystals"
Octavian Bunoiu S09-P05 - Interplay mechanism of secondary phase particles and the extended dislocations in CdZnTe crystals. Xu, Yadong S09-P06 - Oxygen precipitation behavior in heavily arsenic doped silicon crystals. Porrini, Maria S09-P07 - Blocks and Residual Stresses in Shaped Sapphire Single Crystals. Grigorievich, Nosov Yuri S09-P08. Strain Energy Analysis of Screw Dislocations in 4H-SiC by Molecular Dynamics. Kawamura, Takahiro S09-P09 - Study of defect formation in KDP crystals under high supersaturation. Baskakova, Svetlana Sergeevna
S09-P10 - Czochralski growth and characterization of rare earth-doped Gd3(Al,Ga)5O12 crystals. Ryba-Romanowski, Witold S09-P11 - Nonstoichiometry and luminescent properties of ZnSe crystals grown from the melt at high pressures. Avetissov, Igor S09-P12 - Nonstoichiometry and luminescent properties of tris(8-hydroxyquinoline)aluminum crystals. Avetisov, Roman S09-P13 - Two-dimensional thermoluminescence method for checking crystals homogeneity. Marczewska, Barbara S09-P14 - Disorder control of nanostructural arrangement in AlGaN/GaN light-emitting structures and related phenomena. Shabunina, Evgeniia S09-P15 - Effect of gamma irradiation on the optical properties of CVT grown ZnSe single crystals. Perumal, Kannappan S09-P16 - Thermal stability of ferroelectric domain gratings in Rb-doped KTP. Peña Revellez, Alexandra S09-P17 - Argon ion irradiation effects on CdZnTe crystals: influence of the substrate temperature. Plaza, Jose Luis S09-P18 - On Defects Detection in Crystals using Image Processing and Pattern Recognition Tools. Porat, Moshe S09-P22 - Mystical source of electrically active chlorine at Cl doped CdTe. Sedivy, Lukas S09-P23 - Structural examination of multilayer CrAlN/AlSiN films. Polychroniadis, Efstathios K. S09-P26 - Dislocation mechanism of KDP growth from solution. Alexandru, Horia V.
10 - Nanostructures & Nanoporous Crystals
S10-P01 - Vapour phase catalyst-free growth of β-Ga2O3 nanowires. Calestani, Davide S10-P03 - Bioceramic Coatings Produced on Commercially Pure Titanium by the Induction Heat Treatment and Nanostructure Surface Modification. Fomin, Aleksandr S10-P04 - Metal-Oxide Coatings with Ultrafine Crystalline Structure on Medical Implants Fabricated from Stainless Steel. Fomin, Aleksandr S10-P07 - Growth Mechanism of ZnO Films by Non-vacuum Process at Low Temperature. Yoshino, Kenji
S10-P08 - Low Temperature Growth of Ga-doped ZnO Thin Films Grown by Atmospheric Spray Pyrolysis for CuInGaSe2 Based Solar Cells. Yoshino, Kenji
S10-P10 - Nitride-based self-assembled magnetic nanocrystals and complexes. Capuzzo, Giulia S10-P11 - Growth and Formation of Nanostructures on Metal Surfaces under the Action of Nanosecond Laser Pulses. Mikolutskiy, Sergey Ivanovich S10-P13 - The influence of V/III flow ratio on the self-induced InAs nanowires growth. Sibirev, Nickolay Vladimirovich S10-P14 - Growth and characteristics of InAlAs/AlGaAs quantum dots depending on annealing temperatures. Han, Il Ki S10-P15 - GaN-ZnO Solid solution for photocatalytic applications : Synthesis by Solution Combustion technique and characterization. Menon, Sumithra Sivadas S10-P16 - Cu Catalytic Growth of GaN Nanowires on Sapphire Substrate for p-type behaviour. Kuppulingam, Boopathi S10-P18 - Precursors for CIGSe micro-concentrator solar cells. Eylers, Katharina
S10-P19 - Effect of ZnO/B2O3 ratio on the crystal growth in zinc borosilicate glasses. Kullberg, Ana Teresa
S10-P20 - Synthesis and Characterization of HgI2 Nanostructures for Films Nucleation. Fornaro, Laura
S10-P21 - Synthesis and investigation of hexagonal modification NaY1-x-yYbxEryF4. Mayakova, Mariya Nikolaevna S10-P22 - Hydrothermally Grown Arrays of ZnO Nanorods on Patterned Substrates. Grym, Jan
S10-P23 - Synthesis of BiI3 nanoparticles through hydrothermal method intended for preparing ionizing radiation detectors. Fornaro, Laura S10-P24 - HgS nanostructures for the development of hybrid active layers. Fornaro, Laura S10-P25 - Growth of ZnO nanorods on carbon fibers for in-situ stress measurements. Culiolo, Maurizio S10-P29 - Mass-transport driven growth dynamics of AlGaAs shells deposited by metalorganic vapor phase epitaxy around dense GaAs nanowire ensembles Lovergine Nico S10-P30 - Laser processed oxides for optoelectronics and bio applications. Costa, Florinda Mendes S10-P31 - Obtaining of II-VI compound single crystal substrates with controlled electrical properties and prospects of their application for manufacturing nanotemplates. Colibaba, Gleb V S10-P32 - Surface Morphological Analysis of nano-patterned c-plane sapphire substrates using 450KeV oxygen ions. Jacob, Davis
S10-P33 - Surface modification of Cu2O/p-CuxS thin films for Liquefied Petroleum Gas sensing. Bandara, Kiriwithanage Nayana
11 - Novel Materials and Structures S11-P02 - Growth of p-type ZnOS films by pulsed laser deposition. Kobayashi, Kenkichiro
S11-P04 - On the crystal growth, characterization and magnetic properties of two new phases discovered in the PbO-Fe2O3-P2O5 system. Velazquez, Matias
S11-P05 - Synthesis and structure of perovskite organic-inorganic hybrid of [NH3(CH2)4NH3CoCl4] 1,4 butane diammonium tetrachlorocobaltate.
Abdel-aal, Seham Kamal
S11-P07 - Macro- and microcrystallization of rare-earth aluminum borates in multicomponent systems RAl3(BO3)4 - K2Mo3O10 - B2O3 - R2O3 (R = Y, Gd, Lu). Naprasnikov, Daniil Alekseevich S11-P09 - Structural Characterization of Cobalt Oxide Core-Shell Nanostructure. Lukic-Petrovic, Svetlana
S11-P11 - Low Temperature Growth of Cu2ZnSnS4 Thin Films by Metal Xanthate Precursors. Yoshino, Kenji
S11-P12 - Formation of microcrystalline SrB4O7 :Sm2+ dots in SBO glass-ceramic. Glowacki, Michal Marcin S11-P13 - Form Studies and Thermodynamic Evaluation of Fasoracetam. Harmsen, Bram
S11-P15 - Crystal and electronic structure and magnetic properties of Gd7Pd3 xNix intermetallics. Talik, Ewa S11-P16 - New fluorescent hybrid materials in oxyfluoride glass matrix. Avetisov, Roman S11-P17 - Crystal engineering of molecular salts for single-crystal to single-crystal [2+2] cycloaddition photoreactions. Spinelli, Floriana S11-P18 - Crystallization of a New Calcium Bisphosphonate through Octacalcium Phosphate Digestion. Boanini, Elisa
S11-P19 - X-Ray diffraction and Raman spectroscopy studies of temperature induced phase transitions in Sr3-xCaxFe2TeO9 (0 ≤x≤ 1) triple perovskite. Elhachmi, Abdelhadi
S11-P20 - Growth and structure of single crystal Ba3TaFe3Si2O14 -langasite family multiferroics. Balbashov, Anatoly
S11-P22 - Large GaPd2 single crystals grown by the Czochralski technique. Schwerin, Judith
S11-P23 - Synthesis and crystal growth of NdAl3(BO3)4 with different polytypic structures. Volkova, Elena S11-P24 - 2D transition metal dichalcogenides grown by chloride driven chemical vapor transport. Barreteau, Celine S11-P26 - Influence of polyols on the formation of nanocrystalline nickel ferrite inside silica matrices. Bunoiu, Octavian Madalin S11-P31 - Growth and stability of pinacol hydrates. Sobczak, Szymon S11-P33 - High pressure High temperature (HP / HT) growth of multifunctional perovskites. How chemical substitutions can be used to switch from a magnetoresistive to a dielectric (polar) magnet. Delmonte, Davide
ABSTRACTS
SESSION 1 Fundamentals of Nucleation and Growth Kinetics
Numerical Modelling of Liquid Phase Diffusion growth of SiGe with Uniform Compositions
S. Dost1, M. Sakhon, N. Armour
Crystal Growth Laboratory, University of Victoria, Victoria, BC Canada V8W 3P6
Liquid Phase Diffusion (LPD) is a solution growth technique that was developed as a variant of multicomponent zone melting growth [1]. This technique, where was called “LPD”, was then utilized by [2,3] to grow graded bulk crystals from the germanium side with the objectives of producing seed crystals of desired composition for other growth techniques such as Czochralski and Liquid Phase Electroepitaxy (LPEE). Recently research has been extended where the effects of rotating and static magnetic fields on the transport process were also investigated [4,5]. In these previous studies the LPD growth system was stationary and was subject to an applied temperature gradient. The driving force for growth was the supercooling of the melt due to dissolution of silicon into the germanium melt. Crystals of SiGe were grown with increasing silicon composition along the growth direction. Silicon compositions in the radial direction were uniform.
In the present study, we have carried out new LPD experiments by applying a crucible translation matching with that the solidification rate in order to grow crystals at desired uniform compositions. Determination of optimum translation rate is the issue. In order to shed light into the LPD growth process further we have also carried out numerical simulations of the system. Both constant and dynamic translation rates have been considered. A top-level code is developed in OpenFOAM using a fixed grid approach to model the complete growth process. The process has been simulated by prescribing dynamic thermal boundary conditions along the growth configuration. The numerical solution also reveals a significant reduction in the axial composition gradient in the grown crystal with an additional advantage of shorter growth periods justifying the use of crucible translation as a means to achieve higher compositional uniformity in the grown crystals. Numerical simulations were also carried out, using the commercial code “Fluent”, to examine the benefit of crucible rotation for obtaining better mixing and also for suppressing the initially strong convective flow in the melt. Results showed that a rotation in order of 20 rpm is optimum.
1. Y. Azuma, N. Usami, T. Ujihara, G. Sazaki, Y.Murakami, S. Miyashita, K. Fijiwara, K. Nakajima, J. Crystal Growth, 224 (2001) 204. 2. M. Yildiz, S. Dost, B. Lent, J. Crystal growth, 280 (2005) 151-160. 3. Yildiz, M., S. Dost, and B. Lent, Cryst. Res. Technol., 41(3) (2006) 211-216. 4. Armour, N., and S. Dost, Cryst. Res. Technol., 45(3), 244-248, 2010. 5. Armour N., and S. Dost, Cryst. Res. Technol., 45(4), 335-340, 2010.
1 Corresponding author: [email protected]
An in situ view of nucleation
De Yoreo, James J.*1, Ma, Xiang1, Nielsen, Michael H.2, Chen, Chun-Long1
11Pacific Northwest National Laboratory, Richland, WA 99352, USA 22Department of Materials Science and Engineering, Univ. of California, Berkeley, 94720 USA *email: [email protected]
In the classical picture of nucleation, density fluctuations that are inherent at finite temperature form unstable clusters of the new phase through monomer-by-monomer addition. Clusters transition from being unstable to stable if they exceed a critical size, beyond which the free energy cost of creating the new phase boundary is compensated by the drop in chemical potential. In recent years, hierarchical pathways involving assembly of species more complex than monomers have been proposed for numerous systems. Amongst these, a “two-step nucleation” process was proposed whereby crystals of proteins, other macromolecules, and even simple salts nucleate within monomer-rich, non-crystalline clusters. However, reports of such pathways are almost entirely based on computational models or interpretations of indirect observations. Moreover, little is known about two-step nucleation dynamics and whether the monomers in the clusters are one and the same as those that comprise the crystal nucleus or are act instead to provide an environment for heterogeneous nucleation is uncertain, as is the extent to which these multistep pathways are general features of either macromolecular or inorganic materials. To address these knowledge gaps, we have used in situ TEM and AFM to investigate nucleation in a number of systems. To examine nucleation pathways of macromolecules, we synthesized a biomimetic polymer sequence that forms 2D ordered structures and used in situ AFM to observe nucleation. Our results show that the nucleation occurs along a two-step pathway that begins with creation of disordered clusters containing ~ 10-20 molecules. These clusters transform directly into ordered nuclei that grow via molecule-by-molecule addition, with the kinetics of transformation strongly dependent on Ca2+ concentration. However, when a small aggregation-promoting hydrophobic region is deleted, even though the same final structure is obtained, nucleation occurs in a single step and the nucleation kinetics are dramatically altered. To investigate nucleation of simple inorganic materials, we used in situ TEM to observe nucleation of CaCO3. [1] Formation pathways are confirmed in most cases by collecting diffraction information of the observed phases. We find that amorphous calcium carbonate (ACC), as well as the three predominant crystalline phases: calcite, vaterite, and aragonite, can form directly even under conditions in which ACC readily forms. In addition to these direct formation pathways, we observe two-step nucleation of aragonite and vaterite from ACC. Here, ACC transforms directly to the crystalline phases through distinct nucleation events on or just beneath the surface followed by consumption of the parent ACC particle. The results demonstrate that two-step pathways are possible in both inorganic and macromolecular systems, but are not universal. They can be accompanied by direct nucleation pathways and, in the case of macromolecules, their existence can depend on the specific sequence of the molecule.
References: [1] Nielsen M.H., Aloni, S., De Yoreo, J.J., Science, 345 (2014) 1158.
Homogeneous nucleation in small droplets near critical supercooling
Zdeněk Kožíšek*, Pavel Demo
Institute of Physics of the Czech Academy of Sciences, Cukrovarická 10, 162 00 Praha 6 (Czech Republic) *email: [email protected]
Within standard nucleation model the kinetic equations are numerically solved to determine the size distribution of nuclei in small volumes near critical supersaturation, when first nuclei are formed. The size distribution of clusters, F, in small volumes reaches the stationary value after some time delay and decreases with cluster size i. Supercritical clusters are called nuclei. The size of the largest nucleus i was determined from the condition Fi=1. As a model system we selected recently studied liquid-to-crystal transition in Ni [1] due to available experimental and simulation data. However, using these data leads to the size distribution of nuclei, when no critical nuclei in Ni sample masses from 23 µg up to 63 mg are formed (number of critical nuclei < 1). From this point of view one needs to consider lower interfacial energy σ or to consider the size dependence of σ to increase number of critical nuclei to reasonable level. In larger volume (V=10-9 m3) the radius of the largest nucleus within system r increases with -9 -12 3 time, but at lower volumes (V=10 and 10 m ) nucleus size reaches some extremal size rmax at relative supercooling (TE-T)/TE=0.171, where TE denotes melting temperature (Fig. 1a). This limit of maximum size rmax quickly increases with relative supercooling (Fig. 1b). Critical supersaturation, when first nuclei are detected within system, and also maximum size of nuclei formed within system, depend on the droplet volume. Supercritical clusters continue in their growth only if the number of critical nuclei is sufficiently high. Moreover, in very small volumes nucleation kinetics differs from standard model due to depletion of the parent phase [2]. This work was supported by the Grant No. P108/12/0891 of the Czech Science Foundation.
8 8 a b 7 10-6 7 6 6 5 5
4 (nm) -9 r (nm) 10 4
3 max r 2 3 10-12 1 2 10-9 10-12 0 1 0 0.1 0.2 0.16 0.17 0.18 0.19 t (s) (TE-T)/TE Figure 1. Radius of the largest formed nucleus r as a function of time t (a) and relative supercooling -6 -9 -12 3 (TE-T)/TE (b) for volumes V=10 , 10 , and 10 m .
References: [1] Bokeloh J., Rozas R. E., Wilde G., Phys. Rev. Lett., 107 (2011) 145701. [2] Kožíšek Z., CrystEngComm, 15 (2013) 2269.
Separation of nucleation and growth stages - a way for studying crystal nucleation kinetics and to rule a crystallization process designed to reduce crystal polydispersity
Nanev Christo N.*, Tonchev Vesselin D.
e-mail: [email protected]
Rostislaw Kaischew Institute of Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria Although very simple, the classical nucleation-growth-separation principle, NGSP provides a unique possibility for a direct nucleation study - without ever actually seeing the nuclei themselves: Initially, one rapidly supersaturates a system so that nucleation occurs. To avoid the growth of the arising nuclei, the nucleation period is short. The NGSP was devised due to the principle impossibility to observe elementary acts of crystal nucleation, which proceed at a molecular scale. Therefore, to make nucleated crystallites visible under light microscope the nucleation process is abruptly stopped and the created nuclei are let to grow. This is achieved by rapidly lowering the supersaturation below the upper limit of the metastable zone, i.e. below the threshold limiting the crystal nucleation process. Depriving the system of its capability to further produce nuclei, only the existing super-critically sized clusters are let grow to microscopically visible crystals. Originally, NGSP found application in studying crystal nucleation kinetics: counting the crystals, and plotting their number density, n vs the nucleation time, t, the stationary nucleation rate for the corresponding supersaturation is determined from the linear parts of the curves. Recently, NGSP’s application was broadened; it was used to rule a crystallization process designed to reduce crystal polydispersity, Fig. 1; an internal crystal “seeding” leads to nearly-uniform size insulin crystals, but only after relatively short growth times, till 1 day [1]. With prolonged growth the size scatter augments, despite equally sized crystal “seeds” and the same outer conditions are used. Detailed consideration is given on the inherent trend for increasing polydispersity, in which the emphasis is put on the presence of more active step sources on some of the crystals. Size distributions of the insulin crystals are interpreted retrospectively to give clues concerning the nucleation process itself.
Figure 1. Rhombohedral insulin crystals grown without applying NGSP, and with applying it.
Reference: [1] Nanev C.N., Tonchev V.D., Hodzhaoglu F.V., J. Cryst. Growth 375 (2013) 10-15.
Beams and Blocky Crystals: Another Challenge from the Naica Giant Crystals
Fermín Otálora1*, Joaquín Criado1, Juan-Manuel Garcia-Ruiz1
1Laboratorio de Estudios Cristalográficos. IACT, CSIC/Ugr. Av. Las Palmeras 4, Armilla 18100, Granada (España) *email: [email protected]
The giant gypsum crystals discovered in 2000 in Naica (Mexico) have been since them a source of deep fascination not only because of their spectacular size and look, but also due to the wealth of scientific information that the mineralogical/crystallographic community has got from them. After 14 years of study, [1] one question was still missing in this list of scientific advances triggered by the giant Naica crystals: the origin of two clearly distinct crystal habits for gypsum in the Cave of Crystals, bulky crystals with a morphology close to the equilibrium one [2] or much longer crystals, called “beams”, up to 11 meters long. The coexistence of these two habits so widely different is explained in this communication by a growth rate enhancement at a re-entrant twin angle, where the surface at the atomic scale shows positions similar to growth steps. These positions operate as a source of growth steps additional to any other mechanism, changing the relative growth rate, accelerating the growth of the faces meeting at the reentrant angle and modifying the habit of the twinned crystal [3]. Giant beams in Naica are shown to be 100 contact twins with reentrant twin angles (figure 1a) but the extremely low supersaturation at which the Naica crystals grew makes impossible the laboratory replication of the conditions. The same twins were obtained at higher supersaturation and their growth kinetics analyzed. In these twinned crystals, we checked for the re-entrant angle mechanism as the origin of the elongation of gypsum beams. Figure 1b and c show two sample gypsum crystals growing at the reentrant angle of the 100 contact twin. Figure 1d shows the growth rate measured for the convex and concave sides of the twin, and the growth rate acceleration by a factor of 10 to 30 that results in an elongated habit for these twinned crystals, as proposed for the
Naica giant beams.
Figure 1. The 100 contact twin geometry sketch and a giant Naica Beam showing it (a). Two twinned gypsum crystals growing by reentrant angle growth rate enhancement (b) and (c). The growth rate of the convex (solid squares) and concave (open circles) ends of crystal 1b is shown in (c).
References: [1] Otálora, F. and García-Ruiz, J.M. Chem Soc Rev. 43, (2013) 2013 [2] Massaro, F.R., Rubbo, M. and Aquilano, D. Crystal Growth & Design, 10 (2010) 2870 [3] Kitamura, M., Hosoya, S. and Sunagawa, I. J. Crystal Growth, 47 (1979) 93
Origin of energy efficiency of axial vibration control technique in melt growth process
Evgeny Zharikov, Andrey Sadovskiy, Ekaterina Sukhanova, Vladimir Kostikov, Igor Avetissov*
D. Mendeleyev University of Chemical Technology of Russia, Miusskaya pl. 9, Moscow (Russia) *email: [email protected]
The problem of the effective heat-mass transfer in melt-crystal growth technologies plays a significant role in production of high quality crystals. It was demonstrated that the axial vibrational control technique [1] is one of the most energy efficient technique to manage the melt flows at growth process and govern crystal perfection [2]. The energy induced into the melt by low frequency oscillation of an inert solid baffle (commonly in the form of a disk) could be as high as hundreds joules per mole in a nanosize volume near the disk sharp edge. The melt microstructure evolution under the action of the low-frequency axial vibration control (AVC) technique was studied in situ by Raman spectroscopy and proved by DTA, HT-XRD, DSC measurements [3]. A number of vibrational effects, such as increase of permissible growth rate, distinct alteration of crystallization heat, significant reduction of dislocation density and others are connected with AVC influence on pre-crystallization phenomena and destruction/reconstruction of clusters in the melt at temperatures close to the melting point. In the present research we analyzed the energy efficiency of AVC impact on melt growth process. Fig. 1 demonstrates the influence of the oscillating baffle configuration on the energy induced into the various melts (NaNO3, Ge, CdTe) which significantly differ in viscosity, density, thermal conductivity and specific heat. It was recognized that the disk sharp edge curvature strongly influenced on the induced energy. The numerical simulation was conducted using ANSYS FLUENT 14.5 software and the UDF realizing the disk harmonic oscillation.
Figure 1. Numerical simulation of momentum viscous dissipation in NaNO3 melt activated by oscillation (f=25 Hz, A=0.3 mm) of cylindrical disc with different curvature (R) of a sharp edge
The research was supported by the Russian Foundation for Basic Research grant 13-02-12199.
References: [1] Zharikov E., In: Crystal growth technology. Semiconductors and dielectrics. (Capper P., Rudolph P., eds.), Weinheim: Wiley-VCH Verlag; 2010, p. 41-64 [2] Avetissov I., et. al., CrystEngComm. 15 (2013) 2213 [3] Sadovskiy A., et. al., J. Crystal Growth 417 (2015) 16
Growth of branched rutile-type TiO2 via self-assembly and crystal twinning
Jordan Vanja*1,2, Rečnik Aleksander 1
1Department for Nanostructured Materials, Jožef Stefan Institute, Jamova cesta 39, Ljubljana (Slovenia) 2Jožef Stefan International Postgraduate School, Jamova cesta 39, Ljubljana (Slovenia) *email: [email protected]
Nowadays, mainstream of research in materials science is focused on the novel approaches to synthesize highly branched 3D materials with increased capacity, adaptable morphology, large specific surface area and surface properties tailored for diverse applications [1]. One of the main challenges is understanding crystal nucleation and growth mechanisms, thereby to gain the control for producing desirable branched fractal-like structures (length, width, control of branching events, etc.). With this in mind we focused on studying the most important reaction parameters, including the reaction temperature, precursor and reagent concentration in hydrothermal (HT) synthesis of rutile TiO2. Precursor concentration in the reaction medium (defined as a volume ratio between Ti(IV)-butoxide precursor and HCl: XV) has proved to be the most relevant reaction parameter that influences the nucleation rate and hence the branching of rutile. The highest branching is achieved at the highest XV of 1:33, leading to the formation of rutile microspheres consisted of numerous ultrafine rutile fibers radiating from the common center (Fig.1a), however when XV is decreased to 1:100 the products show fewer but more defined branches where numerous twin incidences and other types of intergrowths can be observed (Fig.1b). High resolution transmission electron microscopy (HRTEM) revealed that the final crystals are growing through the attachment of about 4-5nm thick rutile fibers (Fig.1c) aggregated along {110} planes, with occasional attachments by {101} planes, causing the formation of {101} twins. Twinning relations were confirmed by the selected area electron diffraction across the twin contacts. In crystals oriented in [001]R projection the inherent porous texture can be observed due to imperfect alignment of fibers. On the basis of our experimental results, we propose that the growth mechanism of these highly branched structures is based on crystal aggregation, i.e. self-assembly and more rarely – twinning. Their growth can be divided into three stages: (i) formation of Ti-complexes in the reaction solution, leading to burst nucleation of long rutile fibers when supersaturation is reached (Fig.1c), (ii) aggregation of fibers along {110} and {101} planes through dehydration reactions to form rutile crystals, and (iii) recrystallization that dissolves small nuclei.
Figure 1. (a) Fast nucleation rate when XV is set to 1:33, leads to the formation of highly branched microspheres. (b) With the decrease of XV to 1:100 nucleation rate is slowed down, leading to more perfect attachments during fiber aggregation. Rutile crystals were HT obtained in 7M HCl at 180°C for 3h. (c) HRTEM of rutile fibers roughly aligned along their crystallographic c-axis
References: [1] Cheng C., Fan H.J., Nano Today, 7 (2012) 327-343.
Selective crystallisation of the more stable β polymorph of L-glutamic acid in an acoustic levitator
Rusin Michal1, Ristic Radoljub*1, Gnutzmann Tanja2, Emmerling Franziska2
1Department of Chemical and Biological Engineering, The University of Sheffield, Mappin Street, Sheffield S1 3JD, UK 2BAM Federal Institute for Materials Research and Testing, Richard-Willstaetter-Strasse 11, 12489 Berlin, Germany *email: [email protected]
We observe the nucleation and growth phenomena accompanying the crystallisation of L- glutamic acid (LGA) from its pure solution droplet suspended in an acoustic levitator – an open thermodynamic system. For this purpose, in-situ simultaneous WAXS, Raman spectroscopy and droplet size monitoring techniques were used [1]. Here, we demonstrate, for the first time, that these containerless conditions lead to the nucleation of only stable β form. These observations further demonstrate the sensitivity of crystal nucleation to droplet-air interface structure, the potential of this kind of interface for controlling polymorphism and discovering new polymorphs. In order to get some insight into the above polymorph selection, we compare the subsequent time dependent mole fraction evolutions of the crystallising monomorphic β and dissolved LGA (Fig 1a) with those for dimorphic, typical for closed thermodynamic systems such as batch crystalliser (Fig 1b).
(a) (b)
Figure 1. (a) Mole fraction evolutions in an open thermodynamic system (a levitating droplet) of the selected β phase and dissolved L-glutamic acid (red – β, green – L-glutamic acid in solution). (b) Mole fraction evolutions in a closed thermodynamic system (a butch crystalliser) of the crystallising phases and dissolved L-glutamic acid determined for pure solution (blue – α, red – β, green – L- glutamic acid in solution)
References: [1] Klimakow, M., Leiterer, J., Kneipp, J., Rossler, E., Panne, U., Rademann, K. & Emmerling, F., Langmuir, 26, 11233-11237, 2010.
Enhanced Crystallization Efficiency of an Active Pharmaceutical Ingredient through the Formation of Micron-Sized Crystals in the Undersaturated State.
Bart Rimez*1, Edith Norrant2, Benoît Haut1, Benoit Scheid1
1 Université Libre de Bruxelles - Transfers, Interfaces and Processes (ULB-TIPs), Avenue F.D. Roosevelt 50, 1050 Brussels (Belgium) 2UCB BIOPharma SPRL, Chemin du Foriest, 1420 Braine L’Alleud (Belgium) *email:[email protected]
Particle sedimentations were found in solutions of an Active Pharmaceutical Ingredient (API) and several organic solvents like Methyl Isobutyl Ketone (MIBK), IsoPropyl Acetate (IPAC) and water, seemingly independent of the total solute concentration. Several different analysis techniques pointed out that these particles are formed at temperatures beyond solubility, albeit disappear above the melting temperature of the pure compound (80°C). Dynamic Light Scattering (DLS) tests have shown that these particles can be filtered out of the solutions, after which a new sedimentation takes place. Upon evaluation of these filters after drying, it became clear that the particles do not only consist of API molecules, they are crystalline and have sizes ranging between 1 to 30 m. A SEM image of these particles deposited on a polypropylene filter is shown in figure 1. X-Ray Diffraction experiments showed that the found particles have an identical crystal lattice to the pure API compound in its desired crystal morphology, which is of the cubic type. These findings lead to the development of a fast and efficient way to crystallize this API in the desired crystal form, using microfluidics in the present study. In fact, crystallization will only occur after isothermal treatments in between the solubility line and the melting temperature of the pure API, crystal growth follows then immediately after reaching supersaturated conditions. Depending on experimental conditions, single to multiple cubic crystals can be formed inside microfluidic droplets within short timeframes, discriminating the undesired needle crystals, kinetically more favorable, in favor of the cubic ones [1].
Figure 1. Scanning Electron Microscope image taken of the particle sediment deposited onto a PP filter and dried subsequently.
References: [1] Rimez B., Haut B, Scheid B, Proceedings of the 21st International Workshop on Industrial Crystallization (BIWIC), 2014.
POSTER
S01-P02 Experimental research of phase transitions in a liquid melt of high-purity aluminum
V.B.Vorontsov, V.K.Pershin, M.S.Udintseva
This scientific work is developed to the studying of the genetic connection structures of solid and liquid phases. Based on the results of previous studies [1, 2] cluster formations in the melt - the micro-regions, those retain crystallinity (areas with short-range order of symmetry) were considered as the sours of AE. Fourier analysis of signals of acoustic emission (AE) accompanying melting high purity aluminum from the melting point up to t=860 degrees Celsius was performed. The experimental data allowed to follow the dynamics of disorder zones range order in the melt with increasing melt temperature up to their complete destruction. The presented results of spectral analysis of the signals were analyzed from the standpoint of the theory of cluster melting metals.
Reference
1. V.B.Vorontsov and V.V.Ktalnikov Analysis of acustic emission accompanying metal crystallization: Journal of fhysics, 2008.-p.1-9 2. V.B. Vorontsov, D.V.Zhuravlev, J.Chem.Chem.Eng.6 (2012) 358-362. 3. O.B. Sokolov, l.A.Ugodnikova, Transformation an Fourier Series .In Textbook of metodic, Ekaterinburg, 2005. 4. Aluminum Crystals: experimental Results and Theoretical Model of the Cluster: Journal of Chemistry and Chemical Enginnering, ISSN 1934, USA, 6(2012) 358-362, 20123 j.
S01-P03 On the Theory of Ostwald Ripening: Formation of the Universal Distribution Function in the Presence of Different Mass Transfer Mechanisms
Dmitri Alexandrov*1
1Laboratory of Multi-Scale Mathematical Modelling, Department of Mathematical Physics, Ural Federal University, 620000, Ekaterinburg (Russian Federation) *email: [email protected]
A theoretical description of the concluding stage of Ostwald ripening given by Lifshitz and Slyozov (LS) in the case of diffusion-limited crystal growth [1, 2] and by Wagner [3] in the case of interface-limited growth predicts that after long times the distribution of particles over sizes tends to a universal form. A qualitative behavior of their theory has been confirmed, but experimental particle size distributions are more broad and squat than the classical asymptotic solutions [4]. The origin of discrepancies between the theory and experimental data is caused by the formation and relaxation of solutions from the early to late stages of Ostwald ripening. In other words, the initial conditions at the ripening stage lead to the formation of a transition region near the blocking point of the classical theory and completely determine the distribution function. A new analytical approach developed here on the basis of recently developed theory [5] focuses on the formation process and relaxation dynamics of analytical solutions from the early stage of Ostwald ripening to its concluding state, which is described by the classical asymptotic solutions. An algebraic equation for the boundaries of a transition layer independent of all material parameters is derived. A time-dependent function responsible for the evolution of solutions at the ripening stage is found in the case of different mass transfer mechanisms. Two cases of power-depended and exponentially decaying initial cluster-size distributions are considered. The distribution function obtained is more broad and flat than the classical asymptotic solutions. The analytical solutions obtained are in good agreement with experimental data (figure 1).
Figure 1. The size distribution function P(u) is compared with 20 year experiments [4] (u is the dimensionless size of particles). The solid line shows the LS asymptotic solution whereas the dashed and dotted lines demonstrate the theory under consideration in the case of volume diffusion mass transfer.
References: [1] Lifshitz I.M., Slyozov V.V., Sov. Phys. JETP, 8 (1959) 331. [2] Lifshitz I.M., Slyozov V.V., J. Phys. Chem. Solids, 8 (1961) 35. [3] Wagner C., Z. Elektrochem., 65 (1961) 581. [4] Marder M., Phys. Rev. A, 36 (1987) 858. [5] Alexandrov D.V., J. Phys. A.: Math. Theor., 48 (2015) 035103.
S01-P04 Influence of shear rate on nucleation in oscillation baffled crystallizer
Huaiyu Yang1, Xi Yu2, Vishal Raval1, Yassir Makkawi2, Alastair Florence1,
1CMAC, Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK 2 European Bioenergy Research Institute (EBRI), School of Engineering and Applied Science, Aston University, Birmingham, UK
Induction times of butyl paraben - ethanol solution in batch moving fluid oscillation baffled crystallizer with various experimental conditions e.g. amplitudes (1 - 9 mm) and frequencies (1.0 – 9.0 Hz) and induction times with 2 Hz frequency in continuous oscillation baffled crystallizer, with or without pumping flow, have been determined. The induction time in batch moving fluid oscillation baffled crystallizer increases with increasing amplitude and frequency below 6 Hz frequency and below 6 mm amplitude, i.e. below about 500 power density, because of the increase of the shear rate with increasing of frequency and amplitude. However, the induction time increases with a further increase of the frequency and amplitude. This phenomenon, together with the nucleation behavior of other large or small molecules under shear, may be induced by the mechanism that decreasing size of the steady state of the clusters or density droplets before nucleation. In the continuous oscillation baffled crystallizer with 3 mm or 5 mm amplitude, the interfacial energy and the pre-exponential factor in both high nucleation rate region and low nucleation rate region are determined with or without net flow by Classical Nucleation Theory. The interfacial energy is in good agreement with literatures [1][2]. A Large Eddy Simulation approach in Computational Fluid Dynamics framework [3] is applied to capture the shear rate conditions in oscillatory baffled crystallizers, showing that the shear rate is of spatial periodicity with radially symmetrisation and of temporal periodicity within sinusoidal periodic change of solution’s velocity, and showing that net flow enhances the shear rate at most time in one circulation of the solution’s velocity and Influence of the increasing of the amplitude and net flow, which is consistent with the induction time experiment results in continuous oscillatory baffled crystallizer that the easier nucleation becomes with increase of 2 mm amplitude than with increase of 60 mL/min net flow. COBC MFOBC FBRM or IR
Camera FBRM or IR
Camera Figure 2: Schema of experiment set-up of batch moving fluid oscillation baffled crystallizer (left) and continuous oscillation baffled crystallizer (right)
Figure 1. Induction time with different frequency and amplitude in batch moving fluid oscillatory baffled crystallizer References: [1] H. Y. Yang and A. C. Rasmuson, Cryst. Growth Des., 2013, 13, 4226-4238. [2] J. Liu and Å. C. Rasmuson, Cryst. Growth Des., 2013, 13, 4385-4394. [3] X. Yu, Y. Makkawi, R. Ocone, M. Huard, C. Briens and F. Berruti, Fuel processing technology, 2014, 126, 366-382.
S01-P05 Interferometric Observation of Concentration Field during the Growth of Tetrahydrofuran Clathrate Hydrate in the Guest/Host Boundary Layer
Kazushige Nagashima*1, Hiroaki Goto1, Hiroaki Takahashi1
1Department of Physics, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki 214-8571, Japan *email: [email protected]
Clathrate hydrates have been paid much attention for applications such as storage and transport of natural gas and hydrogen gas, sea water desalination and so on. Typically, gas hydrates such as methane hydrates tend to form a film-like crystal on the surface of water between guest/host phases. The film that separates the gas and water inhibits further growth of hydrates without being stirred to enhance the mass transport. In our previous study [1], growth of tetrahydrofuran (THF) hydrates were observed in THF/water concentration boundary. It was first showed that growth mode transited from the lateral growth of hydrate film along the concentration boundary to continuous nucleation leading to expansion of polycrystalline aggregates into both phases. In the present study, interferometric observation of THF concentration in water was carried out to clarify the effect of mass transport of guest molecules on the hydrate growth in the concentration boundary layer. First of all, the pure water was injected into a vertically arranged growth cell kept at a temperature (= 2.0~3.0°C), which is below the equilibrium temperature (= 4.4°C) of the THF hydrate in the stoichiometric THF water solution (THF-17H2O). Then, THF (liquid) was carefully injected on the surface of water using a micro syringe. Then, contacting the concentration boundary layer with a chilled wire, hydrate crystals were immediately compulsorily nucleated. Without this process, THF and water mix by diffusion. The growth process was in-situ observed using an optical microscope and an interferometer. In addition, the initial thickness of THF/water concentration boundary layer, L, was also observed using the interferometer. L was defined as the region of 1.1~97 wt%, as shown in Fig. 1. Note that the value of L in each run differs from each other, since the water and THF pouring process into the cell mentioned was not completely controlled. This was one of unknown parameters in our previous study [1]. The results showed that when the initial thickness of the concentration boundary layer L was large, the thickness of the growing hydrate film increased. As a result, the lateral growth rate of the hydrate film decreased even at the same THF temperature condition. The expansion rates of polycrystalline aggregates were also affected by L, At large L, the expansion rate of aggregates 97wt% decreased. This suggests that the mass transport 1.3mm through the hydrate film was decelerated by the thick hydrate film caused by the large L. Then, the 1.1wt% results of time dependent areas STHF and Sw of the aggregates in THF and water phases showed that the ratio of STHF to Sw was kept constant throughout
THF concentration Water the run. The ratios obtained in all runs were around 0.15~0.37. This suggests that the same amount of 2mm THF and water were transported per unit time Figure 1. Interference fringes and through the hydrate film. Details will be mentioned concentration distribution of THF in in the conference. water in the initial condition. References: [1] Y. Sabase, K. Nagashima, J. Physical Chemistry B,113(2009)15304-15311.
S01-P06 Study of crystallization processes in Bi-doped As2S3 chalcogenide glasses using linear isoconversion methods
Šiljegović Mirjana, Petrović Dragoslav, Štrbac Goran, Lukić-Petrović Svetlana*
Department of Physics, Faculty of Sciences, University of Novi Sad, Trg Dositeja Obradovića 4, Novi Sad (Serbia) *email: [email protected]
The kinetic analysis of the crystallization processes in Bi-doped chalcogenide glasses was performed using the DSC method. Non-isothermal measurements were carried out at five different heating rates and in the temperature range from room temperature to 773 K. The observed shift of crystallization peak to higher temperatures and the increase of the enthalpy value with heating rate is a result of a well known crystallization rate dependence upon the heat treatment speed. The crystallization process in the sample with 3 at.% Bi was simple with the formation of only Bi2S3 crystallization centers, while in 5 at.% Bi composition the crystallization was a complex thermal process where, in addition to the appearance of Bi2S3 type crystalline centers, the centers of elemental As also occurred. The complexity of this process, and the fact that it takes place at the lower temperatures compared to the crystallization of the sample with 3 at.% Bi, pointed to a lower thermal stability of the Bi5(As2S3)95 glass and higher crystallization affinity.
The activation energy of crystallization (Ea) was determined using Kissinger Akahira-Sunose (KAS) and Ozawa-Flynn-Wall (OFW) methods. Almost twice as high value of the parameter Ea in the sample with the higher Bi content was interpreted by the fact that Bi addition has a growing tendency to significantly modify the amorphous matrix structure through the chain and pyramid structure elements formation. The Ea value for 3 at.% Bi sample does not depend on crystallization fraction volume. In the glass with a higher Bi content reducing activation energy of the first crystallization process was noticed in its final stage, while the second crystallization process was characterized by the continuous increase of Ea with the crystallization fraction volume.
Figure 1. Activation energy of crystallization versus crystallized fraction according to KAS method
S01-P08 Influence of ionic surfactants on sodium chloride crystallization during evaporation Qazi Mohsin Jahan*, Carrier Odile, Bonn Daniel, Shahidzadeh Noushine
Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
Email: [email protected] Sodium Chloride is one of the most abundant salts on earth and its crystallization remains very important in different applications such as degradation and desertification of soils, physical weathering of stones ,degradation of historical monuments , oil well productivity and CO2 storage. On the other hand, surfactants are also widely used as cleaning agents, surface-protection agents, clay-stabilizing agents, oil recovery agents and stone desalination agents, etc. In many of these problems, salt and surfactants are present together in a ternary solution. These form an interesting area of research due to their mutual influence: The concentration of salt can have a direct impact on the surface activity of the surfactant solutions. On the other hand, the surfactants can induce significant kinetic and morphological changes when salts crystallize 1 . In addition it has recently been reported that certain surfactant molecules can be incorporated into the salt crystal lattice, which generates novel composite materials with better mechanical properties 2 . However, the mechanisms by which additives such as surfactants are entrapped in the crystal lattice and how specific features such as their size, structure, charge and concentration affect the crystal lattice remain still poorly understood. The objective of this study is to investigate the crystallization dynamics of NaCl in the presence of a charged surfactant molecule.We have studied the impact of the cationic surfactant (Cetyl trimethylammonium bromide CTAB) on the spontaneous nucleation and growth of NaCl induced by controlled evaporation. First, the physicochemical properties (surface tension, cmc, contact angles) of the ternary systems CTAB-NaCl-water at different concentration of CTAB and NaCl are characterized. Second, the kinetics of nucleation and growth of NaCl crystals was studied during evaporation of CTAB-NaCl-Water solutions in micro-droplets and in glass microcapillaries. This was done using phase-contrast microscopy at controlled relative humidity and temperature 3, 4. The evaporation experiments allow to determine the volume and the concentration of the solution throughout the drying stage. At the end of drying, the crystallization pattern at nanoscale were studied using a High resolution Scanning Electron Microscope combined with an EDS for elemental analysis. Our results reveal a strong interaction between the salt and the surfactant. For the surfactants, the CMC (critical micellar concentrations) behaves non-monotonically as a function of electrolyte concentration. For the salt, changing the concentration of the surfactant leads to different supersaturations at the onset of crystallization, and very different crystal growth kinetics.
References: [1]. Canselier, J. P., J. Disperison Science and Technology, 146 (1993), 625-644. [2]. Yi-Yeoun, Kim et al, Nature Materials, 10, (2011), 890-896. [3]. Desarnaud et al, J.Phys.chem.Lett, 5, (2014), 890-895. [4]. N.Shahidzadeh et al, Scientific Reports,5, (2015), 10335.
S01-P09 A Study of Crystal Growth of Salicylic Acid in Organic Solvents
Jia Lijun*1, Rasmuson Ake1 2
1Materials and Surface Science Institute, Department of Chemical and Environmental Science, University of Limerick, Limerick (Ireland) 2Department of Chemical Engineering and Technology, KTH Royal Institute of Technology, SE-100 44 Stockholm (Sweden) *email: [email protected]
It is hard to overemphasize the importance of crystallization in the pharmaceutical and organic fine chemical process industries. As two main processes of crystallization, crystal nucleation and crystal growth together control the finial crystal product properties. Unfortunately, both kinetics and mechanisms are poorly understood. The type or composition of solvent always influences the crystallization behavior in both nucleation and crystal growth [1]; in our previous work, this influence on nucleation with a simple model compound, salicylic acid, was investigated [2, 3]. In the work here, the crystal growth rate of salicylic acid will be discussed and compared in 4 different solvents, methanol, acetone, ethyl acetate and acetonitrile. The isothermal desupersaturation experiments were carried out in a batch crystallizer for the crystal growth study. FTIR probe was used for the in situ concentration measurement during crystal growth; FBRM probe was used for validating experiment data by detection of nucleation. Figure 1(a) shows the supersaturation decay with time during crystal growth in acetone at a constant temperature 15oC. The empirical power-law equation gives the best fit to the experiment data; from the residual plot in figure 1(b), birth and spread model fits better than the model of BCF.
1.035 o o 0.006 Acetone, 15 C (a)Acetone, 15 C (b) 1.030 Power law Birth & spread Experimental 0.004 1.025 BCF Power law 1.020 Birth & spread BCF 0.002
1.015 0.000 1.010 Residual
1.005 -0.002 1.000 Supersaturation ratio, ratio, S Supersaturation -0.004 0 500 1000 1500 2000 2500 3000 3500 4000 0 500 1000 1500 2000 2500 3000 3500 4000 Time, S Time, S Figure 1. (a) Measured supersaturation ratio versus time together with fitted power law (black solid line), B&S (wine solid line) and BCF (cyan solid line) models. (b)Corresponding residuals based on the three crystal growth models.
References:
[1] R.A. Granberg and Å.C. Rasmuson, AIChE Journal, 51 (2005) 2441. [2] D. Khamar, J. Zeglinski, D. Mealey and Å.C. Rasmuson, Journal of the American Chemical Society, 136 (2014) 11664. [3] D. Mealey, D.M. Croker and A. Rasmuson, CrystEngComm, (2015).
S01-P10 Influence of sintering aid (SiO2) on optical properties of ceramic YAG:Cr,Ca
Vovk Oleh, Chaika Mihail*, Dulina Nadya, Doroshenko Andrey, Parkhomenko Sergei, Tolmachov Olexandr.
Institute for Single Crystals of National Academy of Sciences of Ukraine, Kharkiv, (Ukraine) *email: [email protected]
Ceramic laser materials fabricated by the vacuum sintering technique and nanocrystalline technology [1] have gained more attention as potential solid-state laser materials in recent years. Cr- doped YAG (YAG:Cr) have attracted a great deal of attention because of their potential use as tunable solid state lasers in the spectral range 1.35-1.55 µm or passive Q-switches for laser system based on YAG doped with rare ear ion such as Nd and Yb [2]. In ceramic technology for increasing densification process sintering aids are used. The purpose of this work is to investigate influence of impurity such as SiO2 and CaO on optical properties of ceramic YAG:Cr,Ca. Two series of ceramics were sintered. First contains SiO2, second does not contain SiO2, with different concentration of CaO. Sintering was performed by solid state reaction at 1750 OC for 10 hours in vacuum furnace. Obtained ceramics were investigated with scanning electron microscopy (JEOL JSM-6390LV) and optical spectroscopy (Specord 200). Ceramic YAG:Nd with SiO2, sintered in condition describe above, has grain size distribution from 2 to 50 μm. Ceramics YAG:Cr,Ca with SiO2 and without SiO2 have a similar grain size distribution from 0.5 to 2 μm. Therefore presence impurity CaO in ceramics YAG:Cr,Ca decreased grain grow. Transmission spectra of ceramics YAG:Cr with and without sintering aid SiO2 and different concentration of CaO are presented in Fig. 1. It was shown, that for ceramics YAG:Cr,Ca with SiO2 increasing CaO concentration increases optical transmission. Ceramics without SiO2 demonstrate the existence of optimal CaO concentration. Comparing transmission spectra of ceramics with and without SiO2 clearly show that ceramics without SiO2 have better optical performance than ceramics with SiO2. The possible reason for decreasing optical transmission in ceramics is formation of metasilicate CaSiO3 compound during vacuum sintering. Therefore, sintering aid SiO2, which is widely used in ceramic technology, is not working in system YAG:Cr,Ca.
Figure 1. Transmission spectra of ceramics YAG:Cr,Ca with different concentration of calcium a) with SiO2 b) without SiO2
References: [1] Lu J., Ueda K., Yagi H., Yanagitani T., Akiyama Y., Kaminskii A., J. Alloys Compd., 341 (2002) 220‐225. [2] Yehoshua S., Yehoshua K., Bruce H.T., J. Optical Materials, 4 (1995) 547‐551.
S01-P11 Laser-Induced Nucleation in Continuous Flow
Mackenzie, Alasdair M.*; Pulham, Colin R.; Alexander, Andrew J.
The University of Edinburgh School of Chemistry, Edinburgh (UK) *[email protected]
Continuous flow manufacturing has the ability to change the way pharmaceuticals and fine chemicals are manufactured. Since a steady state can be achieved, a product can be manufactured continuously within certain tolerances. For the understanding of crystallisation change in time can be analysed by measuring different points in space. Implementation has so far faced a problem as to how to reliably generate nucleation in a consistent manner to set t0. Non-photochemical laser induced nucleation (NPLIN) is a technique which initiates nucleation in a fixed irradiated volume over a nanosecond timescale. Experiments using NPLIN can often vary from shot to shot and so many repetitions are needed to accurately describe the phenomenon. This work develops the implementation of NPLIN into a simple continuous flow system for the control of concentration and temperature at the point of irradiation. This enables further studies on nucleation in a repeatable way as well as demonstrating the application of NPLIN for continuous manufacturing.
S01-P13 Understanding of Crystallization and Growth of LiB3O5 crystal in the MoO3- based high-temperature solution at the Molecular Level†
Di Wang*1, Deming Zhang2, Ji Zhang2, Shanshan Liu3, Yinchao Yue3, Guochun Zhang3, Zhanggui Hu3, Shaotang Yin2, Peizhen Fu3, Jinglin Yu4, Mu Wang1
1 Nanjing University, National Laboratory of Solid State Microstructures and Department of Physics, Collaborative Innovation Center of Advanced Microstructures, 22 Hankou Road, Nanjing, China 2 Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Science, 350 Shushanghu Road, Heifei, China 3 Technical Institute of Physics and Chemistry of Chinese Academy of Science, Key Lab of Functional Crystals and Laser Technology of Chinese Academy of Sciences, 29 Zhongguancun East Road, Beijing, China 4Shanghai University, 99 Shangda Road, Shanghai, China *email: [email protected]
In this work, we report experimental and ab initio investigations of the microstructures and molecular dynamic of non-linear optics crystal LiB3O5 grown from the MoO3-based high- temperature solutions. Our results reveal that in the high-temperature solutions of Li2O-B2O3-MoO3 ternary system, molybdenum ions present at polyhedral sites coordinated with oxygen atoms, and the boron-oxygen species are the various six-membered rings containing different BØ4 tetrahedrons (Ø represents the oxygen atom shared between two cations). The molybdenum-oxide polyhedrons and the boron-oxygen networks are not connected with each other, and prefer to be compensated with lithium cations. Therefore, the amount of Li ions can determine microstructures of the high- temperature solutions, and then influence its crystalline habits. Confocued Raman spectroscopy has been used to in-situ investigate the crystal-solution interface around an as-growing LiB3O5 crystal in high temperature MoO3-based solutions. The spectroscopic data has revealed a special growth boundary layer present in front of an as-growing LiB3O5 crystal. In the boundary layer, boron-oxide species transform from structure units of the bulk solution into small lattice-like growth units of the bulk crystal. On the other hand, molybdenum ions change their coordinated numbers and are rejected away from the crystal-solution interface. These structural investigations have suggested the solution near the crystal-solution interface is influenced by the periodic potential of the as-growing crystal surfaces, and the packing configuration of which is reduced with respect to the bulk solution. Based on the obtained structural information, we propose a Li+ cation transfer reaction: to understand growth mechanism of LiB3O5 crystal at the molecular level. Since the key role for the crystal growth, the molecular dynamic in the boundary layer can elucide various crystal growth phenomenon very well, such as the defect formation in bulk crystal, solute-solvent interaction and the phase-equilibria of the Li2O-B2O3-MoO3 ternary system. Our works also indicate that the growth boundary layer around an as-growing crystal provide a new insight into the nature of crystallization and crystal growth mechanism in high-temperature solution.
† National Natural Science Foundation of China (Grant Nos. 51302268, 51472123)
S01-P14 Growth of doped KDP single crystals from solutions with KMnO4 additives
Egorova Anna, Portnov Vadim
1 N.I. Lobachevsky State University of Nizhni Novgorod, 23 Gagarin Avenue BLDG 3, Nizhni Novgorod (Russia) *email: [email protected]
Crystals of potassium dihydrogen phosphate are widely applied in science and techniques, medicine and industry. KDP single crystals were grown using a temperature gradient technique with feeding in a concentration convection regime [1] at a constant solution supercooling of 3.54 C°. We used z- cuts of a large crystal as seeds, and solutions of two compounds: 1) analytical grade potassium dihydrogen phosphate KH2PO4 (KDP) with a concentration of 270 g/L, analytical grade KOH 10 g/L, distilled water and the addition of 20400 mg/L of analytical grade potassium permanganate KMnO4, pH of the solution was 4.7; and 2) KDP 310 g/L, KOH 12 g/L, distilled water and 0200 mg/L of KMnO4, pH=5. We added alkali to prevent crystal thinning. We have found that growth of the (101) faces of a KDP (KH2PO4) crystal is suppressed, and the growth rate of the (100) faces passes through the maximum with increasing addition of KMnO4 to a solution with pH=4.7. MnO2 particles deposit on the (100) faces promoting their growth. The 2+ [MnH2PO4] complexes are adsorbed on the (100) and (101) faces inhibiting the growth up to complete stoppage. The Mn3+ ion substitutes the K+ ion in the crystal structure. The KDP crystals with the growth sectors uniformly doped with manganese were grown in solutions with pH=4.7 and addition of KMnO4. At higher pH, potassium permanganate undergoes chemical transformations in a KDP solution. As a result, the concentration of manganese compounds decreases with time in the bulk solution and, consequently, in the growing crystals. The concentration of manganese in these crystals decreases along the growth directions. The X-ray and electronic paramagnetic resonance data show that manganese is incorporated into the crystal structure in the form of Mn3+ substituting a K+ ion. The optical absorption spectra of KDP solutions with KMnO4 additives and grown crystals have been studied. The effective coefficients of the quadratic non-linear susceptibility of crystal samples with different concentrations of manganese have been measured. The increase of manganese concentration in the <101> growth sectors up to 2.3·105 of the total mass fraction diminishes the effective coefficients of the quadratic non-linear susceptibility.
References: [1] A.V. Belyustin, N.S. Stepanova, Kristallographiya 10 (1965) 743-744.
S01-P15 Study on Growth Kinetics of Partially Deuterated Potassium Dihydrogen Phosphate (p-DKDP) Crystals for High Power OPCPA
Guzman Luis Americo*1, Suzuki Yuta2, Urtnasan Sanduinjud3, Fujimoto Yasushi4, Fujioka Kana5
1National Institute of Technology, Ibaraki College, 866 Nakane, Hitachinaka (Japan) 2National Institute of Technology, Ibaraki College, 866 Nakane, Hitachinaka (Japan) 3Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka (Japan) 4Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita (Japan) 5Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita (Japan) *email: laguzman@chem-ibaraki c-t.ac.jp
Discussions on the future construction of a high intense exa-watt laser, Gekko-EXA with OPCPA amplification system has been started at ILE-Japan. Large single crystals of partial deuterated potassium dihydrogen phosphate (p-DKDP) or K(DxH(1-x))2PO4 are suggested to generate ultra-broad medium for OPCPA [1,2]. The optimum deuterium content in the crystal is estimated to be 50%~80%. Therefore, for the optimal production of large crystals and to satisfy the specified requirements (i.e size and shape) the growth rate of the crystallographic faces need to be studied. In this study, the growth length of the {100} and {101} faces of a single KDP crystal were investigated in partially deuterated (up to 78 mol %) saturated solutions (40℃) in a flow cell at constant supercooling, ΔT=5℃. The crystal size increases linearly in the pure system. While, in the deuterated solution the normalized growth length increases gradually with time as the deuteration concentration increase reaching a maximum growth at 68 mol% D2O. Increasing more yet to a high concentration value 78 mol% D2O, the growth decreases compared to those of low deuterium concentrations. Thus, in some cases relatively lower growth was observed compared to the pure system (Fig. 1). The increased and decreased growth induced by the increased deuterium content in the solution will be explained with the isotopic effect on solubility of KDP crystals in partial deuterated solutions and with the adsorption of some active isotope complexes on the crystal surface causing the step advancement retardation, respectively. We also found that the growth of the {101} face is different than the {100} face and it will be also discussed.
2.5 68 mol% D2O Crystal = KH2PO4 (KDP) Face = {100}
[-] 2 TTs = = 40 40℃℃ G t o ΔT = 5℃
L/G 57 mol% D2O Δ 1.5 47 mol% D2O
78 mol% D2O
1 0 mol% D2O
0.5 Normalized growth lenght lenght growth Normalized
0 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 time [min] Figure 1.Face growth behavior of KDP crystals in partially deuterated solutions.
References: [1] K. Ogawa et al., Optics Express, vol. 17 (2009) 7744-7749. [2] T. Kurita et al., Optics Express, vol. 18 (2010) 14541-14546.
S01-P16 Thinning and thickening of free-standing smectic films
Elena S. Pikina1,2 and Boris I. Ostrovskii3,2
1 11 Oil and Gas Research Institute, Russian Academy of Sciences, Gubkin str. 3, 119333 Moscow, Russia
2 Landau Institute for Theoretical Physics of the RAS, 142432 Chernogolovka, Russia
3 Institute of Crystallography, Russian Academy of Sciences, Leninsky pr. 59, 119333 Moscow, Russia
Smectic liquid crystal is a type of self organization in which elongated molecules are arranged in stacks of liquid layers. When stretched on a frame, these materials can form free-standing smectic films (FSSF) in which the smectic layers align parallel to the two air-film interfaces. Here we present theoretical explanation of the thickness instabilities that occur in FSSF upon changing the external conditions: i) upon heating the film above the bulk smectic disordering temperature, generally the film does not rupture but instead shows successive layer-by-layer thinning transitions;
ii) thickening of FSSF, which occurs within the thermal range of the smectic phase upon local heating. First, we give an overview of the known experimental results. All observations reported so far can be explained on the basis of the Landau-de Gennes theory of the smectic state in combination with nucleation theory. This is well illustrated by the process of preparation of FSSF. Obviously, fabrication of a FSSF is an irreversible thermodynamic process, because nucleation of dislocations is involved. This can be contrasted with ordinary liquids for which the final state of a film is governed by competition between surface tension and gravity, and will be always the same. Then we give theoretical explanation for the thickness instabilities in FSSF [1]. According to our findings, in overheated smectic films (thinning) or locally heated FSSF (thickening) an additional normal tensile force appears due to a change of the mean density of the film. In the case of an overheated FSSF the free energy has oscillatory character, and upon heating the balance of tensile and elastic forces breaks down spontaneously, leading to mechanical instability of the film. The balance can be restored upon spontaneous thinning of the film. Generally a regular series of such thinning transitions occurs, in which the excess layers spills over to the film meniscus. This process necessary includes nucleation and growth of dislocation loops in the middle plane of the film. We determined the thermodynamic conditions for a sequence of thinning transitions and derived expression for the envelope of the actual thinning transition points. Additionally we estimated the characteristic times of dislocation loop growth. The expressions for both the envelope of thinning points and the dynamics of dislocation loops growth are in good agreement with experiments. Local heating of a FSSF within the smectic temperature range induces thermal expansion, which shifts the system to a metastable state. We showed that at relatively large heating (but not too large, to avoid any transition to the nematic or isotropic state) nucleation and growth of dislocation loops of excess smectic layers in the middle plain of the film becomes energetically favorable. At a certain stage of heating, the activation energy for the formation of such dislocation loops becomes smaller than the threshold energy and decreases upon further heating. This leads to local film thickening by many tens of layers. The realization of this scenario crucially depends on the energy dissipated locally in the film. Estimates of the thickness of the growing “island” in the film and of the velocity of the dislocation loop growth are in reasonable agreement with experiments [2].
1. E. S. Pikina, B. I. Ostrovskii and W. H. de Jeu, Eur. Phys. J. E 38: 13 (2015). 2. W.H. de Jeu, A. Fera, B.I. Ostrovskii, Eur. Phys. J. E 15, 61 (2004).
S01-P17 In-situ SAXS studies of crystal structures of C16/C18 binary system during crystallisation and phase transformations in melts
Xue Tang*1, Xiaojun Lai1, Kevin J. Roberts1 Ken Lewtas2 and Iain More2
1Institute of Particle Science and Engineering, School of Chemical and process Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom 2Infineum UK Ltd, Milton Hill Business and Technology Centre, Abingdon, OX13 6BB, UK
Understanding the crystallisation of C16H24 and C18H38 alkane solution is very important to ensure trouble-free operation in diesel fuels [1]. However, for the binary mixtures of C16H24 and C18H38, the crystallisation transition behaviour and resultant structures, as a function of their compositions has not been clearly defined [2]. These structural changes are best examined by in-situ SAXS studies using synchrotron radiation to characterise the early molecular scale aggregation stage prior to the crystallisation and to probe a fundamental perspective for their self-assembly into clusters and nuclei and the subsequently into 3D ordered crystal structure.
MSZW has been determined by DSC measurements performed on 11 binary mixed samples of C16H24 and C18H38 varied 10% of molecular weight of C18H38. This work also characterised the phenomenon of these binary mixtures crystallising via some rotation phases from high temperature region and then transferred into some stabilized crystallographic phases around the low temperature region.
SAXS studies at the beamline X27C in NSLS using a poly-thermal cooling crystallisation process at 0.1 °C/min from 35 °C to 10 °C were also carried out. Examination of the data shows an increase in the slope of scattering intensity as a function of the q range from 0.007-0.2 Å-1 consistent with a change in molecular ordering prior to crystallisation, followed by a much more abrupt change at the crystallisation onset. This gives the evidence of the possibility to apply the in- situ SAXS technique associated with the examination of crystallisation process.
[1] D.L Klass., Biomass for renewable energy, fuels, and chemicals. 1998: [2] E B. Sirota, et al., The Journal of Chemical Physics, 1993, 98(7), pp.5809-5824.
S01-P18 Solution state studies of C16H24/C18H38 binary system in dodecane from poly-thermal crystallisation process
Xue Tang*1, Xiaojun Lai1, Kevin J. Roberts1 and Diana M. Camacho Corzo1 Ken Lewtas2 and Iain More2
1Institute of Particle Science and Engineering, School of Chemical and process Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom 2Infineum UK Ltd, Milton Hill Business and Technology Centre, Abingdon,OX13 6BB, UK
Studies of solution behaviour of binary mixtures of normal alkanes C16H24/C18H38, the dominant component of biofuels derived from hydrogenated vegetable oils (HVO)1 have been examined by a poly-thermal cooling crystallisation process. Saturation temperatures and MSZW have been measured for the n-alkanes C16H24 and C18H38 and for their 9 binary mixtures in different molar ratios from n-dodecane solvent. Saturation temperatures are found to reflect the higher lattice stability as showed in Fig 1 below. The decrease in saturation temperature observed over the temperature rangefor 0.1 to 0.4 C18H38 in C16H24 mixtures is due to the formation of some phases with higher solubility and hence lower lattice stability than that of the triclinic phases of single C16H24 or C18H38. Equilibrium solubility of each composition is also used to perform Van ’t Hoff plot with calculated ideal solution activity. The corresponding activity coefficients for all mixtures for 11 binary mixtures in n-dodecane solvent dhowed negative deviation to ideal solutions, with the pure solutes of C16H24 and C18H38 generally more close to the ideal condition with smaller values of activity coefficient (γ). The equimolar mixture (0.5C16H24/0.5C18H38) shows the largest values from 1.95-2.55 indicates the largest deviation from the ideal activity.
[1] R. G. Mason and H. L. Rice, 1979. Hydrogenated vegetable oil. Google Patents.
S01-P19 Nucleation of amine soaps
Booth, David R.*1, Lai, Xiaojun1, Robles, Eric2
1Institute of Particle Science and Engineering, University of Leeds, LS2 9JT, UK 2Procter & Gamble Newcastle Innovation Centre, Newcastle, NE12 9TS, UK *email: [email protected]
Amine soaps are used as surfactants in a broad range of products. The most commonly encountered amine soaps are alkanolammonium carboxylates. Despite their widespread use, there is little information available in literature regarding their phase behavior especially compared to their sodium soap equivalents [1, 2]. The information that is available focuses on their behavior above the Krafft boundary and doesn’t give any insight into their precipitation or crystallisation below the Krafft boundary. This present study has determined the metastable zone width for four different alkanolammonium carboxylate-water systems, focusing on the micellar region of the phase diagram (<20% wt soap). Monoethanolamine was used to produce soaps of the following saturated fatty acids; lauric (C12:0), myristic (C14:0), palmitic (C16:0), stearic (C18:0). The metastable zone width was determined using polarized optical microscopy, turbidity measurements, and DSC. The precipitate was studied using simultaneous SAXS and WAXS to distinguish crystals from liquid crystals. The nucleation kinetics of the soaps were compared using Nyvlt’s approach as the observed kinetics were a combination of the crystallization kinetics and the kinetics of the dissolution of micelles. The obtained nucleation orders were compared with those already available in literature for the equivalent sodium soaps [3]. The monoethanolammonium soaps showed the same trend as their sodium equivalents of decreasing nucleation orders with chain length.
References: [1] Zhu, S. et al. J Phys Chem B. 109(2005),11753. [2] Warnheim, T. and Jonsson, A. J Colloid Interface Sci. 138(1990), 314. [3] van Gelder, R.N.M.R. et al. J Cryst Growth. 166(1996), 189.
S01-P20 Nucleation, crystal growth kinetics and morphology of methyl stearate as a function of solution environment
Camacho Corzo Diana Milena*1, Roberts Kevin J1, Thomas Danielle1, Lewtas Ken2, More Iain2
1Institute of Particle Science and Engineering and Institute of Process Research and Development, School of Chemical and Process Engineering, University of Leeds, Leeds, LS2 9JT, UK 2Infineum UK Ltd, Milton Hill Business and Technology Centre, Abingdom, OX13 6BB, UK *email:[email protected] The nucleation, crystal growth kinetics and morphology of methyl stearate crystallising from three different solvents: n-dodecane, kerosene and toluene is analysed. A polythermal methodology is used in connection with the recently proposed KBHR (Kashchiev, Borissova, Hammond, Roberts) model [1, 2], to assess the mechanisms and the kinetics of nucleation of methyl stearate crystallising from solutions with concentrations ranging from 200 to 350 g/l. The analysis reveals in all cases a progressive nucleation mechanism and crystallite interfacial tension values between 0.94-1.55, 1.21 - 1.91 and 1.16-2.27 for methyl stearate crystallising from n-dodecane, kerosene and toluene respectively. Nucleation rates calculated using the obtained values of and the number of crystals at the detection point range between 2.6 x 1014 and 4.9 x 1015 , with the highest rates predicted for methyl stearate crystallising from n-dodecane solutions. A detailed analysis of the crystal morphology for methyl stearate, using a methodology based on a combined BFDH and zone axis analysis [3] yields the morphological indexation to be <111> based on the expected orthorhombic crystal structure. Crystals growing from supersaturated n-dodecane, kerosene and toluene solutions, as study using in-situ optical microscope, at supersaturation (σ) levels of 0.3-0.42, 0.45-0.52 and 0.04-0.08 respectively, reveal that the crystal morphology changes only in the case of methyl stearate crystallising from kerosene at the lowest supersaturation values. The growth rates measured in toluene for the (1-11) face are of the same order of magnitude to those observed in kerosene, ranging from 0.02 to 0.37 and are around half those observed in n-dodecane solutions, in which these values range from 0.09 to 0.82 . Measurements of the growth for the (111) face in the case of kerosene solutions, are much lower in magnitude compared to those for the (1-11) face, ranging from 0.01 to 0.15 , which gives these crystals an elongated lozenge shape. On the other hand, similar growth rates values are observed between the (111) face and the (1-11) face for crystals growing from n-dodecane and toluene solvents, ranging from 0.11 to 1.05 and 0.04 to 0.35 respectively. The tendency of the growth rates dependence on σ is consistent with a Birth and spread (B&S) growth mechanism for growth from n-dodecane and with a BCF mechanism for growth from kerosene and toluene solvents.
References: [1] D. Kashchiev, A. Borissova, R.B. Hammond, K.J. Roberts, Dependence of the Critical Undercooling for Crystallization on the Cooling Rate, J Phys Chem B, 114 (2010) 5441-5446. [2] D. Camacho, A. Borissova, R. Hammond, D. Kashchiev, K. Roberts, K. Lewtas, I. More, Nucleation mechanism and kinetics from the analysis of polythermal crystallisation data: methyl stearate from kerosene solutions, Crystengcomm, 16 (2014) 974-991. [3] D. Camacho, K.J. Roberts, K. Lewtas, I. More, Nucleation, Crystal Growth Kinetics and Morphology of Methyl Stearate as a Function of Solution Environment, Journal of Crystal Growth, 10.1016/ j.jcrysgro.2015.01.006.
S01-P21 Metastability limit for the nucleation of NaCl crystals in confinement Julie Desarnaud1, Hannelore Derluyn2.3, Jan Carmeliet3, Daniel Bonn1, Noushine Shahidzadeh1
1University of Amsterdam, Institute of Physics, Science Park 904, 1098 XH Amsterdam (The Netherlands) 2University of Ghent, Department of Geology and Soil Science – UGCT Krijgslaan 281 S8, 9000 Gent, (Belgium) 3ETH, Institut für Technologie in der Architektur, HIL E 46.3, Wolfgang-Pauli-Str. 15, 8093 Zürich (Switzerland) *email: [email protected]
Crystallization in porous media is very important in many applications such as oil recovery, civil engineering, soil mechanics and protein purification: for civil engineering and geology, salt crystallization, is one of the major causes of mechanical or physical weathering causing disintegration of rocks and building materials [1-2] . Moreover, salinisation and sodification are a serious form of soil degradation causing desertification of soils in Europe. For proteins, it was also shown recently that the nucleation of protein crystals on mesoporous materials can be a very promising avenue for protein crystallization [3,4]. For most if not all of the above-mentioned applications, the precise conditions under which NaCl crystals nucleate and growth from solution are very important but largely unknown..
We have investigated the spontaneous nucleation and growth of NaCl crystal induced by controlled evaporation in confined geometries (microcapillary) spanning several order of magnitude in volume[7]. Our results show that supersaturation achieved at the onset of spontaneous primary nucleation and growth is around 1.6 and remains independent of the size, shape, and surface properties of the microcapillary. We show from classical nucleation theory that this is expected: S~ 1.6 corresponds to the point where nucleation first becomes observable on experimental timescales. A consequence of the high supersaturations reached at the onset of nucleation is the very rapid growth of a single skeletal (Hopper) crystal [5]. Experiments on porous media (sandstone) also reveal the formation of Hopper crystals in the entrapped liquid pockets in the porous network and consequently underline the fact that sodium chloride can easily reach high supersaturations, in spite of what is commonly assumed for this salt.
Spontaneous growth of Hopper crystals at supersaturation S∼ 1.6, in a square microcapillary (50 m)5.
References: [1]. . Shahidzadeh-Bonn N, Desarnaud J., Bertrand F., Chateau X., Bonn D., Phys. Rev. E. 81, (2010), 066110. [2]. N.Shahidzadeh and J.Desarnaud, Eur. Phys. J. Appl. Phys. 60, (2012), 24205. [3]. A.J.Page and R.P.Sear, JACS, 131, (2009), 17550. [4]. Diao Y., Harada T., Myerson A.S, Hatton T., Trout B.L., Nature materials, 10 (2011), 867- 871. [5]. Desarnaud J., Derluyn H. , Carmeliet J., Bonn D., Shahidzadeh N., J. Phys. Chem. Let. 5, (2014) 890-895.
S01-P22 The role of alanine, aspartic acid and lysine as simple models of organic matrix molecules participating in calcium carbonate biomineralization
L. Štajner, D. Kralj
Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia
Calcium carbonates could be biomineralized by different invertebrate organisms, either in a form of certain polymorph (calcite, vaterite and aragonite) or hydrated modification. The formation of specific crystal modification or appearance of appropriate morphological form can be influenced by parameters like temperature, pH or supersaturation, as well as by the presence of inorganic components or biomolecules. At that, the important organic components of extrapallial fluids, in which the biomineralization takes place, are proteins. Previously, the influence of isolated fragments of proteins extracted from mineralized tissues, or their synthetic macromolecular analogues has been investigate in the appropriate calcium carbonate model systems.1, 2 ,3
The aim of this research is to investigate the influence of amino acids, selected as simple models of biomacromolecules supposed to be responsible for nucleation, growth and transformation of calcium carbonates in biomineralizating systems. For that purposes, alanine (Ala), lysine (Lys) and aspartic acid (Asp) were used. Besides their chemical differences, at the conditions applied in the selected model systems the used amino acids have different net charges as well: Ala is neutral, Lys is positive and Asp is negatively charged. The results of potentiometric, spectroscopic, chemical, structural (PXRD) and microscopical (SEM) analyses indicated the overall inhibition of calcite precipitation in the presence of Lys and Aps, that (inhibition) is probably caused by slower transformation of initially formed vaterite, into calcite.4 Since both amino acids are charged at applied experimental conditions, some non specific surface interactions are assumed to be responsible for observed effect. The additional kinetic experiments and molecular modelling will be necessary to reveal the nature of respective intermolecular interactions.
[1] A. Adamiano et al, (2012) Chem. Eur. J 18 14367 – 14374.
[2] B. Njegić-Džakula et al., (2013) Croat. Chem. Acta 86 39–47. [3] .B. Njegić Džakula et al., (2009) Cryst. Growth Des. 9 2425-2434.
[4] D. Kralj et al., (1997) J. Cryst. Growth 177 248-257.
S01-P23 Crystallization kinetics of iron inclusion in magnesium aluminosilicate glass processed by laser floating zone technique
Nuno M. Ferreira1*, Andrei V. Kovalevsky2, Manuel A. Valente1, Nikolai A. Sobolev1, João C. Waerenborgh3, Jorge R. Frade2, Florinda M. Costa1
1 Department of Physics, i3N, University of Aveiro, Portugal 2 CICECO – Aveiro Institute of Materials, Department of Materials and Ceramic Engineering, University of Aveiro, 3810-193 Aveiro, Portugal 3 Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa, 2695-066 Bobadela Lisboa, Portugal *email: [email protected]
Magnesium aluminosilicate (MAS) glasses were proposed as a base molten electrolyte for iron pyroelectrolysis, an alternative electrometallurgical technique which offers prospects for environmental and economic advantages over traditional steelmaking [1,2]. This work is focused on the assessment of mechanisms for iron incorporation in the MAS glass system and related effects on their physical properties [3-5]. Faster pulling rates were found favorable for the formation of isolated iron cations in the glass forming network. The crystallization process (slower pulling rates), accompanied with separation of mullite and cordierite-type phases, is strongly affected by the formation of nanosized iron-containing clusters, confirmed by Mössbauer and EPR spectroscopies. LFZ method shows good prospects for studying the crystallization mechanisms in silicate-based glasses with additions of redox-active cations, by providing flexibility in tuning their oxidation state and attaining frozen-in conditions.
References: [1] – N.M. Ferreira, A.V. Kovalevsky, S.M. Mikhalev, F.M. Costa, J.R. Frade, Prospects and challenges of iron pyroelectrolysis in magnesium aluminosilicate melts near minimum liquidus temperature, Phys. Chem. Chem. Phys., 17 (2015) 9313-9325. Doi: 10.1039/c5cp00858a [2] – N.M. Ferreira, A.V. Kovalevsky, J.C. Waerenborgh, M. Quevedo-Reyes, A.A. Timopheev, F.M. Costa and J.R. Frade, Crystallization of iron-containing Si-Al-Mg-O glasses under laser floating zone conditions, J. Alloys Comp. 611 (2014) 57–64. [3] – I. Fanderlick, Silica glass and its application, Elsevier Science Publishers: Amsterdam, 1991. [4] – B. Mysen, P. Richet, Silicate glasses and melts: properties and structure, Elsevier: Amsterdam, 2005. [5] – A. Mekki, Magnetic Properties of Fe ions in a silicate glass and ceramic, Phys. Status Solidi A 184 (2001) 327–333.
S01-P24 The NMR study of 3He enclosed in nanotubes MCM-41
Mikhin Nikolay, Birchenko Oleksandr, Fysun Yana*1
1B.Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, 47 Lenin Ave., Kharkov 61103 (Ukraine) *email: [email protected]
MCM-41 is a mesoporous molecular sieve of SiO2. It consists of a uniform array of parallel quasi-1D straight honeycomb mesopores. It is a powder sample where the pore length is equal to the grain size of 300 nm. MCM-41 can be produced with a variety of different pore sizes. In our case a pore diameter is about 2.5 nm. At low temperatures (T <10 K) the powder MCM-41 is effective adsorbent of noble gases (in our case – helium-3) with good absorbency (specific surface area ~ 1000 m2/g). Moreover, 99% of the adsorbing surface is the inner surface of the tubes [1]. It has known that roughly first 1.8 monolayers of adsorbed helium have the structure of disordered solid [2]. Next additional portions of 3He have the properties of a “rarefied" liquid. This quasi-one-dimensional object is supposed to have properties of Tomonaga-Luttinger liquid, low-dimensional structure of the 3He fermions [3] 3He adsorbed in 0.4 cm3 of MCM-41 powder was investigated by pulse NMR method (ω0/2π=9.15 MHz). Spin-lattice T1 and spin-spin T2 relaxation times, as well as D spin-diffusion coefficient were measured in the temperature range 1.3-2 K. It was found at least two different contributions to the NMR signal, which can be associated with “disordered solid” and “rarefied liquid” phases of 3He mentioned above. The results obtained in the experiments are discussed
References: [1] C. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359, (1992) 710 [2] N. Wada,·T. Matsushita,·M. Hieda,·R. Toda, J. Low Temp Phys 157, (2009) 324 [3] B. Yager, J. Nye´ki, A. Casey, B. P. Cowan, C. P. Lusher, J. Saunders, PRL 111, (2013) 215303
S01-P25 Block copolymer aggregates on planar substrates: Impact of preparation conditions and surface wettability
José Danglad Flores*, Hans Riegler
Max-Planck-Institute of Colloids and Interfaces, Am Mühlenberg 1 OT Golm 14476, Germany *email: [email protected]
Block-Copolymer solutions (PS-PMMA-toluene) are spin cast onto planar surfaces. Meanwhile the spin casting process; the film thinning due to the hydrodynamic-evaporation has been understood quantitatively [1]. The thinning film may eventually dewet into droplets. This dewetting depends on a) the spin casting conditions (speed, temperature, evaporation rate, etc.); b) the initial PS-PMMA concentration, and c) the substrate surface wetting properties. We investigate (by AFM) how a) the preparation process (spin casting parameters), b) the global surface wetting properties, and c) the local surface wetting properties (nano-patterned surfaces) affect the resulting PS-PMMA aggregate morphology. Thus we want to eventually control and manipulate the resulting self-assembly block copolymer patterning.
Graphical Abstract. Different morphologies of block-copolymer aggregates on different substrate surfaces: a) on an Alkychlorosiloxane-coated surface [2], b) on a baked thin film of block-copolymer[3], c) on silica[4].
Reference
1. Karpitschka, S., C.M. Weber, and H. Riegler, Spin casting of dilute solutions: Vertical composition profile during hydrodynamic-evaporative film thinning. Chemical Engineering Science, 2015. 129(0): p. 243-248. 2. Peters, R.D., et al., Wetting Behavior of Block Copolymers on Self-Assembled Films of Alkylchlorosiloxanes: Effect of Grafting Density. Langmuir, 2000. 16(24): p. 9620-9626. 3. Bang, J., et al., Facile Routes to Patterned Surface Neutralization Layers for Block Copolymer Lithography. Advanced Materials, 2007. 19(24): p. 4552-4557. 4. Buck, E. and J. Fuhrmann, Surface-Induced Microphase Separation in Spin-Cast Ultrathin Diblock Copolymer Films on Silicon Substrate before and after Annealing. Macromolecules, 2001. 34(7): p. 2172-2178.
S01-P26 Switching off Non photochemical laser induced nucleation by use of nanofiltration Thomas Kendall*1,2, Dr Nadeem Javid1, Dr Iain Burns1, Prof Jan Sefcik12. University of Strathclyde1, James Weir Building 75 Montrose Street, Glasgow (UK) CMAC2, Technology and Innovation Centre Level 6, 99 George Street, Glasgow (UK) [email protected]
We have investigated the effect of nanofiltration on non-photochemical laser induced nucleation (NPLIN) in order to provide better understanding of underlying nucleation phenomena. We used linearly polarized nanosecond pulsed laser light of wavelength 1064 nm to irradiate glycine solutions at various supersaturations (1.4-1.6) under isothermal conditions. The nucleation behaviour showed strong supersaturation dependence in terms of probability distribution of nucleation induction times, where the nucleation probability increased systematically with increasing supersaturation as expected. Surprisingly, a bimodal distribution of nucleation induction time was observed in unfiltered solutions, with a first relatively fast regime followed by a second slow regime for all supersaturations studied. The nanofiltration of the undersaturatred solutions before their cooling to the desired crystallisation temperature resulted in drastically reduced nucleation probability and only the second slow regime of nucleation distribution was observed across all the supersaturations. This suggests that the filtration removed nanoscale nucleation prone moieties from solutions which interact with laser to induce nucleation. When solutions were investigated with dynamic light scattering we found there was a reduction in both the size and intensity of solute mesoscale clusters which suggests a possible link between these solute clusters and NPLIN. We also investigated the effect of irradiation on polymorphism for unfiltered solutions at different supersaturations: the lower supersaturation (1.4) predominantly yielded α polymorph and higher supersaturations (1.5 and 1.6) showed enhanced γ polymorph nucleation (41 % crystals were γ form). The filtered solutions (both irradiated or non-irradiated) nucleated predominantly as α polymorph. We therefore hypothesize that the glycine mesoscale clusters play a major role in laser induced nucleation and polymorph control in aqueous glycine solutions.
Figure 1. Cumulative distribution of induction times for laser induced nucleation in filtered & non-filtered and irradiated & non-irradiated glycine aqueous solutions (supersaturation 1.6)
SESSION 2 Theory and Modeling Collaboration of atomic and macro scale calculations: polytype and defect control of wide ba111ndgap materials
Koichi Kakimoto*1, Bing Gao1, Shin-ichi Nishizawa2, Satoshi Nakano1, Yoshihiro Kangawa1
1 RIAM, Kyushu University, 6-1, Kasuga-koen, Kasuga, Fukuoka, (JAPAN) 2 AIST, 1, Umezono, Tsukuba, Ibaraki, (JAPAN) *email:[email protected]
Modeling of crystal growth by numerical method plays an important role to predict phenomena in macro- and microscopic point of views. This paper focuses on the process of crystal growth of SiC by physical vapor transport. Crystal growth of a certain polytype of SiC in a process of physical vapor transport was studied on the basis of classical thermodynamic nucleation theory in conjunction with numerical results obtained from a macroscopic global model. Formation of a certain polytype in the nucleation stage is determined by the energy balance among surface energy which is obtained by the first principle calculation in an atomic scale, formation energy and supersaturation. The preferential growth condition of a certain polytype was estimated. The value of super saturation was estimated using a numerical model obtained by a global model that includes species transport as well as heat transport in a furnace. The results of calculation showed that 4H- polytype is mores table than 15R, 6H and 3C-polytypes. Free energy difference between 4H- and 6H-polytypes decreased when total pressure in the furnace decreased [1-3]. The effect of nitrogen and aluminum as doped impurities on the stability of SiC polytypes (C- or Si-face 4H and 6H substrates) formed by physical vapor transport (PVT) was investigated. The results reveal that the formation of 4H-SiC was more stable than that of 6H-SiC when a grown crystal was doped with nitrogen using C-face 4H- and 6H-SiC as seed crystals. In contrast, formation of 6H-SiC was favored over 4H-SiC when Si-face 4H- and 6H-SiC seed crystals were used. Meanwhile, the formation of 4H-SiC was more stable than that of 6H-SiC when aluminum was the dopant and C- and Si-faces of 6H-SiC were used as seed crystals. Formation of 6H-SiC occurred over that of 4H-SiC in the cases of C- and Si-faces of 4H-SiC as seed crystals. To dynamically model the plastic deformation of 4H–SiC single crystals during physical vapor transport (PVT) growth, the Alexander–Haasen model, originally proposed for the elemental semiconductor, is extended into IV–IV compound semiconductors. By fitting the model parameters to the experimental data, we show that the Alexander–Haasen model can describe the plastic deformation of 4H–SiC single crystals if the activation of the carbon-core partial dislocation is modeled in the high-temperature region (above1273 K) and the silicon-core partial dislocation is modeled in the low-temperature region (below 1273 K). We then apply the same model to the dynamical deformation process of a 4H–SiC single crystal during PVT growth. The time evolution of the dislocation density is shown, and the effects of the cooling time on the final dislocation density, residual stress and stacking faults are also examined [4-7].
References: [1] K. Kakimoto, et al., J. of Crystal Growth, 324 (2011) 78. [2] T. Shiramomo, et al., J. of Crystal Growth, 352, (2012) 177. [3] T. Shiramomo, et al., J. of Crystal Growth, 385, (2014) 95. [4] Bing Gao and Koichi Kakimoto, Cryst. Growth Des., 14 (2014) , 1272. [5] Bing Gao, et al., J. of Crystal Growth, 386, (2014) 215. [6] Bing Gao, et al., J. of Crystal Growth, 392, (2014) 92. [7] Bing Gao, et al., J. of Crystal Growth, 396, (2014)7.
Gaining understanding of crystal growth processes via modeling: Pushing the continuum from the top down Yutao Tao, Andrew Yeckel, and Jeffrey J. Derby*
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, U.S.A. *email: [email protected]
From a modeling and simulation perspective, crystal growth processes represent some of the most complex and challenging systems ever analyzed, requiring a multidisciplinary and multi-scale approach and drawing on a wide range of scientific and engineering expertise. This lecture will describe continuum transport processes at play during crystal growth from a mathematical and computational modeling perspective. Recent results from research studies will be used to illustrate these modeling concepts. In particular, we will discuss models for the interactions of solid particles with a moving solid- liquid interface, focusing on silicon carbide (SiC) particles in multi-crystalline silicon. We present a continuum model that allows for a rigorous representation of forces across disparate length scales, including van der Waals interactions arising from atomistic effects. We demonstrate how this model is able to represent large deformations of the melt-solid interface during the process of engulfing a solid particle that is on the order of 1-10 microns in size. Of particular interest is the inclusion of a physically motivated, pre-melted liquid layer in the problem formulation. Our finite-element representation permits nanometer-scale resolution of this layer, which, importantly, circumvents the use of arbitrary cut-off values for determining minimum gap thickness prior to particle engulfment. We present validation of our approach by comparison to select analytical results and to ongoing experiments of the ParSiWal project, funded by the German DLR and involving the Fraunhofer IISB, University of Freiburg, and University of Bayreuth. We address the critical factors that determine the transition from the stable pushing of a particle by a solid-melt interface to conditions where engulfment is inevitable. Of particular interest and relevance is the discovery that oscillating solidification fronts, as would arise due to turbulent fluctuations in large-scale silicon melts, can drive engulfment of silicon carbide particles at average growth rates far below those predicted by prior steady-state analyses.
Figure 1. Computation of a SiC particle engulfed by solidifying silicon. (a) Snapshot of finite element mesh used in this calculation, with particle and solidification front indicated in red. (b) System geometry, with solute concentration field (left) and temperature contours (right). Our model accurately resolves a thin, premelted liquid layer, on the order of nanometers in thickness. ______This research was supported in part by U.S. National Aeronautics and Space Administration, NNX10AR70G; no official endorsement should be inferred.
Study on the usage of a commercial software (Comsol multiphysics®) for
dislocation multiplication model
B. Gallien, M. Albaric , J.P. Garandet, T. Duffar, K. Kakimoto , M. M’Hamdi *email: [email protected]
Keywords: dislocation density, plasticity, numerical simulation, photovoltaic silicon,
Elaboration of silicon ingots for photovoltaic application in Directional Solidification furnace leads to formation of defects in crystal lattice. Among these defects which impact photovoltaic conversion rate, there are dislocations, linear defects due to stresses. Several teams around the world have created numerical simulation using home-made software in order to study dislocation multiplication and predict the dislocation density inside ingots during elaboration.
In this study, the commercial software Comsol multiphysics®, is used to calculate the evolution of dislocation density during the ingot solidification and cooling. Thermo-elastic stress, due to temperature field inside the ingot during elaboration, is linked to the evolution of the dislocation density by the Alexander and Haasen model (A&H model). The purpose of this study is to show relevance of commercial software to predict dislocation density in ingots.
In a first, A&H physical model is introduced for a 2D axisymmetric geometry. After a short introduction, modification of Comsol software is presented in order to include A&H equations. This numerical model calculates dislocation density and plastic stress continuously during solidification and cooling of ingot. Results of this model are then compared to dedicated home-made simulation software. Results are also compared to characterization of a silicon ingot elaborated in a gradient freeze furnace. Both of this comparison shows the relevance of using a commercial code, as Comsol, to predict dislocations multiplication in a silicon ingot during elaboration.
Atomic scale design of epitaxial interfaces: clusters, stripes and nanowires
Michail Michailov and Bogdan Ranguelov
Institute of Physical Chemistry, Bulgarian Academy of Sciences, Sofia 1113 Bulgaria
email: [email protected]
The present lecture outlines an important area in the application of computer modelling to crystal growth, surface and interface phenomena. Being relevant to the fundamental physical problem of competing atomic interactions in systems with reduced dimensionality, these phenomena attract special academic attention. On the other hand, detailed knowledge of the fine atomic structure of interfaces is essential for understanding and solving a large number of practical problems in contemporary material science. Typical examples are formation of nanoscale surface patterns, two-dimensional superlattices, atomic intermixing at epitaxial interface, transport phenomena of atoms and atomic clusters, structure and stability of quantum wires on surfaces. In the present report we discuss a variety of diffusion mechanisms that control nanoscale interface patterning by surface-confined atomic exchange, formation of alloyed atomic stripes and islands, relaxation of pure and alloyed atomic terraces, migration of clusters and their stability in external field. The computational Monte Carlo model refines important details of diffusion of adatoms and clusters accounting for the energy barriers at specific atomic sites: smooth domains, terraces, steps and kinks. This systematization imply classification order of surface alloying: blocked, incomplete, and complete. The diffusion kinetics, integrity and decomposition of atomic islands in an external field are considered in detail and assigned to specific energy regions depending on the cluster stability in mass transport processes. Step roughening impact on atomic step permeability phenomena is discussed. The presented ensemble of diffusion scenarios opens a way for nanoscale surface design towards regular atomic interface patterns with exotic physical features. Finally, the lecture discusses the problem of thermal stability of metal nanowires on crystal surfaces. The spontaneous breakdown of free-standing or interface-located monatomic nanowires is considered in a model involving consecutive three-step mechanism for nanowire rupture, grounded on formation of active atoms, atomic vacancies and vacancy clusters. The present report also demonstrates the extended capability of atomistic models in computer simulations to unravel simultaneously acting effects, to distinguish between them, and finally to evaluate their specific contribution to experimentally observed complex physical phenomena.
References: [1] M. Michailov “Classification Order of Surface-Confined Intermixing at Epitaxial Interface” in: “Nanophenomena at Surfaces: Fundamentals of Exotic Condensed Matter Properties”, Springer Series in Surface Science 47, Chapter 6, p. 145-168, M. Michailov (Ed), Springer, Berlin Heidelberg 2011 [2] M. Michailov “Computational Study of Stripe Alloy Formation on Stepped Surfaces” Phys. Rev. B, 80, p. 035425 (2009) [3] M. Michailov, M. Vladkov “Surface Diffusion of Pb Clusters on Cu(111) Influenced by Size Dependent Cluster- Substrate Misfit: Monte Carlo Tight Binding Simulation Model” Surface Science 601, 18, p.3912 (2007) [4] B. Ranguelov and M. Michailov “Atomic diffusion on vicinal surfaces: step roughening impact on step permeability” Journal of Phys. CS 558 (2014) 012004 [5] M. Michailov, D. Kashchiev “Monatomic metal nanowires: “Rupture kinetics and mean lifetime”, Physica E 70 (2015) p.21–27
Numerical analysis of dislocation density in multicrystalline silicon for solar cells using experimental verification
Satoshi Nakano1, Bing Gao1, Karolin Jiptner2, Hirofumi Harada2, Yoshiji Miyamura2, Takashi Sekiguchi2, Masayuki Fukuzawa3and Koichi Kakimoto1
1Research Institute for Applied Mechanics, Kyushu Univ., 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580 (Japan) 2NIMS, 1-1 Namiki, Tsukuba, Ibaraki, 305-0044 (Japan) 3Kyoto Institute of Technology, Matsugasaki, Kyoto, 606-8585 (Japan) *email: [email protected]
In recent days, monocrystalline silicon is mainly produced by the Czochralski method. This method can produce high-quality and dislocation-free silicon ingot, but production cost is high. The directional solidification technique can produce multicrystalline silicon ingot for solar cells and reduce the production cost. However dislocations in multicrystalline silicon have been identified as one of the most problem for improving the efficiency of solar cells [1]. Therefore, it is necessary for the demand of increasing the efficiency of solar cells to reduce the dislocation density. Experimental measurement is an important method for evaluating the quality of silicon for solar cells [2], but it is very difficult to clarify how to multiply dislocation density during growth and cooling process. Moreover, it is also difficult to investigate how to reduce the dislocation density. Therefore, numerical simulation is an important tool for having these knowledge. We developed the three-dimensional Alexander–Haasen model to investigate distribution of dislocation density in the crystal [3, 4]. Figure 1 shows the ditribution of disloaction density at center line as a function of the height from the bottom of the crystal. The results show that the Figure 1. Disloaction density at center line dislocation density in the crystal for calculation as a function of the height from the bottom data is close to that for experimental data. of the crystal Therefore, we can predict the dislocation density more quantitavely by using our method.
Acknowledgement This work was partly supported by the New Energy and Industrial Technology Development Organization (NEDO) under the Ministry of Economy, Trade and Industry (METI).
References: [1] K. Arafune, T. Sasaki, F. Wakabayashi, Y. Terada, Y. Ohshita, M. Yamaguchi, Physica B 376-377 (2006) 236. [2] K. Jiptner, M. Fukuzawa,Y.Miyamura, H.Harada, T.Sekiguchi, Jpn. J. Appl. Phys. 52 (2013) (065501-1). [3] B. Gao, S. Nakano, H. Harada, Y. Miyamura, K. Kakimoto, Cryst. Growth Des 13 (2013) 2661. [4] B. Gao, K. Jiptner, S. Nakano, H. Harada, Y. Miyamura, T.Sekiguchi, K. Kakimoto, J. Cryst. Growth, 411 (2015) 49.
Numerical Modeling of Titanium Distribution in Sapphire Crystals Grown by the Kyropoulos Method
Carmen Stelian*1, Gourav Sen1, Nicolas Barthalay2, Thierry Duffar1
1SIMAP-EPM, 1340 Rue de la Piscine, BP 75, F-38402 Saint Martin d’Hères (France) 2Le Rubis SA, BP 16, 38560 Jarrie Grenoble (France) *email: [email protected]
Sapphire crystals grown by using the Kyropoulos method excel the competition in structural quality, size and production costs. Ti-doped sapphire crystals are of large interest as active media for the future high power laser chains. Large size Ti-doped sapphire crystals have been successfully grown by Le Rubis SA Company. The optical characterization of 10 cm diameter crystals has shown a non-uniform radial distribution of titanium [1]. The analysis of Ti3+ ion radial distribution in several slices of 1 cm thickness, have shown that the concentration is higher at the periphery of the crystal as compared to the central part of the ingot, which has a nearly uniform composition. In the present work, a transient model has been developed in order to simulate the heat, momentum and species transport during the growth of Ti-doped sapphire crystals by Kyropoulos method. The modeling is performed in two steps. First, a global model is used to simulate the heat exchanges in the whole furnace. Then, the temperature distribution carried out from the global simulation is used as thermal boundary condition for modeling the solidification process in an axi-symmetric domain containing the sample and the crucible. The transient computations show an unsteady flow generated by the strong interaction between the convection and the thermal field. The flow pattern, which is changing periodically in time, is characterized by two main flow cells. The first one is located near the symmetry axis, with the fluid moving down to the bottom of the crucible. The second vortex has a lower intensity and is located near the free surface of the melt. The shape of the isotherms is strongly affected by the buoyancy convection. The intense flow occurring at the symmetry axis influences the crystal-melt interface, which becomes conically shaped a short time after starting the growth process. Computations of Ti distribution show a uniform composition of the melt due to the intense convective mixing. The non-uniform radial profile measured in the grown ingot is explained by the conical shape of the crystal-melt interface. The lateral part of the sample is solidified at a later stage of the growth process, as compared to the central part. At that time, the concentration of titanium in the liquid increases, due to the chemical segregation at the growth interface. That explains the radial U-shaped profile with higher Ti concentration at the crystal periphery.
References: [1] Nehari A., Brenier A., Panzer G., Lebbou K., Godfroy J., Labor S., Legal H., Cheriaux G., Chambaret J.P., Duffar T., Moncorge R., Cryst. Growth Des. 11 (2011) 445.
Evolution of grains during solidification of silicon – attempts of numerical simulations for an understanding
Miller Wolfram*1, Popescu Alexandra2
1Leibniz Institute for Crystal Growth (IKZ), Max-Born-Str. 2, 12489 Berlin (Germany) 2Faculty of Physics, West University of Timisoara, Bd. v. Parvan 4, 300223 Timisoara
*email: [email protected]
Despite the great importance of direct solidification of silicon for application in photovoltaics there is still a lack of detailed understanding of the evolution of grains, grain boundaries and dislocations. Different attempts have been made to tackle the problem by numerical simulations. We present calculations on the mesoscopic level by means of a phase field method. The influence of growth parameters as cooling rate and temperature gradient will be discussed for particular examples. This includes some remarks on the growth kinetics of {111} facets and interfacial energies between melt and crystal as well as between grains of different orientations. In the mesoscopic calculations we mimic the typical process by a fixed temperature at the boundary of the melt, decreasing in time by a given cooling rate [1]. On the boundary of the solid we apply a heat flux removing the incoming heat by the initial temperature gradient in the melt and the heat produced by solidification defined by the initial temperature gradient and he given cooling rate.
These mesoscopic calculations will be set into the context with macroscopic computations and an outlook will be given.
References: [1] W. Miller, A. Popescu, C. Cantù, J. Crystal Growth, 385 (2014) 127
Analytic scaling function for size distributions of 2D surface islands V. G. Dubrovskii1-3, N. V. Sibirev1, Yu. S. Berdnikov1 1St. Petersburg Academic University, Khlopina 8/3, 194021, St. Petersburg, Russia 2Ioffe Physical technical Institute RAS, Politekhnicheskaya 26, 194021, St. Petersburg, Russia 3ITMO University, Kronverkskiy pr. 49, 197101 St. Petersburg, Russia
Modeling of island size distributions (ISDs) is paramount both in terms of pure understanding of physical properties of irreversible systems and of progress toward tailoring the island morphology. One of the most interesting features of the ISDs is the scaling property suggesting that, in the limit of high ratios of the adatom diffusion constant over the deposition rate, the ISD scales as n(x, s ,) [ / s 2 ] f (x) . Here, s and are the time-dependent mean size and coverage, respectively, and f (x) is a universal scaling function of the scaled size s / s . We obtain an explicit solution for the island size distribution described by the rate equations for irreversible p growth with the capture rates s () (a s 1) for all sizes s 1. Our solution has the form [1]
(a p) f (x) ( p 1)b p1 x p (bx,a p), (a 1) withb (a 1)( p 1) /( p 2) , as the gamma-function and as the regularized incomplete gamma- function [Fig. 1 (a)]. This function depends on the two parameters a and p, is monotonically decreasing at p 0 , monomodal at p 0 and is capable of describing a rich variety of distribution shapes [Fig. 1 (b)].
(a) (b) Fig. 1. (a) Collapse of the numerical solutions at a 2 , p 0.5 and different times (symbols) to the analytic scaling function (line); (b) Scaling function at p 1/ 2 and different a .
The obtained results suggest that the scaling features of the ISDs are closely related to the size-linearity of the capture rates. A simple analytic scaling is obtained here rigorously and helps to gain a better theoretical understanding of possible origins of the scaling behavior. We also consider how our results fit the experimental size distributions of Ga, In, Al and Mn linear atomic chains on Si(100)-2×1 surfaces [2]. References [1] V.G. Dubrovskii and N.V. Sibirev, Phys. Rev. E 91 (2015) 042408. [2] V.G. Dubrovskii and Yu.S. Berdnikov, J. Chem. Phys. 142 (2015) 124110.
On Modeling Interface Attachment Kinetics in Melt and Solution Growth Systems
Oleg Weinstein1, Oren Bass1, Alexander Virozub1, Andrew Yeckel2, Wolfram Miller3, Jeffrey J. Derby2, Simon Brandon*1
1Dept. of Chemical Engineering, Technion, Haifa (Israel) 2Dept. of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN (USA) 3Simulation & Characterization, Leibniz Institute for Crystal Growth, Berlin (Germany) * [email protected]
Interface attachment kinetics obviously always takes place at fluid/crystal interfaces during crystal growth from a fluid phase. However, when modeling crystal growth processes it is not always necessary to explicitly account for this phenomenon. In such situations the departure from equilibrium at the growing interface can be neglected and its shape and position can be tracked based on the analysis of transport phenomena and, when relevant, capillarity. This is often the case in many melt growth systems in which the melt/crystal interface position typically coincides with the melting-point temperature of the growing crystal. At the same time, certain melt growth systems and most large-scale solution growth processes do exhibit evidence of the importance of interface attachment kinetics in determining growth characteristics. This evidence is typically provided in the form of faceting along the evolving fluid/crystal interfaces. Such facets are indicative of relatively slow kinetics (in particular crystallographic orientations) requiring a significant departure from equilibrium to sustain growth. Modeling growth of such systems requires the combined analysis of transport phenomena, interface attachment kinetics and (when necessary) capillarity. The strong anisotropy in growth kinetics, the related combined action of different growth mechanisms, and the significant difference in time scales associated with relevant phenomena, make it particularly challenging to model such systems. In this contribution we will review our methods for modeling interface attachment kinetics in melt and solution growth systems and show sample calculations with specific reference to a number of important questions. These include the physics occurring at junctions between different surfaces in melt-growth systems, the dynamics associated with sudden changes in growth mechanisms, the interaction between anisotropic capillarity along the triple phase line and anisotropy (i.e. faceting) due to attachment kinetics along the melt/crystal interface in Czochralski growth systems, the physics of step sources and sinks at edges joining faces in solution growth systems and issues related to differences in time scales associated with interface attachment kinetics and transport phenomena.
Tailoring crystal growth more and more quantitatively via multiscale simulations
Prof. Dr.-Ing. Heike Emmerich1
1University Bayreuth, Universitätsstraße 30, 95440 Bayreuth (Germany) email: [email protected]
Due to the global market situation, the world wide materials industries experiences a strong pressure to develop advanced materials with special purpose properties at successively decreasing time scales. Thus there is a steadily growing importance of systematic materials development supported by computer simulation methods. Indeed, materials science simulation methods have matured to this point: There has been a growing impact on materials development by modeling and simulation at all relevant length scales (quantum-mechanical, atomic, mesoscopic, continuum). Dedicated methods have been designed for each length scale, as well as methods to address scale- bridging phenomena (multi-scale modeling).
The talk gives an overview how these methods can contribute more and more quantitatively to main features of bulk as well as epitaxial growth with a strong focus on nucleation and successive microstructure evolution and what kind of insight is possible at what kind of computational price.
The methodological focus is on a synergetic combination of DFT, KMC, phase-field crystal and phase-field methods as well as efficient experimental calibration and comparison. Precise scenario, insight-gained tied to necessary model and simulation advances are depicted for Si as well as AlN growth.
Phase field simulations of particle capture during directional solidification of silicon for solar cells Emmerich Heike Emmerich1, Hörstermann Henning Hörstermann*1, Kundin Julia Kundin1, Friedrich Jochen Friedrich2, Azizi Maral Azizi2, Reimann Christian Reimann2, Cröll Arne Cröll3, Jauß Thomas Jauß3, Sorgenfrei Tina Sorgenfrei3
1University of Bayreuth, Chair of Material and Process Simulations, Bayreuth (Germany) 2Fraunhofer IISB, Erlangen (Germany) 3University of Freiburg, Institute for Geosciences, Freiburg (Germany) *email: [email protected]
We study the interaction between the solidification front and the SiC particles present in the melt during the growth process of silicon for solar cells. These and other particles can form in the melt as a result of contamination. Usually, particles of a given size are pushed in front of the solidification front for growth velocities below a critical value and are incorporated into the crystal for growth velocities exceeding this value. During the growth of silicon crystals for solar cells, process parameters should be selected in a way that most of the particles are pushed as captured particles reduce the efficiency of the solar cell. In order to describe the relationship between critical particle size and critical growth velocity, existing theoretical models for particle capture usually assume an equilibrium of all forces acting on the particle while moving with the same velocity as the solidification front (see e.g. [1] and references therein). For silicon carbide particle in silicon, these models predict significantly higher critical particle sizes than observed in experiments [2]. Furthermore, experiments suggest that the relation between critical growth velocity and particle size can not be described by a power law [3], as most of the theoretical models predict. In addition to adapting existing theories [4,5] in order to explain these deviations, we use a phase-field model to systematically study the influence of different choices for the repulsive interactions between particle and solidification front, partial engulfment of the particle by the solidification front, non-spherical particle shapes, and different capture scenarios on the predicted critical particle size and its dependence on the growth velocity [6]. We find that the critical particle size is often substantially dependent on the shape and surface roughness of the particles: the mass of the critical particle, for example, can change by a factor of five if the particle's aspect ratio changes by merely 3%. In comparison, the predictions from models that use different repulsive forces and capture scenarios but predict the same critical particle size at one growth velocity, for its value at a growth velocity twice as high typically differ by less than 10%. We assess the implications of these results on the typical approach to compare the predictions for critical growth velocities for particles of different size with experimental results in order to test the validity of a theoretical model. We propose how a better differentiation between models can be achieved.
References: [1] R. Asthana and S. Tewari, Journal of materials science, 28 (1993) pp. 5414–5425 [2] A. K. Søiland, Silicon for solar cells, PhD thesis, NTNU, 2004. [3] J.J. Derby, Oral presentation, CSSC-8, Bamberg, May 5-8, 2015 [4] A.V. Catalina, S. Mukherjee, D.M. Stefanescu, Metall. Mater. Trans. A 31 (2000) pp. 2559–2568, 2000 [5] J. Kundin et al., in preparation [6] H. Hörstermann et al., in preparation
Phase-field study of morphological evolution during directional solidification: influence of temperature gradient and convection
Ankit, Kumar*1,2, Selzer, Michael1,2, Bhattacharya, Avisor1,2, Nestler, Britta1,2
1Institute of Applied Materials (IAM), Karlsruhe Institute of Technology, Haid-und-Neu Str. 7, 76131 Karlsruhe (Germany) 2Institute of Materials and Processes (IMP), Karlsruhe University of Applied Sciences, Moltkestr. 30, 76133 Karlsruhe (Germany) *email: [email protected]
In the past, phase-field method has been applied to address various aspects of topological evolution accompanying solidification [1,2] and precipitation [3,4,5]. Particularly the solidification of alloys is known to yield patterns of great geometrical complexity, such as dendrites, cells, or faceted morphologies. In the present work, we employ the multiphase-field model [1] to study the influence of applied temperature gradient on the polycrystalline evolution (Fig. 1a) in binary alloys. Using faceted anisotropic interfacial energy and kinetic functions, the numerical simulations are carried in the parameter space of practical interest and compared with experimental findings. Next, we discuss the influence of convective fluid on the morphological evolution and growth competition due to the misorientation (w.r.t most-preferred-orientation) amongst neighboring crystals. In the arena of dendritic solidification, it is well known that the fluid flow modifies the convective heat transport away from the dendrite tip. In absence of convective flow, a small perturbation of the preexisting solid layer evolves as instability. As a result of strong solute segregation adjacent to the primary arm, new instabilities, similar to damped wave patterns, evolve as shown in Fig. 2c. Repeated nucleation adjacent to primary instability is also seen for the case of needle-like growth in diffusion-controlled regime (Fig. 2b). Finally, it is shown that the imposed fluid flow curtails the nucleation of such new instabilities as the primary arm evolves (Fig. 2d).
Figure 1. Phase-field simulation of directional (a) polycrystalline (b) needle-like and (c) dendritic growth. (d) Same as (c) with imposed fluid flow.
References: [1] Nestler B., Garcke H., Stinner B., Phys. Rev. E, 71(2005) 041609. [2] Selzer M., Jainta M., Nestler B., Phys. Status Solidi B, 246(2009) 1197-1205. [3] Ankit K., Nestler B., Selzer M., Reichardt M., Contrib. Mineral. Petrol., 166(2013) 1709-1723. [4] Ankit K., Urai J., Nestler B., J. Geophys. Res.-Sol. Ea. (2015) doi: 10.1002/2015JB011934. [5] Ankit K., Selzer M., Hilgers C., Nestler B., J. Petrol. Sc. Res., (2015) in press.
Phase-Field Crystal Modeling of Heterogeneous Nucleation and Heteroepitaxy
László Gránásy1,2,*, Frigyes Podmaniczky1, Gyula I. Tóth1,3,György Tegze1, Tamás Pusztai1
1Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, POB 49, Budapest (Hungary) 2Brunel Centre for Advanced Solidification Technology, Brunel University, Middlesex UB8 3PH, Uxbridge (U.K.) 3Department of Physics and Technology, University of Bergen, 55 Allégaten, 5007 Bergen (Norway) *email: [email protected]
Crystallization of supersaturated liquids usually starts by epitaxial growth or by heterogeneous nucleation on foreign surfaces. Herein, we review recent advances made in modeling heteroepitaxy and heterogeneous nucleation on flat/modulated surfaces and nanoparticles within the framework of a simple dynamical density functional theory, known as the Phase-Field Crystal (PFC) model [1-3]. The crystalline substrate is represented by spatially confined periodic potentials. It will be shown that the contact angle and the nucleation barrier are non-monotonous functions of the lattice mismatch between the substrate and the crystalline phase. In continuous cooling studies for substrates with lattice mismatch, we recover qualitatively the Matthews–Blakeslee mechanism of stress release via the misfit dislocations. The simulations performed for particle-induced freezing will be confronted with recent analytical results, exploring thus the validity range of the latter. It will be demonstrated that time-dependent studies are essential, as investigations based on equilibrium properties often cannot identify the preferred nucleation pathways. Results obtained with diffusive dynamics [1-3] (applicable to colloids) and with a hydrodynamic extension of the PFC theory [4] (for simple liquids) will be compared. Modeling of these phenomena is essential for designing materials on the basis of controlled nucleation and/or nano-patterning.
Figure 1. Island formation of 2D hexagonal structure of faceted crystal habit on a square-lattice substrate in the 2D PFC model for a lattice mismatch of 14%. On the right the Voronoi polyhedron map is shown: Colors grey, blue, yellow, and red stand for nearest neighbor numbers of 4, 5, 6, and 7, respectively.
References: [1] Elder K.R., Katakowski K., Haataja M., Grant M., Physical Review Letters 88 (2002), 245701. [2] Emmerich H., Löwen H., Wittkowski R., Gruhn T., Tóth G.I., Tegze G., Gránásy L., Advances in Physics 61 (2012) 665. [3] Tóth G.I., Tegze G., Pusztai T., Gránásy L., Physical Review Letters 108 (2012), 025502. [4] Tóth G.I., Gránásy L., Tegze G., Journal of Physics: Condensed Matter 26 (2014) 055001.
Phase-field Modelling of Spiraling Ternary Eutectic Dendrites László Rátkai1,*, Tamás Pusztai,1 Attila Szállás,1 László Gránásy1,2
1Institute of Solid State Physics and Optics, Wigner Research Centre for Physics, POB 49, Budapest (Hungary) 2Brunel Centre for Advanced Solidification Technology, Brunel University, Middlesex UB8 3PH, Uxbridge (U.K.) *email: [email protected] Extending previous work [1], we have studied the formation of eutectic dendrites in a model ternary system within the framework of the phase-field theory. We have mapped out the domain in which two-phase dendritic structures grow. With increasing pulling velocity, the following sequence of growth morphologies is observed: flat front lamellae eutectic colonies eutectic dendrites dendrites with target pattern partitionless dendrites partitionless flat front (Figure 1). We confirm that the two-phase and one-phase dendrites have similar forms, and display a similar scaling of the dendrite tip radius with the interface free energy. It is also found that the possible eutectic patterns include the target pattern, and single- and multi-arm spirals, of which the thermal fluctuations choose. The most probable number of spiral arms increases with increasing tip radius and with decreasing kinetic anisotropy. Our numerical simulations confirm that in agreement with the assumptions of a recent analysis of two-phase dendrites [2], the Jackson-Hunt scaling of the eutectic wavelength with pulling velocity is obeyed in the parameter domain explored, and that the natural eutectic wavelength is proportional to the tip radius of the two-phase dendrites. Finally, we find that it is very difficult/virtually impossible to form spiraling two-phase dendrites without anisotropy, an observation that seems to contradict the expectations outlined in Ref. [2]. Yet, it cannot be excluded, that in isotropic systems two-phase dendrites are rare events difficult to observe in simulations.
Figure 1. Solidification morphology and pattern formation as a function of dimensionless pulling velocity. The c1 and c2- rich solid solutions are coloured red and yellow, respectively, whereas the liquid is transparent, and purple stands for c1
c2. The front view (top row), the longitudinal section (central row) and transverse cross sections (bottom row) are displayed. References: [1] Pusztai T., Rátkai L., Szállás A., Gránásy L., Phys. Rev. E 87 (2013) 032402. [2] Akamatsu S., Bottin-Rousseau S., Faivre G., Brener E.A., Phys. Rev. Lett. 112 (2014) 105502.
Time Evolution of 2D Cellular Automata with “Crystal Growth” Rules
Alexander Kolevski1, Hristina Popova2, Georgi As. Georgiev3, Vesselin Tonchev2
1Alexandrovska University Hospital, 1 Georgi Sofijski str., Sofia (Bulgaria) 2Institute of Physical Chemistry, Bulgarian Academy of Sciences, 11 Acad. Georgi Bonchev str., Sofia (Bulgaria) 3Faculty of Biology, University of Sofia “St. Kliment Ohridski”, 8 Dragan Tsankov blvd.. Sofia (Bulgaria) *email: [email protected]
With crystal growth (CG) in complex environments in mind (protein crystallization, bio-film drying patterns) we build a set of 2D Cellular Automata (CA) with each cell having three possible states: 0, 1(single atom) and 2 (crystalline). The state of a cell in time t=i+1 is determined by the states of five cells in t=i (the cell itself and its nearest neighbors). The number of rules for these CA is 3^(3^5), thus the common notions of CG are used for rule selection. The general (batch crystallization) setup of our simulations is: define the rule - how 1-cell transforms in 2-cell; create a random subset of 1-cells, others are 0 with no further addition of 1-cells; update the cells using the rule; attempt exchanging the values of all 1-cells with a neighbor in state 0; repeat until all 1-cells “crystallize” (turn in 2-cells). One “hopping” and one “growth” update (see [1]) form one time step, thus permitting to monitor the evolution of the number of 2-cells. We start with the simplest rule – every time a cell in state 1 has a neighbor in state 1 or 2 it also turns in state 2 (critical nucleus of two atoms). The time evolution is of Kolmogorov-Avrami (KA) type [2], the parameters change with the initial number of 1-cells. Increasing the number of necessary non-zero neighbors changes the range of parameter values in the KA equation. Next we study DLA CA populating the lattice with 1-cells and placing a 2-cell in the center while forbidding further nucleation (Figure 1a, in green). In one subset of the simulations we add unidirectional bias – hops in right are with higher probability (Figure 1a, in red) than those in left. Bias changes the canonical fractal dimension of 1.71, thus caution is needed when measuring fractal dimensions in such cases. Time evolution of the crystalline phase is of logistic type but it has a universal form (Figure 1b, inset). We conclude with even more complex automata to account for the existence of more nuclei (double impulse technique). Authors acknowledge the financial support from grant T02-8/121214. VT is grateful to Christo Nanev and Isak Avramov for the numerous discussions.
Figure 1. Cellular Automaton with “DLA” rule (pbc hold), initial occupation 10%: (a) bias modifies the fractal dimension of 1.71 in a complex manner; (b) time evolution is also affected, both dependencies are collapsed onto an universal logistic curve one with K=6.3 (inset).
References: [1] D’Souza R., Margolus N., Physical Review E, 60 (1999) 264. [2] Avramov I., Physica A, 379 (2007) 615.
POSTER
S02-P01 Atomic scale design of epitaxial interfaces: clusters, stripes and nanowires
Michail Michailov and Bogdan Ranguelov
Institute of Physical Chemistry, Bulgarian Academy of Sciences, Sofia 1113 Bulgaria
email: [email protected]
The present lecture outlines an important area in the application of computer modelling to crystal growth, surface and interface phenomena. Being relevant to the fundamental physical problem of competing atomic interactions in systems with reduced dimensionality, these phenomena attract special academic attention. On the other hand, detailed knowledge of the fine atomic structure of interfaces is essential for understanding and solving a large number of practical problems in contemporary material science. Typical examples are formation of nanoscale surface patterns, two-dimensional superlattices, atomic intermixing at epitaxial interface, transport phenomena of atoms and atomic clusters, structure and stability of quantum wires on surfaces. In the present report we discuss a variety of diffusion mechanisms that control nanoscale interface patterning by surface-confined atomic exchange, formation of alloyed atomic stripes and islands, relaxation of pure and alloyed atomic terraces, migration of clusters and their stability in external field. The computational Monte Carlo model refines important details of diffusion of adatoms and clusters accounting for the energy barriers at specific atomic sites: smooth domains, terraces, steps and kinks. This systematization imply classification order of surface alloying: blocked, incomplete, and complete. The diffusion kinetics, integrity and decomposition of atomic islands in an external field are considered in detail and assigned to specific energy regions depending on the cluster stability in mass transport processes. Step roughening impact on atomic step permeability phenomena is discussed. The presented ensemble of diffusion scenarios opens a way for nanoscale surface design towards regular atomic interface patterns with exotic physical features. Finally, the lecture discusses the problem of thermal stability of metal nanowires on crystal surfaces. The spontaneous breakdown of free-standing or interface-located monatomic nanowires is considered in a model involving consecutive three-step mechanism for nanowire rupture, grounded on formation of active atoms, atomic vacancies and vacancy clusters. The present report also demonstrates the extended capability of atomistic models in computer simulations to unravel simultaneously acting effects, to distinguish between them, and finally to evaluate their specific contribution to experimentally observed complex physical phenomena.
References: [1] M. Michailov “Classification Order of Surface-Confined Intermixing at Epitaxial Interface” in: “Nanophenomena at Surfaces: Fundamentals of Exotic Condensed Matter Properties”, Springer Series in Surface Science 47, Chapter 6, p. 145-168, M. Michailov (Ed), Springer, Berlin Heidelberg 2011 [2] M. Michailov “Computational Study of Stripe Alloy Formation on Stepped Surfaces” Phys. Rev. B, 80, p. 035425 (2009) [3] M. Michailov, M. Vladkov “Surface Diffusion of Pb Clusters on Cu(111) Influenced by Size Dependent Cluster- Substrate Misfit: Monte Carlo Tight Binding Simulation Model” Surface Science 601, 18, p.3912 (2007) [4] B. Ranguelov and M. Michailov “Atomic diffusion on vicinal surfaces: step roughening impact on step permeability” Journal of Phys. CS 558 (2014) 012004 [5] M. Michailov, D. Kashchiev “Monatomic metal nanowires: “Rupture kinetics and mean lifetime”, Physica E 70 (2015) p.21–27
S02-P02 A single-domain approach to simulate the effect of convective flow on the mushy zone structure in Czochralski growth of semitransparent oxide crystal Reza Faiez*, Majid Mashhoudi, Yazdan Rezaei
1 Solid State Lasers Department, Laser & Optics Research School, Tehran P.O. Box 11365-8486, Iran *email: [email protected]
In the growth model considered, the two-dimensional convective flow in GGG melt (Pr=4.69) is
3 2 characterized by Ra=5.353×10 ΔTmax , Ma=2.742×10 ΔTmax, and Re=127.12Ω (rad/s) where 0.5
≤Ω (rad/s)≤3.0 is the crystal (rx = 30mm) rotation rate and the applied ∆Tmax=67K ensures the growth at the tri-junction point. Both the crystal and melt have the same optical properties (n=1.8, a=258 m-1) and discrete ordinates method was used to estimate the radiative heat flux in the equation of energy. The phase field method was used to solve the phase change problem with convetion. This method is based on a single-domain approach where a system of momentum and energy equation is solved in the entire physical domain. For the cases with Ω≤2.0, the fluid motion within the mushy zone is dominated by the buoyancy and thermocapillary forces ( Ur<0). The radial velocity sign was changed when the rotation rate slightly increased to Ω=2.3. This can be infered that, in the cases with Ω≥2.3 the rotationally driven convection plays a predominant role inside the mushy region. As well, the ratio between the vertical and horizontal temprature gradient beneath the zone, gz/gr found to be decreased to the values smaller than unity for the cases with Ω≥2.3, at which the shape of mushy region was largely modified. This abrupt deformation of the mushy zone found to be correlated with a baroclinic instability in the fluid resulting in cold plumes detaching from the crystal and desending towards the crucible bottom. It was shown that, increasing Ω, the gradiant Richardson number, Rig increases and the thermal Rossby number, RoT decreases. The linear analysis predicts the onset of geostrophic instability when Bu≤0.58. This condition was satisfied for Ω≥2.3. Remarkably, in this model, the Burgers number is very close to its critical value (Bu*=0.58), when Ω=2.3 as shown in figure 1.
2 Figure 1. The dimensionless parametes, Rig, Bu, RoT and Gr/Re each as a function of the 2 32 22 rotationally-driven flow intensity, Rerx / where Gr glc Tmax r / , Rigr N/( u / z ) , 2 22 2 Bu[( N /2 )( hcc / r )] , RoTl g (/)/( T z h c r cx r ) and N is the buoyancy frequency.
S02-P03 Modeling of patterns by the phase field crystal method in three dimensions
Ilya Starodumov*1, Jesus Bueno2, Hector Gomez2, Peter Galenko3, Dmitri Alexandrov1
1 Laboratory of Multi-Scale Mathematical Modelling. Department of Mathematical Physics. Ural Federal University, 620000, Ekaterinburg (Russian Federation) 2 Department of Mathematical Methods. University of A Coruña. Campus de Elviña, 15192, A Coruña (Spain) 3 Friedrich-Schiller-Universität Jena, Physikalisch-Astronomische Fakultät, D-07737 Jena (Germany)
*email: [email protected]
The phase-field crystal model (PFC model) is a continuum model which describes processes on atomic length scales and patterns on the nano- and micro-length scales [1,2]. This model is characterized by a conserved field which is related to the local atomic number density, such that it is spatially periodic in the solid phase and constant in the liquid phase. The PFC model provides an efficient tool for simulating the ordering of nanoscale structures on micron length scales, liquid- solid transitions, dislocation motion and plasticity, glass formation and foams, epitaxial growth, grain boundary premelting, crack propagation, surface reconstructions, grain boundary energies, dynamics of colloidal systems, and polymers [3]. In this study, we consider the solidification of a metastable and unstable liquid state as described by the three-dimensional PFC model. The phase transition from the metastable state to the stable one occurs by overcoming the energy barrier which is usually necessary for the emergence of a new phase. Contrary to that, a transition from the unstable state proceeds without energy barrier that is usually evolves by fluctuation mechanism. Both of these transitions are modeled numerically for obtaining various crystalline patterns emerging from the liquid. For the numerical solution of the PFC model presented in Ref. [4], we have obtained a scheme based on isogeometric analysis (IGA) which allows us to generate the -continuous functions required for the numerical discretization. For integration in time, the developed numerical algorithm uses the generalized- method. The algorithm has been realized in C-language code. We have used the wide spread frameworks PetIGA and PETSc which implement NURBS-based Galerkin finite element method. Using PETSc tools has allowed us to customize code in effective parallelization mode. We have tested our program on more than 200 CPU cores as well as 10 GPU cores and in all cases we have observed productivity of calculation proportional to the increase of the number of cores. Using the developed program code, various crystal patterns in three spatial dimensions were obtained. The structure diagram has been created in coordinates “driving force-average atomic density” and compared with the diagram theoretically calculated in Ref. [5]. The developed program code can be applied for the problem of selection of the lattice parameter at the front of the periodic new phase invading homogeneous liquid or other periodic crystal lattice. The theory and program code were developed for small and large driving force of liquid-solid or solid-state transformations.
References: [1] K.R. Elder and M. Grant, Phys. Rev. E 70, 051605 (2004). [2] K.R. Elder, N. Provatas, J. Berry, P. Stefanovic, and M. Grant, Phys. Rev. B 75, 064107 (2007). [3] H. Emmerich, H. Löwen, R. Wittkowski, T. Gruhn, G. I. Toth, G. Tegze, L. Granasy, Advances in Physics 61, 665 (2012). [4] P.K. Galenko, H. Gomez, N.V. Kropotin, K.R. Elder, Phys. Rev. E 88, 013310 (2013). [5] A. Jaatinen, T. Ala-Nissila, Journal of Physics: Condensed Matter 22(20), 205402 (2010).
S02-P04 Kinetic Monte Carlo simulations of vicinal GaN(000-1) surface evolution during N-rich growth Filip Krzyżewski*1, Magdalena A. Załuska-Kotur*1 1Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, Warsaw (Poland) We use 2-component kinetic Monte Carlo model to study vicinal GaN(000-1) surface patterns. The model was recently used in the analysis of wurtzite crystals surface evolution [1]. In this work we apply it to the gallium nitride N face. Hence we improved the previous model [2-5], which was limited due to the control of only one kind of atoms forming GaN crystals. New model allows for the full control on fluxes and diffusion of all atoms. We study the influence of miscut angle, temperature and nitrogen supersaturation on the character of the surface structures that emerge during crystal growth. Different surface patterns were obtained. At steep surface with 4º miscut smooth surface with straight, parallel steps is observed. Decrease of miscut angle to 2º leads to surface roughening and a mixture of bunches and meanders emerges [1]. Numerical results agree with experimental plasma- assisted MBE (PAMBE) growth of GaN(000-1) [6]. PAMBE experiments, in low temperatures, show step flow growth mode [7]. In such a case speed of adatom diffusion plays an important role in the surface evolution process. When the diffusion is slow in comparison to the terrace width, time of particle wandering at the surface is long. Adatoms can easily encounter other atoms in their route to step edges. It leads to two dimensional nucleation on the surface. Islands which emerge in such a way are incorporated by the steps which move forward. Processes of island nucleation and step movement lead to the emergence of mixed bunched-meandered surface pattern. On the other hand, when the surface is steep, terraces are narrow and time of adatom wandering on the surface is shorter. Particles attach to the steps before they encounter other atoms. No 2D nucleation takes place and the system surface evolves to the smooth pattern. We show that increase of temperature or nitrogen flux reduces 2D nucleation at terraces. Hence in such conditions, at low miscut obtained surfaces are smoother. This work was supported by research grant from the National Science Centre (NCN) of Poland (Grant NCN No. 2013/11/D/ST3/02700).
Figure 1. Results of the simulation at lower miscut 2º Figure 2. Results of the simulation at higher miscut 4º References: [1] F. Krzyżewski and M. A. Załuska-Kotur J. Appl. Phys. 115, 213517 (2014) [2] M. A. Załuska-Kotur, et al, Cryst. Growth & Design 13, 1006 (2013) [3] M. A. Załuska-Kotur, F. Krzyżewski, S. Krukowski, Journal of Applied Physics, 109 (2011) 023515 [4] Ma.A. Załuska-Kotur, Fi.Krzyżewski, Journal of Applied Physics 111, 114311 (2012) [5] M. A. Załuska-Kotur, F. Krzyżewski, S. Krukowski, J. Cryst. Growth 343 (2012) 138 [6]C. Cheze, et. al. Appl. Phys. Lett. 103, 071601 (2013) [7] B. Heying, et al, J. Appl. Phys. 88, 1855 (2000)
S02-P05 Modeling of dendritic growth under earthly and reduced gravity conditions
P.K. Galenko*1, D.V. Alexandrov2, D.A. Danilov3, K. Reuther1, M. Rettenmayr1, D.M. Herlach4
1 FRIEDRICH SCHILLER UNIVERSITY, JENA (GERMANY) 2 Ural Federal University, Ekaterinburg (Russia) 3 KARLSRUHE INSTITUTE OF TECHNOLOGY, EGGENSTEIN-LEOPOLDSHAFEN (GERMANY) 4 GERMAN AEROSPACE CENTER, COLOGNE (GERMANY)
*email: [email protected]
A thermo-solutal problem of a free dendrite growing with high velocity under forced fluid flow is considered analytically. The present theoretical model is based on the Oseen approximation for the equations of fluid motion and takes into account small anisotropy of surface energy and atomic kinetics. A criterion for the stable dendritic growth is derived from the solvability condition by the method described in Refs [1,2]. This criterion generalizes the previous known results for the stable growth of a dendritic crystal. Model predictions are compared with experimental data on crystal growth kinetics in droplets processed in electromagnetic and electrostatic levitation facilities [3,4]. Developed theoretical and simulation methods are applied to crystallization of Ni-B, Cu-Zr and Ti- Al alloys under earthly and reduced gravity conditions. This work has been done under support from German Research Foundation (DFG Project RE 1261/8-2), Russian Foundation for Basic Research (RFBR Project No. 14-29-10282ofi_m) and by the DLR Space Management within contract 50WM1140.
References: [1] D.V. Alexandrov and P.K. Galenko, Phys. Rev. E 87, 062403 (2013). [2] D.V. Alexandrov and P.K. Galenko, Physics-Uspekhi 57(8), 771 (2014). [4] S. Binder, P.K. Galenko and D.M. Herlach, Phil. Mag. Lett. 93, 608 (2013). [5] S. Binder, P.K. Galenko and D.M. Herlach, Journal of Applied 115, 053511 (2014).
S02-P06 Relationship between stability of facet surfaces and incorporation of zinc-blende phase in InN during pressurized reactor MOVPE: A theoretical approach
Akira Kusaba*1, Yoshihiro Kangawa1, 2, Stanisław Krukowski3, Koichi Kakimoto1, 2
1Dept. Aeronautics and Astronautics, Kyushu University, Fukuoka 819-0395 (Japan) 2RIAM, Kyushu University, Fukuoka 816-8580 (Japan) 3UNIPRESS, ul. Sokolowska 29/37, 01-142 Warsaw (Poland) *email: [email protected]
In-rich InGaN is a promising material for bright green and red LEDs. However, the increase in In content tends to deteriorate the crystalline quality owing to the decrease in decomposition temperature or the optimum growth temperature. Pressurized-reactor (PR) MOVPE, which enables high-temperature film growth, is an efficient method for fabricating InGaN films of high crystalline quality and high In composition. In case of [000-1] (-c) growth, however, it has been reported that zinc-blende phase (ZB) whose growth islands have (1-1-1) facet incorporates into wurtzite phase (WZ) whose growth islands have (1-100) facet depending on growth conditions of PR MOVPE.[1] Our aim is the theoretical estimate of growth conditions when pure WZ phase grows. First, we calculated the surface energies of ideal surfaces on (1-100) and (1-1-1) facet plane based on the method that makes effective use of the symmetry of ZB structure.[2, 3] Then, we calculated the difference in free energies between (A) the system consisting of the reconstructed surface with adatoms and (B) the system consisting of an ideal surface and gas phase particles.[4] Here, the total energies were obtained by DFT calculations and the entropy of gas phase particles as function of T and p were obtained by quantum statistical mechanics. We regard the sum of surface energy of ideal surface and free energy of reconstructed surface based on ideal surface as surface energy of reconstructed surface. Figure 1 shows the difference in surface energies between (1-100) and (1-1-1) facet surfaces, i.e., σ(1-100)−σ(1-1-1). The growth conditions of WZ (blue hexagon) and ZB (red square)[1] are also shown in the figure. In this growth regime, WZ becomes stable in the high temperature and low In partial pressure region. Conversely, difference in surface energies between (1-100) and (1-1-1) becomes small under low temperature and high In partial pressure region. Moreover, σ(1-100) − σ(1-1- 1) drastically increases near the boundary of WZ/ZB mixture. These results suggest that the probability of ZB incorporation increases with decreasing difference in surface energies between (1-100) and (1-1-1). Now, we are investigating the surface phase diagram of InN(0001) to understand the growth process Figure 1. Difference in surface energies, along [0001] (+c). σ(1-100)−σ(1-1-1). References: [1] T. Kimura et al., Phys. Stat. Sol.C, 9 (2012) 654. [2] C. E. Dreyer et al., Phys. Rev. B, 89 (2014) 081305. [3] S. B. Zhang et al., Phys. Rev. Lett., 92 (2004) 086102. [4] Y. Kangawa et al., Surf. Sci., 493 (2001) 178.
S02-P07 Study of the early stages of Calcium Phosphate nucleation in water by means of ab Initio Molecular Dynamics
Mancardi Giulia*1, Terranova Umberto1, De Leeuw Nora2
1University College London, 20, Gordon street, London WC1H 0AJ (United Kingdom) 2Cardiff University, Park Place, Cardiff CF10 3AT, (United Kingdom) *email: [email protected]
Amorphous Calcium Phosphate (ACP) is the precursor phase of apatite crystals in bone and tooth tissues [1]. The formation of ACP is thought to proceed through a cluster-growth model [2]. The first step is the aggregation of prenucleation clusters (PNCs) [3], which are already present in body fluids before nucleation. PNCs are in fact ion-association complexes, with formula 4- [Ca(HPO4)3] , which aggregate in solution. Above the solubility limit of ACP, they take up 2- calcium ions from solution to form insoluble post-nucleation clusters with formula [Ca2(HPO4)3] that precipitate as ACP [3]. Here, we apply the umbrella sampling technique [4] to study the behaviour of PNCs in aqueous 2- solution. We have driven the system to the detachment of the (HPO4) group and its replacement by water, along the reaction coordinate of the distance between the central Ca2+ ion and one 2- phosphorous atom out of the three coordinated (HPO4) groups (black dotted line in Figure 1). Increasing systematically the targeted Ca-P equilibrium distance, we have performed a series of ab initio molecular dynamics simulations, aimed at investigating the potential of mean force for the phosphate-water exchange process. In addition, we discuss the effect of nearby Ca2+ counterions, reported experimentally [3], to the free energy barrier.
Figure 1. Prenucleation cluster
References: [1] Dey A., Bomans P.H.H., Muller F.A., Will J., Frederik P.M., de With G., Sommerdijk N.A.J.M., Nature Materials, 9 (2010), 1010-1014 [2] Onuma K., Ito A., Chem. Mater., 10 (1998), 3346-3351 [3] Habraken W.J.E.M., Tao J., Brylka L.J., Friederich H., Bertinetti L., Schenk A.S., Verch A., Dmitrovic V., Bomans P.H.H., Frederik P.M., Laven J., van der Schoot P., Aichmayer B., de With G., DeYoreo J.J., Sommerdijk N.A.J.M., Nat. Commun., 4 (2013), 1507 [4] Torrie G., Valleau J., Journal of Computational Physics, 23 (1977), 187-199
S02-P08 ON OBTAINING EQUILIBRIUM CRYSTAL SHAPE UNDER NON-STATIONARY CONDITIONS
Gershanov Vladimir*1, Skorynina Alina1,Garmashov Sergey1
1Southern Federal University, 5 Zorge, Rostov-on-Don (Russia) *email: [email protected]
The criterion for the equilibrium shape of a crystal contacting with its solution in some solvent is the equality of the equilibrium concentrations in the liquid along the solid-liquid interface. The equilibrium concentrations at all parts of the interface are determined only by the Gibbs-Thomson effect, i.e. by the capillary effects. The equilibrium crystal shape is a particular case of the inverse Gibbs-Thomson effect [1], when the mass transfer in the crystal-solution system proceeds under the action of capillary forces under negative feedback conditions. Generally, the mass transfer in the crystal-solution system takes place when both the interfacial energy and interface kinetics are anisotropic. The higher value of the interfacial energy stimulates obtaining the equilibrium shape, while interface kinetics and its anisotropy, in contrast, prevent this process and lead to one of growth shapes. Therefore, in order to obtain the equilibrium shape, it is important to eliminate the kinetic restrictions on the mass transfer at the solid-liquid interfaces. As shown in [2], this is possible under non-stationary thermal conditions only. We consider the case of the negative crystal, but, in our opinion, the result is also to be true for the case of the positive crystal. As shown in [2], the influence of interface kinetics can be eliminated at the rates of temperature changes that generate supersaturations (at cooling) and undersaturations (at heating) in the solution volume much larger than the critical supersaturations Ccr (undersaturations Cds) needed for the crystallization (dissolution) processes at the singular interfaces. Under these conditions, the mass transfer in the solution is restricted mainly by the diffusion process, and not by interface kinetics. The complete disappearance of interface restrictions in this case is accompanied by another nonlinear effect, namely, the effect of switching diffusive fluxes between the singular and non- singular parts of the solid-liquid interface [2]. Depending on the form of the temperature oscillations, this effect determines the ratio of the areas of the singular and nonsingular parts, and, therefore, it is to be minimized for obtaining the equilibrium crystal shape. This is possible if the saw-tooth temperature oscillations satisfy the following relation: ac / ah = Ccr / Cds, where ac (ah ) are the rates of cooling (heating). We have simulated numerically the mass transfer under the non-stationary thermal conditions for the case when the shape of the modeled negative crystal coincides with its equilibrium shape. It is assumed that the negative crystal is a cylindrical liquid inclusion enclosed in a positive crystal, and, therefore, the mass transfer in the liquid can be considered as two-dimensional. The simulation has been performed using a computer program [3]. It has been shown that if the above-mentioned two criteria are met, the crystal shape remains in equilibrium if it was in equilibrium in its initial state. Otherwise, if the initial shape was not in equilibrium, the crystal obtains the equilibrium shape under the influence of the non-stationary thermal conditions.
References: [1] Gershanov V.Yu., Garmashov S.I. Technical Physics, 60 (2015) 61–65. [2] Gershanov V.Yu., Garmashov S.I. Journal of Crystal Growth. 311 (2009) 2722–2730. [3] Garmashov S.I., Gershanov V.Yu., Navigator in the World of Science and Education, 13 (2011) 63.
S02-P09 Working point of the EFG process
Laurent Carroz1, 2 and Thierry Duffar*3
1 SNECMA Villaroche, Rond-point René Ravaud, 77550 Réau, France 2 RSA, 380 Rue Rn 85 BP 16, 38560 Jarrie, France 3 SIMaP-EPM, UMR 5266 CNRS, 38402 Saint Martin d’Hères, France *email: [email protected]
The Edge-defined Film-fed Growth (EFG) technique allows growing shaped crystals directly from the melt, then avoiding post machining operations that are costly and often generate defects in the crystal. Initiated by Stepanov [1,2] cited in [3] and developed by Labelle [4], this technique, considering its potential, received a great attention very early and quickly matured to industrial process. Currently the most important for the industrial crystal grower is to find the best working point of his process. In this frame, a theoretical investigation of the EFG process working point based on the meniscus height control is carried out. The link between the two control parameters, which are the pulling rate and the upper die temperature, is analytically found from the thermal equilibrium at the crystallization interface. Using the pressure equilibrium in the film and considering the viscous drag and meniscus shape, the change in the meniscus height depending on the crystal radius is analyzed. Limited to small crystal radii, an algebraic formulation of the temperature gradient at the interface is established. Some die design parameters are taken into account and their impacts on the process working point are discussed. An example of the EFG process working point curves are given in figure 1 for different radii.
Figure 1. Example of EFG working points for crystallization of sapphire rods. V is the pulling rate, RC the crystal radius and ΔT the overheating of the shaper, above the melting point.
References: [1] A. V. Stepanov, Zh. Tekh. Fiz. 29 (1959), 382. [2] A. V. Stepanov, The future of metalworking, Lenizdat, Leningrad 1963, In Russian. [3] T. Duffar, (ed.), Crystal Growth Processes based on Capillarity: Czochralski, Floating Zone, shaping and crucible techniques, J. Wiley-Blackwell, Chichester, UK, 2010. [4] H. E. Labelle, Growth of inorganic filaments, US Patent #3471266, 1969.
S02-P11 Kinetic model of cement hydration with time-dependent rates
Valentini Luca1,2*, Artioli Gilberto1,2, Ferrari Giorgio3
1Department of Geosciences, University of Padua, via Gradenigo 6, 35131 Padua (Italy) 2 CIRCe Centre, via Gradenigo 6, 35131 Padua (Italy)3 R&D Department, Mapei SpA, Via Cafiero 22, 20158 Milan (Italy) *email: [email protected]
Cement-based materials are of fundamental importance for modern society, especially for the developing countries needing to tackle the issue of poor infrastructures. At present, the low cost and broad availability of raw materials, as well as the relatively small environmental footprint per unit volume produced, make it hardly imaginable to substitute cement with any other material. On the other hand, the large demand and annual production result in significant issues related to CO2 emissions, mainly due to calcination of limestone, the primary raw material for the manufacture of Portland cement. In order to meet the need of reducing greenhouse gas emissions without hampering the worldwide availability of cement, it is fundamental to drive research towards optimizing cement production and designing more sustainable cement-based materials, hence the need of acquiring extensive knowledge about the processes that govern the chemistry of cement. Cement hydration consists of a set of reactions by which anhydrous particles dissolve into ionic species in solution that, upon reaching supersaturation with respect to a specific phase, precipitate into hydrated solids, inducing the transformation of a fluid slurry into an elastic solid with high mechanical strength. The main product of cement hydration is a poorly crystalline, nano-scale calcium-silicate hydrate (commonly referred to as C-S-H in the field of cement chemistry) having a pseudo-tobermoritic crystal structure. The precipitation of C-S-H consists of a first nucleation step, during which new interfaces are formed in the pore solution (homogeneous nucleation) or at pre- existing particle-water interfaces (heterogeneous nucleation). Nucleation is followed by the growth or aggregation of the nuclei, as more ions are withdrawn from the pore solution and attached to the surfaces of the newly formed species. In this study, a kinetic model of the nucleation and growth of C-S-H is presented. The model is based on the combination and generalization of the Johnson-Mehl-Avrami-Kolmogorov (JMAK) and “boundary nucleation and growth” (BNG) models. Both the JMAK and BNG models had been previously used to describe cement hydration kinetics by fitting calorimetric curves. The limitation of this approach stems from the fact that constant rates of nucleation and growth are assumed. However, the rate of cement dissolution-precipitation is controlled by the time-dependent composition of the solution. Moreover, calorimetry only provides a picture of the overall kinetics, without any information about the rates of dissolution-precipitation of the single phases. Here, specific functions are used to describe the time-dependent rates of nucleation and growth. The model is then used to fit the time distribution of the C-S-H mass fraction, obtained by in-situ X-ray powder diffraction. The possibility of detecting changes in nucleation mechanisms, induced by organic and inorganic additives, will be briefly discussed.
S02-P12 Crystal surface morphology as a consequence surface diffusion anisotropy
Magdalena A. Załuska-Kotur*, Filip Krzyżewski, Marcin Mińkowski
Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland *[email protected]
Formation of various geometric patterns during crystal growth is a subject of continuous interests of many researchers. It is important as an interesting example of far from equilibrium, stationary process and because of practical applications in the crystal growth technology. Temperature, surface miscut and flux of external particle are parameters that can be used to control crystal growth in the experiment. On the microscopic base rate and character of diffusion over terraces, along and across steps is very important phenomenon that determines final surface morphology. Diffusion towards and across steps depends on so called Schwoebel barrier. During crystal growth or sublimation, the height of barrier at step determines occurrence step bunching, meandering and island step and positions. A novel variational analytic approach to the collective diffusion will be presented and illustrated in various examples [1]. Highly anisotropic diffusion is obtained for complex substrate's potential energy landscape or in the presence particle-particle interactions [2,3]. We analyze particle movement in such conditions. In some situations Schwoebel barrier at upper or lower step side is expected. As a consequence during crystal growth or sublimation surface dynamics can change drastically as an answer to slight change of external conditions. Results of calculations of diffusion coefficients for particles jumping over the surface in different conditions are then applied in the kinetic Monte Carlo simulation of crystal growth process. The kMC simulations are done for two different systems: GaN(0001) and 4H SiC(0001) [4,5]. Within certain parameters steps move uniformly and stay straight during growth or sublimation processes of both simulated crystals. We show that the presence of Schwoebel barrier or strong diffusion anisotropy change this process into unstable one, being source of bunches, meanders or both patterns emerging together. Phase diagram for all observed structure was found. All surface patterns, emerging in the simulations, have their corresponding cases in the experimental results [4]. The numerical models allow to observe how they develop and to study their time evolution.
This work was supported by research grant from the National Science Centre (NCN) of Poland (Grant NCN No. 2013/11/D/ST3/02700)
References:
[1] Magdalena A. Załuska-Kotur, Appl. Surf. Sci. 304 (2014) 122. [2] M. Mińkowski, M.A. Załuska-Kotur , J. Stat. Mech. (2013) P05004 [3] M. Mińkowski, M.A. Załuska-Kotur, Phys. Rev.B 91 (2015) 075411 [4] M. A. Załuska-Kotur, Filip Krzyżewski, Stanisław Krukowski, Michał Leszczyński, Robert Czernecki , Cryst. Growth & Design 13 (2013) 1006 [5] Filip Krzyżewski and Magdalena A. Załuska–Kotur J. Appl. Phys. 115 (2014) 213517.
S02-P13 Monte Carlo simulation of island formation during GaAs(001) homoepitaxial growth
Ageev Oleg Alekseevich, Solodovnik Maxim Sergeevich, Balakirev Sergey Vyacheslavovich*, Mikhaylin Ilya Alekseevich
Institute of Nanotechnologies, Electronics, and Electronic Equipment Engineering of Southern Federal University, 2, Shevchenko St., Taganrog (Russian Federation) *email: [email protected]
We report kinetic Monte Carlo simulation of the initial stage of GaAs homoepitaxial growth on the technologically important GaAs(001)-(2×4) reconstructed surface. The crystal is modeled as a simple cubic solid-on-solid lattice. Arsenic dimer rows and missing trenches alternate across the lattice. Atoms can interact with their nearest and next nearest neighbors. We take into account the alteration of activation energy of each included diffusion process depending on the top-layer local environment of a particle. We observe that at temperature (T) of 580°C and growth rate (v) of 0.1 monolayer (ML) per second the island density (N) is saturated after deposition of 0.06 ML GaAs. The simulation yields N = 2·1012 cm-2, in agreement with experiments. Islands are preferentially formed in the trenches and favor elongation along the [11 0] direction (Fig. 1). The simulations were performed with the different growth conditions. It is known that N goes down with temperature increase and rises with growth rate increase, and our simulations confirm that. We also observe that N depends on V/III flux ratio. We find it to rise about twice with the increase of V(As2)/III flux ratio from 3 to 40 either at lower temperature of 550°C (Fig. 2) or at higher growth rate of 1 ML/S with the other conditions being equal. At lower growth rates and higher temperatures N increases slightly with V/III ratio increase too. Whereas the growth temperature decrease leads to the reduction of adatom diffusion coefficient, and the growth rate increase enhances the probability of island formation in a random site, the flux ratio increase intensifies the process of covering of Ga pairs formed in the most favorable sites. Thereby, the growth process can be controlled by altering flux ratio without significant growth rate and temperature changes which could induce defectiveness of the structure. This work was supported by the Russian Science Foundation Grant No. 15-19-10006. The results are obtained using the equipment of Common Use Center and Education and Research Center "Nanotechnologies" of Southern Federal University.
Figure 1. Island morphology in a simulation area of Figure 2. Island density as a function of V(As2)/III flux 160 Å × 200 Å after deposition of 0.06 ML GaAs at T ratio after deposition of 0.06 ML GaAs at T = 550°C = 580°C, v = 0.1 ML/s, V(As2)/III ratio = 10 (squares), T = 580°C (circles), T = 610°C (triangles); v = 0.1 ML/s
S02-P14 Mathematical modeling of the process of growing a single crystal CdTe 100 mm by the Obreimov-Shubnikov method
Marina Pavlyuk*1, Ekaterina Sukhanova2, Marina Zykova2, Vladimir Kanevsky1, Igor Avetissov2
1A.V.Shubnikov Institute of Crystallography RAS, Leninskii pr. 59, Moscow, (Russian) 2D. Mendeleev University of Chemical Technology of Russia, Miusskaya pl. 9, Moscow, (Russia) *email: [email protected]
The growth kinetics is very important from the standpoint of improving of single crystal technology and understanding of optical and structural defects formation in the crystal during the growth process. A direct study of the kinetics of CdTe crystal growth is very difficult. Since the growing crystal is well shielded, the crystallization front (FC) in the melt and its visualization is not possible. Sometimes, in practice the FC in defective single crystals can be determined by decorating using microbubbles or by X-ray microanalysis, which allows displaying the components distribution along the growth axis and ingot diameter. These data could be applied to prove the results of numerical modeling of the growth process. The task of analysis of growth kinetics of large CdTe single crystals grown by the Obreimov-Shubnikov technique was solved by the numerical simulation using ANSYS 14.5 Fluent software. The calculation was carried out in three steps. At the first step we have calculated a thermal profile of an empty shaft furnace (Figure 1a). At the second step we simulated an internal space of the furnace with a quartz ampoule and a crucible with melt inside the ampoule (1b). At the final step we calculated the melt flows in the crucible using the thermal conditions obtained at the previous steps. The enthalpy model was used for crystallization simulation. The simulation results are consistent with the growth experiment results, confirming the adequacy of the numerical model. This work was supported by the Russian Foundation for Basic Research RFBR (grant №14-02-31726 mol_а).
a) b) Figure 1. Temperature distribution: a) thermal profile in the empty shaft furnace filled by air and b) thermal profile of the inner space of the furnace with the with a quartz ampoule and a crucible with melt inside the ampoule
S02-P16 Experimentally Verified Numerical Simulation of Germanium Single Crystals Grown by the AVC-AHP Technique
Yousefi L. Pouya*, Sheikhi Aidin, Mason Jeremy K., and Balikci Ercan
Department of Mechanical Engineering, Bogazici University, 34342 Bebek, Istanbul, Turkey *email: [email protected]
The axial heat processing (AHP) [1] and axial vibrational control (AVC) [2] techniques are used to investigate the solid/liquid (s/l) interface shape and its morphological stability during the antimony-doped germanium single crystal growth from the melt. To this end, three crystals each have been grown by the AHP and AVC techniques with varying growth parameters that include the melt height, pulling velocity, amplitude of vibration, and vibrational frequency. In the AHP method, a baffle is immersed in the molten material inside a cylindrical crucible that surrounded by a fixed furnace supplying a heat flux to the system. The baffle is used to reduce the effective melt height, measured from the s/l interface to the baffle. The AVC method additionally vibrates the submerged baffle axially to mix the melt in a controlled manner. Each crystal is ground, polished and electro-etched in a H2O and Na2SO3 solution (79.2:1) [3] to visualize the interface shape. The AHP and AVC techniques have also been simulated using ANSYS Fluent software, with the simulation parameters corresponding to the experimental growth parameters. The influence of these parameters on the flow velocity map, temperature distribution in the melt, and s/l interface shape of the growing crystal is analyzed. Since the experimental flow velocity of the Sb-doped Ge single crystal is not measurable due to opacity, additional crystal growth experiments were performed to verify the simulated flow velocity. Sodium nitrate (NaNO3) single crystals were grown inside quartz glass tubes by both the AHP and AVC methods, with aluminum powder added to the transparent melt to allow for visual capture of the flow pattern.
References: [1] E. Balikci, A. Deal, and R. Abbaschian, “Antimony-doped germanium single crystals grown from the melt by the axial heat processing (AHP) technique,” J. Cryst. Growth, vol. 262, no. 1–4, pp. 581–593, 2004. [2] I. Avetissov, V. Kostikov, V. Meshkov, E. Sukhanova, M. Grishechkin, S. Belov, and A. Sadovskiy, “Modeling of axial vibrational control technique for CdTe VGF crystal growth under controlled cadmium partial pressure,” J. Cryst. Growth, vol. 385, pp. 88–94, 2014. [3] E. Balikci, A. Deal, R. Abbaschian, S. V. Bykova, V. D. Golyshev, M. a. Gonik, V. B. Tsvetovsky, M. P. Marchenko, and I. V. Frjazinov, “A study on the morphological stability of faceted interfaces in antimony-doped germanium single crystals grown by the axial heat processing method,” Cryst. Growth Des., vol. 4, no. 2, pp. 377–381, 2004.
The study is supported by TÜBİTAK, TURKEY, grant no 212M030.
S02-P17 Microscopic modelling of confined crystal growth and dissolution
Høgberget, Jørgen*1, Røyne, Anja1, Dysthe, Dag Kristian 1, Jettestuen, Espen1,2
1Department of Physics, University of Oslo, P. O. Box 1048 Blindern N-0316, Oslo (Norway) 2International Research Institute of Stavanger, Forskningsparken AS, Gaustadalléen 21, 0349 Oslo (Norway)
We extend previous solid-fluid crystal growth and dissolution models [1] to include the effect of confinement on solute systems. This is done by adding a plane surface subject to a constant pressure at a certain equilibrium height above the crystal surface. To model the repulsive interaction between the growing and the confining surface we use a Debye-Hückel type potential. When the geometry of the growing surface changes, the value of the repulsive interaction changes, and consequently also the value of the equilibrium height. This effect is known as the “force of crystallization”. As we increase the applied pressure, we observe that the growing surface is flattened, and the equilibrium concentration increases. This effect is known as “pressure solution”. With the addition of confinement to the model, the equilibrium concentration is no longer a priori known. It is therefore an important step of the model to obtain equilibrium, such that a certain level of supersaturation can be specified. We see from our results that the model reproduce analytical equilibrium thermodynamics both with and without the effect of confinement. We will present results where we have used the model to investigate the dependency of the surface roughness with supersaturation for various levels of applied pressure, as well to parameterize the linear growth rate constant. The latter is given as the slope of the curves presented in Figure 1. These results all point in the direction that the model produce a temperature dependent asymmetry between growth and dissolution.
Figure 1. Measurements of the linear growth rate (average height per time) as a function of the supersaturation for a crystal growing in confinement under various applied pressures (indicated by different lines). The supersaturation is calculated using the equilibrium concentration at the given pressure.
References: [1] Gilmer G. H. and Bennema P., Journal of Applied Physics, 43 (1972) 1347.
S02-P18 Dendritic Growth Kinetics in Undercooled Melts under Static Magnetic Fields
Gao, Jianrong*1, Kao, Andrew2, Pericleous, Koulis2, Galenko, Peter K.**3, Alexandrov, Dmitri V.4
1Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, Shenyang 110819 (People’s Republic of China) 2Centre of Numerical Modelling and Process Analysis, University of Greenwich, London SE10 9LS (United Kingdom) 3Department of Physics and Astronomy, Friedrich Schiller University of Jena, Jena 07743 (Germany) 4 Department of Mathematical Physics, Ural Federal University, Ekaterinburng 620000 (Russian Federation) *email: [email protected]; **email: [email protected]
Dendritic growth from undercooled melts has been intensively studied over the past seventy years. Current attention is focused on the effect of fluid flow on dendritic growth, which has been long assumed to be responsible for a discrepancy between theory and experiment in the low undercooling region [1]. Recently, a new theory was proposed to describe dendritic growth kinetics with melt convection at arbitrary Peclet numbers [2]. This new theory, termed Alexandrov-Galenko theoy (AG theory for short), has a potential to account for a broad range of experimental data, but has not been fully testified yet. This paper presents measured dendritic growth velocities in pure nickel samples of different purity under static magnetic fields of intensities up to 6 T. The measured growth velocities show strong dependences on the intensities of the static magnetic fields for undercoolings below 100 K. This variation can be attributed to both the modification of residual bulk flow and the introduction of thermoelectric magnetohydrodynamics (TEMHD). The measured growth velocities were modeled using the AG theory by assuming magnetic field-tuned fluid flow velocities. TEMHD in dendritic growth was modeled using an enthalpy-based method [3] to have insights into the flow-dependent growth kinetics. The numerical simulation shows a good agreement with the experimental observations and the analytical modeling. The effects of impurities on TEMHD and dendritic growth kinetics are discussed.
Figure 1. Dendritic growth velocities of pure nickel (99.999% purity) as a function of undercooling. The solid circles shows the measured data under a static magnetic field of B = 2 T. The solid line shows the calculated data using the AG theory [2] assuming an incident flow velocity of U = 1.0 m/s.
References: [1] Funke O., Phanikumar P., Galenko P. K., Chernova L., Reutzel S., Kolbe M., Herlach D.M., J. Cryst. Growth 297 (2006) 211. [2] Alexandrov D.V., Galenko P.K., Physics-Uspekhi, 57 (2014) 771. [3] Kao A., Pericleous K., Magnetohydrodynamics, 48 (2012) 361.
S02-P19 Multiphase-field theories of crystallization: A comparative study Gyula I. Tóth*1,2, Tamás Pusztai2,Bjørn Kvamme1, László Gránásy2,3
1Department of Physics and Technology, University of Bergen, Allégaten 55, 5007 Bergen (Norway) 2Wigner Research Centre for Physics, P.O.Box 49, 1525 Budapest (Hungary) 3BCAST, Brunel University, UB8 3PH Uxbridge, Middlesex (United Kingdom) *email: [email protected]
We present a comparative study of the most widespread, free energy functional based multiphase- field theories, a technique used in modelling multicomponent and/or polycrystalline solidification. Focusing on physical consistency, first we set up a list of both equilibrium and dynamic criteria, and put several multiphase theories to this test. We show that even if planar two-phase interfaces are at least numerical stationary solutions of the dynamic equations, they do not represent equilibrium, i.e. they are not the solution of the general Euler-Lagrange equations in most of the existing multiphase theories. In the rest, the planar interface = stationary solution compatibility is established either by leaving the energy functional formalism for large number of phases or limiting ourselves to 3 phases. The latter also prescribes additional conditions for the form of the free energy functional, and we are also not free in choosing equilibrium interfacial properties.
In order to resolve the problems of existing multiphase descriptions, we combine the successful elements of the investigated approaches with a recently developed mobility matrix, together with proposing a new free energy functional. The result is a new, general multiphase description for arbitrary number of phases (or components), which (i) keeps the variational formalism, together with (ii) showing natural reduction in the lack of a phase (or component) on the level of both the free energy functional and the dynamic equations, (iii) using arbitrary (even anisotropic) pairwise equilibrium interfacial properties, (iv) penalizing high-order multiple junctions, (v) showing equilibrium stationary compatibility, (vi) avoiding the appearance of spurious phases on two- phase interfaces, and (vi) showing numerical method independent results.
Our new model has been tested against (fluid-flow coupled) multi-component spinodal decomposition as well as multi-dendritic solidification, thus demonstrating the robustness of the theory.
Figure 1. Fluid-flow assisted spinodal decomposition in a ternary liquid.
References: [1] G. I. Tóth, T. Pusztai, L. Gránásy, to be submitted. [2] G. I. Tóth, B. Kvamme, to be submitted.
S02-P21 Thermoelectric Control of Crystal Growth
Kao Andrew1, Pericleous Koulis1
1Centre of Numerical Modelling and Process Analysis, University of Greenwich, London SE10 9LS (United Kingdom) email: [email protected]
It is known that an electric potential exists at the junction of two materials in the presence of a thermal gradient. This, Seebeck effect, describes how the potential (ΔΨ) forms, when two materials with varying Seebeck coefficients (S) are placed in thermal contact, and that at the boundary this e.m.f varies with interface temperature. In a conducting melt, the current J is given by the generalised form of Ohm’s law for moving media J E u B ST , which includes the Seebeck contribution. At the material interface the potential difference can then be written as ST . When this concept is applied to the evolution of a growing dendrite [1], the interfacial temperature (Ti) can be defined by the Gibbs-Thompson condition:
i , Tm i T T mC C , where the second term m H 0 l accounts for local free energy through surface energy anisotropy (a) and curvature and the final term accounts for solute partitioning in binary alloys. This equation leads to a local variation in surface temperature and the formation of thermoelectric (TE) currents, which are therefore an inherent part of solidification. When an external magnetic field is applied to this situation, the TE currents interact with it to induce solutal convection at the material interface, giving rise to the phenomenon of TE magneto-hydrodynamics (TEMHD) first named by Shercliff [2]. The resulting transport of mass alters the thermal and solutal fields surrounding the dendrite, leading to changes in morphology. These changes, which have been observed experimentally [3], have been modelled by the authors using a 3D phase-field variant, which allows the effects of convection [1]. This contribution (b) demonstrates how crystal morphology can be tailored, by varying Figure 1: (a) Normal the strength and direction of the applied magnetic field as shown in isothermal dendritic growth the figure 1(b), for a z-directed field Bz. of a binary alloy, and (b) model-predicted disrupted References: [1] Kao A., Pericleous K., Magnetohydrodynamics, 48 (2012) morphology when a strong [2] Shercliff J A, “Thermoelectric Magnetohydrodynamics,” J. Fluid magnetic field acting along Mech. 91, 231 (1979) the Z direction is applied. [3] Yasuda H et al. “Influence of the Static Magnetic Field on Dendritic / (TN-normalised surface Columnar Solidification, Observed by X-ray Imaging” Proc Light Metals temp-erature) TMS 2015
S02-P22 Orientation-field model for polycrystalline solidification in binary alloys with a singular coupling between order and orientation
Bálint Korbuly1, Tamás Pusztai,1 László Gránásy1,2
1Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, P.O. Box 49, Budapest H- 1525, Hungary 2BCAST, Brunel University, Uxbridge, Middlesex, UB8 3PH, United Kingdom
In order to model polycrystalline solidification in binary alloys, we have adopted a new orientation field model of Henry et al. [1] based on a singular coupling between the square gradient of the orientation field and the phase field. Extending the orientation field to the liquid phase as in previous work [2] (where it is made to fluctuate in time and space) and employing an economic model for foreign particles, we capture phenomena like homogeneous nucleation of growth centres, and the formation of new grains at the growth front (growth front nucleation), multi-dendritic solidification, dizzy dendrites, and polycrystalline seaweed structures. We also investigate grain coarsening phenomena, and compared the model's predictions with existing models and experiments.
Figure: A dendrit, a spherulite and a snapshot of grain coarsening
[1] H. Henry, J. Mellenthin, and M. Plapp: Orientation-field model for polycrystalline solidification with a singular coupling between order and orientation. Physical Review B 86, art. no. 054117 (2012).
[2] L. Gránásy, L. Rátkai, A. Szállás, B. Korbuly, G.I. Tóth, L. Környei, and T. Pusztai: Phase-field modeling of polycrystalline solidification: From needle crystals to spherulites – a review. Metall. Mater. Trans. A 45, (4) 1694-1719 (2014). Open access.
S02-P23 Rotationally-driven, axisymmetric oscillatory convection in a semitransparent Czochralski melt model Reza Faiez*, Yazdan Rezaei 1 Solid State Lasers Department, Laser & Optics Research School, Tehran P.O. Box 11365-8486, Iran *email: [email protected] Thermal striations are commonly assumed to be caused by convective instabilities and temperature fluctuations at the crystallization front. In the present hydrodynamic modeling of Cz/Gd3Ga5O12 melt, time-dependent Navier-Stokes equations were solved for an axisymmetric fluid flow in a cylindrical crucible with rc=60 mm, as the melt characteristic length, and hc=2rc as the melt height. The crucible wall is at a constant temperature Tw=Tmp+ΔTmax , and it is assumed to be an opaque and gray surface (ε=0.5) diffusely emitting and reflecting thermal radiation. The melt absorbs and emits but not scatter radiation, and its optical properties (n=1.938 and a=0.1m-1) are independent of temperature and wavelength. The melt free surface, with a meniscus configuration at the crystal periphery, is a semitransparent diffuse-gray surface. The crystal (rx=24mm) is simulated by a rotating plane surface (Tx=Tmp; ε=1) inclined toward the melt as a convex to melt interface. Energy is transmitted through the melt surface to radiatively black ambient walls at constant temperature, Ta=Tmp - ΔTmax . Depending on the crystal-rotation rate, Ω (rad/s) strictly periodic 3 flow was observed in the melt characterized by Pr=4.69, Gr=(1.142×10 ) ΔTmax and 2 2 Re=5.085×10 Ω, and without Marangoni effect, Ma=(1.682×10 ) ΔTmax , where ΔTmax=108K is the driving temperature differences. Assuming that the rotationally-driven forces are approximately equal to the buoyancy forces at 2 Gr . Pr ≈ Re , a significant change in the period of oscillating flow, tp(s) is expected at around Ω~1.50. As shown in Fig.1, the convective flow remains steady for Ω<1.15 (tp=0). Increasing the rotation rate, 1.15≤Ω≤1.50, the flow becomes an axisymmetric oscillatory one exhibiting a cold plume descending from the crystal periphery along the rotation axis toward the crucible bottom.
Figure 1. Numerical results of the period of temperature oscillation and maximum stream function with crystal rotation rate
Due to a relatively low Pr number, the melt flow is reheated before the cold plume descends fully to the crucible bottom. The period of oscillations, tp found to be almost abruptly increased to its maximum value of ~20s at Ω ~ 1.5 rad/s. From the tp(Ω) curves, the Marangoni effect has a suppressing effect on the oscillatory flow for the range of 1.2<Ω<4.0, so that the tp,max decreased from ~20s to ~11s in the presence of thermocapillary forces. Striation distances, ds can be estimated by ds= vztp where vz is the crystal pulling rate, and the frequency of oscillations in the vicinity of the 2 crystallization front is given by ω=(1/tp)(δT /α) where δT is the thermal boundary layer thickness and α is the thermal diffusivity of the melt. Hence, tp,max corresponds with the lowest frequency of thermal fluctuations and largest striation distances, which affect the crystal homogeneity much more than do the high-frequency ones.
S02-P24 Thermal stability and spontaneous breakdown of free-standing metal nanowires Bogdan Ranguelov1, Paraskevas Giazitzidis2, Panos Argyrakis2, Michail Michailov*1
1Institute of Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria) 2Aristotle University of Thessaloniki, Thessaloniki (Greece) *email: [email protected] Recently we have suggested a new physical model for spontaneous, hole-mediated breakdown of metal monatomic nanowire located on crystal surface (M. Michailov, D. Kashchiev, Physica E 70 (2015) p. 21–27). The physical scenario of breakdown process implies three consecutive steps of nanowire rupture including (i) formation of active atoms, (ii) generation of single atomic vacancy and (iii) evolution of single vacancy into an unrecoverable vacancy cluster (hole). In all these steps preceding and finally causing the nanowire rupture, the impact of the substrate is significant. The substrate could act on nanowire stability in two directions. It can stabilize or in contrast it can facilitate the nanowire rupture depending on different factors as the anisotropy and softness of the surface potential, lattice misfit between substrate and nanowire atomic arrangement, etc. These competing processes are operated by the substrate/nanowire interface energy minimization. Since a large number of experiments deal with nanowire features on a substrate, the evaluation of substrate contribution on nanowire stability is essential. Therefore, the knowledge of thermodynamic behavior of a free-standing or nanowires not affected by any external forces is important. Does the vacancy and hole formation model is valid solely for epitaxial interfaces? In the present study, grounded on continuous space Monte Carlo atomistic simulations, we discuss this problem analyzing the thermal behavior of free metal monatomic chain for which the influence of the substrate is entirely avoided. The extensive atomistic simulations demonstrate that free-standing nanowire follows more elementary mechanism of rupture. The formation of a single atomic vacancy causes non-recoverable nanowire breakdown. Hence, because of the missing stabilization role of the interface the rupture kinetics is much faster. Describing this kinetics via rate equations, we evaluate some important time- and temperature-dependent physical features of the free-standing nanowire as mean lifetime τ, number of vacancies Nv(t), and the probability Pv(t), for generation of at least one vacancy until time t, Figure 1. Hence, providing insight into the mechanism and kinetics of spontaneous thermal rupture of a free monatomic metal nanowire, the present study reveals the degree of validity of the hole-mediated nanowire breakdown mechanism.
Figure 1. Temporal evolution of Cu free-standing nanowire at 10 K at 0 (upper atomic chain), 600, 1100, 1600 Monte Carlo Steps
S02-P25 Towards the understanding of hydrozincite precipitation; Population balances on sparingly soluble compounds.
Martín-Soladana Pablo M. 1, Lai Xiaojun 1, York David 1, Buchkremer Anne 2, Granito Nathalia 2,Wise Geoff 2. Xu Dan 2,Martín-de-Juan2Luis.
1Institute of Particle Science and Engineering, School of Chemical and Process Engineering. University of Leeds, LS2 9JT, UK. 2Procter & Gamble Co. Newcastle innovation centre. Newcastle. United Kingdom email: [email protected]
The control of particle size in reactive crystallization is of interest, among others, to pharmaceutical, catalyst and cosmetic industries. In this work, the contributions of nucleation growth and aggregation to the final particle size distribution (PSD) were resolved for the case of hydrozincite, a sparingly soluble compound important for its high surface area and for being a precursor of zinc oxide. Population balance models (PBM) and momentum theory, as proposed by Jones et al.[1] , were, used to study the influence of the associated process parameters, such as pH, shear rate and concentration over the final PSD. The kinetic parameters (nucleation rates, growth rates and aggregation kernels) were obtained by optimizing the model to the experimental PSD data. The particle size distribution was obtained by static light scattering and FBRM. The particles were further characterized by measuring the Zeta potential, X-ray diffraction and microscopy techniques. STEM and XRD show primary particles from 8 to 25 nm arranged in compact aggregates with fractal dimensions from 1.7 to 2.7 and sizes of 7-50 µm as light scattering and SAXS measurements shows. More dispersed aggregates were found at lower pH. This was attributed to the higher surface charge shown by zeta potential measurements. The results of this study are of potential used in the design of crystallizers and to improve the knowledge on population balance.
Reference: [1] Jones, A. G., Hostomský, J., & Wach, S. (1996).. Chemical Engineering Communications, 146(1), 105–130.
S02-P26 Effects of boundary conditions and geometry on structural and thermodynamic properties of modeled semiconductors
Natalia Podolska*1,2
1Saint-Petersburg Branch of Joint Supercomputer Centre, 26 Politehnicheskaia str., Saint-Petersburg (Russia) 2Ioffe Institute, 26 Politehnicheskaia str., Saint-Petersburg (Russia) *email: [email protected]
Understanding of behaviour and properties of semiconductor materials at different scales (bulk, films, nanostructures etc.) is a key question for developing of semiconductor technologies and modelling of crystal growth and structures (heterstructures, quantum dots etc.) [1,2,3]. In the paper, we present the numerical analysis of effects of boundary conditions and geometry (size, shape etc) on structural and thermodynamic properties of wurtzite and zinc blende II-VI and III-V ternary compounds. To find the structural and thermodynamic properties, the simulations have been carried out with a modified valence force field method and models, based on some ideas described in [4]. The use of multiple computation runs was used to improve the representative statistics of the valence force field computations, which is necessary for an accurate prediction of properties and their composition dependences [4]. Interatomic distances (anion-cation, anion-anion and cation-cation) and thermodynamic properties (mixing energy, interaction parameter, enthalpy of mixing etc) will be presented as functions of sizes, scales (from bulk to thick and thin films, wires or columns) and shapes (films with different thickness, cubes, columns with parallelogram and diamond-shaped cross-sections). Good agreement with the experimental data was demonstrated. Moreover, the simulation results were compared with results obtained by other methods. The reported study was partly supported by RFBR (Russian Foundation for Basic Research), research project for young researchers No.14-08-31581.
Number of atoms 10 100 1k 10k 100k Periodic BC In-As Ga-As 4 In Ga As Free 0.5 0.5 N =512 a 3 0.38
Free (kJ/mol) kJ/mol m
N =2744 E 1.55 kJ/mol a 2
Counts
1 Periodic BC Free BC
Mixing Energy Mixing Energy E @N =110592 0 m a 2.40 2.45 2.50 2.55 2.60 2.65 2.70 10-17 10-16 10-15 2 Anion-Cation Distance (A) Surface Area (m ) Figure 1. Ga-As and In-As distances (left) in zinc blende In0.5Ga05As as well as mixing energy as a function of surface area (right). Shape of modeled crystals is cube. "Free" denotes that "free surface" and "Periodic" denotes that periodic (bulk crystal) boundary conditions were used. "Na" is the number of atoms in the modeled crystals. Vertical arrows (right) denote differences between values of the mixing energy.
References: [1] Joyce H.J., Gao Q., Tan H.H., Jagadish C., Kim Y. et al., Progress in Quantum Electronics 35 (2011) 23 [2] Porte L., Journal of Crystal Growth 273 (2004) 136–148 [3] Guisbiers G., Nanoscale Res Lett (2010) 5 1132–1136 [4] Karpov S., Podolskaya N., Zhmakin I., and Zhmakin A., Phys.Rev.B 70 (2004) 235203
S02-P27 The Conductivity Of Two-Dimensional Electron Crystal On The Surface of liquid 4He. Modeling.
Syvokon Vitalii 1, Nasyedkin Kostyantyn 2, Sharapova Iryna*1
1B.Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine, 47 Lenin Ave., Kharkov 61103 (Ukraine) 2 RIKENCEMS, Hirosawa 2-1, Wako 351-0198, (Japan) *email: [email protected]
The surface electrons over liquid helium (Wigner crystal) is a spatially ordered state of a two- dimensional system of classical particles with the Coulomb interaction. Ordering occurs when the ratio between the potential and kinetic energies (plasma parameter Г) of the particles exceeds a certain value (Г > 130). The order-disorder transition in this system is a Berezinski-Kosterlitz- Thouless-type phase transition. The phase transition can be observed while investigating the transport characteristics of the electron layer (complex conductivity) which are different in the ordered and disordered states. When the crystal is exposed to an external electric field directed along the surface of the liquid (guiding field), the layer conductivity varies nonmonotonically with the increasing field. In the limit of high guiding fields both the components of the crystal conductivity are close to the conductivity of a disordered electron layer. It is found [1] that the conductivity of a Wigner crystal changes drastically as the holding potential decreases. The active part of the conductivity was observed to change sharply in a narrow interval of compressing voltages, which suggests a possible transition in the system. The reactive part of the conductivity was varying smoothly. The process observed could hardly be related either to melting, because it occurred much below the melting temperature, or to a dynamic transition, because the measurement was made in low guiding fields. The sharp changes in the conductivity may be accounted for by the disturbance of the crystalline order when the holding field decreases and a solid disordered phase is formed. “Evaporation” of the electrons onto the higher-lying surface levels was assumed as a possible mechanism in [2]. This study is a continuation of the investigation of the electron crystal conductivity under the condition of a decreasing holding potential. The model calculation suggests another possible reason for the observed behavior of the conductivity. The modeling was reduced to calculating a possible configuration of the electron after their redistribution provoked by the compressing field. A correlation density function was calculated to characterize the degree of ordering of the electrons. The modeling results show that a decrease in the holding field causes redistribution of the electrons. As a result, their surface density increases in the direction from the center of the layer towards its edge though a certain order of the electron arrangement still persists. Besides, it is found that the active part of the conductivity increases sharply even with a slight decrease in the holding potential, i.e. the resistance of the layer increases.
References: [1] Nasyedkin K. A., Syvokon V. E., Neoneta A.S., Pisma v ZhETF, 91 (2010) 652. [2] Slavin V. V., Krivchikov A. A., Fiz. Nizk. Temp., 38 (2012) 1390.
S02-P28 Transitions between regimes of crystal growth kinetics under decaying supersaturation
Vesselin Tonchev*1,Christo Nanev1, Georgi As. Georgiev2, Peter Vekilov3
1Institute of Physical Chemistry, Bulgarian Academy of Sciences, 11 Acad. Georgi Bonchev str., Sofia (Bulgaria) 2Faculty of Biology, University of Sofia “St. Kliment Ohridski”, 8 Dragan Tsankov blvd.. Sofia (Bulgaria) 3Department of Chemical Engineering, University of Houston, Houston, TX 77204-4004(USA) *email: [email protected]
Numerous industrial and laboratory processes involve the precipitation of crystals during which solute is not supplied, thus supersaturation decays in time. This may induce a transition between different regimes of crystal growth that needs to be accounted in crystallization models of particle size and distribution. In order to model the transition between regimes of crystal growth we assume g that the normal growth velocity is rSgg where g is a kinetic coefficient and S is the supersaturation. The growth rate is defined as twice the normal velocity (in units of the g=1 normal
rg g g g1 velocity) GBgg22, S/S0 is the normalized supersaturation and BSg 0 . The 10S 1 different kinetic regimes are characterized by their respective values of the kinetic exponent g. Following the “morphology selection principle” [1] we assume that if two growth regimes with kinetic exponents g1 and g2 are simultaneously available in the system, the growth starts with the faster one. We show that in this case, if the growth starts from the regime with g1, transition into a regime with g2 is possible only if g1>g2, fig. 1a. Thus, in order to have transition into a regime with higher value of g this should become available at some value of the decreasing supersaturation; this transition is illustrated with experimental data on the crystallization of Ni in fig.1b. These findings will contribute to the refinement of models of batch crystallization aimed at predicting the properties of the crystal population and the kinetics of crystal synthesis.
a b Figure 1. Two possible transitions along the decaying (normalized)supersaturation: (a) both regimes with g1=2 and g2=1 are available from the beginning of the growth; (b) growth starts with g1=1 and then in certain point of supersaturation another regime with g2 = 2 appears
References: [1] Ben-Jacob E., Contemporary Physics, 34 (1993) 247. [2] Dimitrov V., J. Crystal Growth, 76 (2003) 504.
S02-P29 EFFECT OF SURFACE RECONSTRUCTION ON Ge‐Si(001) HETEROEPITAXY Paramita Ghosh Indian Institute of Technology Kanpur, Kanpur‐208016, India
The most widely studied heteroepitaxial system is Ge on Si(100), due to its ease for integration with Si-based devices. The (100) surface of Silicon shows several reconstructions, of which the 2 × 1 is the most relevant for growth at high temperature in Molecular Beam Epitaxy (MBE). Surface reconstruction changes the nature of bonding on the surface inducing additional anisotropies in surface energy and affects properties of the growing film. We have developed a two component three dimensional solid-on-solid model on simple cubic lattice, with necessary modifications to account for surface reconstructions. Additionally, the elastic effects due to lattice mismatch between the film and the substrate are modeled using a harmonic ball and spring model of elasticity. This model ables to explain most of the features of Si on Si(001) homoepitaxy like dimer chain formation, island size and shape distribution and their dependence on temperature[1]. In the case of Ge on Si(001), this model is able to reproduce strain induced effects like dimer chain vacancy formation and alignment of vacancies around 1ML coverage[2]. In this study we have revealed how elastic effects, coupled with reconstruction can explain the observed behavior at the early stages of growth of Ge on Si(001). We have extended the simulations to multilayer growth to study how reconstruction plays a role in the 2D/3D growth transition. Our goal here is to see if it can be used to accurately predict formation and shapes of quantum dots which are formed during Stranski-Krastanov growth. References [1] P.Ghosh, M. Ranganathan, Surf. Sci. 630 (2014) 174. [2] P. Ghosh, P. Nath and M. Ranganathan, Surf. Sci. 639 (2015) 96.
S02-P30 Interatomic distances and thermodynamic properties of wurtzite and zinc blende AlInGaN
Natalia Podolska*1,2
1Saint-Petersburg Branch of Joint Supercomputer Centre, 26 Politehnicheskaia str., Saint-Petersburg (Russia) 2Ioffe Institute, 26 Politehnicheskaia str., Saint-Petersburg (Russia) *email: [email protected]
Materials based on quaternary III-V semiconductor alloys, such as AlInGaN, are very inportant for developing of modern micro- and optoelectronics. At the same time, there is a lack of experimental data and theoretical information on structural (interatomic distances) and thermodynamic properties of these quaternaries. So, numerical simulations seem as the most informative and direct way of obtaining this information. In the paper, we present simulation results and analysis of the structural (anion-anion, cation- cation, anion-cation) and thermodynamic properties (mixing energy and thermodynamic functions) of bulk wurtzite and zinc blende AlxInyGa1-x-yN as a function of compositions 'x' and 'y'. To find the structural (anion-cation, cation-cation and anion-anion) and thermodynamic (mixing energy, enthalpy and entropy of mixing, spinodal decomposition) properties dependence on a function of compositions, the simulations have been carried out with the modified valence force field method and some ideas described in [1], adapted for quaternary alloys. The multiple computation runs was used to improve the representative statistics of the valence force field computations, which is necessary for an accurate prediction of properties and their composition dependences [1]. Analytical approximation of mixing energy as a function of compositions 'x' and 'y' in AlxInyGa1-x-yN will be presented. Using the approximation, thermodynamic properties of the solid solution such as enthalpy and entropy of mixing, spinodal decomposition will be described. Good agreement with the experimental data was demonstrated. The reported study was partly supported by RFBR (Russian Foundation for Basic Research), research project for young researchers No.14-08-31581.
Figure 1. Mixing energy in kJ/mol of wurtzite AlxInyGa1-x-yN as a function of compositions 'x' and 'y'.
References: [1] Karpov S., Podolskaya N., Zhmakin I., and Zhmakin A., Phys.Rev.B 70 (2004) 235203 [2] Monroy E., Gogneau N., Enjalbert F., Fossard F., Jalabert D., Bellet-Amalric E., Le Si Dang, Daudin B., J. Appl. Phys. 94 (2003) 3121
S02-P31 A numerical model on nano-line patterning of c-plane sapphire substrates for selective area growth of AlN islands
I. Davis Jacob, A. Rosy, G.K.Priya Merline, K. Prabakaran, K. Baskar and M. Chitra*
Crystal Growth Centre, Anna University, Chennai (India) *email for correspondence : [email protected], [email protected]
Abstract: A simple numerical model of nanopatterning of c-plane sapphire substrates for selective area growth of AlN islands is proposed. This is to reduce the threading dislocations on the GaN epitaxial layers arising due to lattice mismatch between GaN and sapphire. Lattice constant of sapphire is greater than that of GaN whereas the lattice constant of aluminium nitride is less than that of GaN. When the two lattices of sapphire and AlN are alternated periodically on the surface of the c-plane substrate, the lattice mismatch between the GaN and alternating sapphire/AlN substrate is reduced laterally on the c-plane interface. This will have a tremendous impact on the quality of the GaN epitaxial layers formed on the substrate. The dislocation density on the GaN epitaxial layers is expected to decrease due to better lattice matching conditions. A simple numerical model is proposed based on the origin of line dislocations in a given direction (One Dimension) and in a given area (Two Dimensions). It is found that a minimum of one line dislocation would arise laterally on the (c-plane) interface of GaN-sapphire beyond an atomic distance of five lattices of sapphire whereas a line dislocation on the (c-plane) interface of GaN-aluminium nitride would arise beyond 40 lattices of aluminium nitride in a given direction. The theoretical ratio of sapphire and AlN lattices in a given direction and that in a given area are estimated for minimum dislocation conditions. Sapphire can be patterned or etched periodically in the shape of wells (line-patterning) on the c-plane surface for selective area growth of AlN. The periodicity, line-patterning density and sizes (width of wells) of the aluminium nitride islands were estimated.
S02-P32 Modeling of axial heterostructure formation in multicomponent III-V nanowires
Koriakin Aleksandr*1,2, Sibirev Nikolai1,2, Dagou Zeze2,3, Dubrovskii Vladimir1,2
1 St. Petersburg Academic University, Khlopina 8/3, St.Petersburg (Russia) 2ITMO University, Kronverkskiy pr. 49, St. Petersburg (Russia) 3School of Engineering and Computing Sciences, South Road, Durham (UK) *email: [email protected]
Heterostructure nanowires (NWs) have a wide range of potential applications in opto- and nanoelectronics where the presence of an abrupt heterojunction is highly desirable for designing devices with high-performance characteristics. Vapor-liquid-solid (VLS) growth is probably the method most used to synthesize NWs because it facilitates the formation of relatively sharp interfaces for several III-V semiconductors, elements from group V may be easily interchanged (e.g. InAsP/InAs, GaAsP/GaP [1]). In turn, the formation of abrupt interfaces is much more difficult when elements from group III are interchanged (e.g. for AlAs/GaAs, GaInAs/InAs, InGaAs/GaAs[1]). This difference of interface sharpness has been explained by the fact that solubility of group III atoms in the catalyst droplet (10-40%) is usually higher than that of group V atoms, e.g. arsenic and phosphor (1-6%). Despite the variety of experimental data, theoretical studies of heterojunction formation in NWs are very limited. Moreover, only a small set of materials can be considered within the assumptions made. In this paper, we propose a model describing heterostructure formation in ternary III-V NWs grown by catalytic VLS method. Our approach is based on the determination of chemical potentials of dissolved materials using the regular solution model and the Stringfellow formula for the computation of the interaction coefficients of species present in the droplet [2]. The model allows the estimation of the heterojunction width dependence on the growth temperature. This dependence has not been reported before by any previous theoretical studies. The AlGaAs/GaAs heterojunction formation in the Au-catalyzed AlGaAs NWs was considered as an example of ternary system. The heterojunction width was found to increase with the growth temperature with a second-order polynomial dependence (Figure 1).
Figure 1. AlGaAs/GaAs heterojunction width as a function of the growth temperature.
References: [1] Messing M. et al., Nano Lett., 11 (2011) 3899 [2] Glas F., Appl. Phys., 108 (2010) 73506
SESSION 3 Product and Process Design of Pharmaceuticals and Fine Chemicals
Using crystal growth to generate single chirality from an achiral start
Rene Steendam1, Jorge Verkade1, Tim van Benthem1, Hugo Meekes1, Willem van Enckevort1, Jan Raap2, Floris Rutjes1, Elias Vlieg1
1Radboud University, Institute for Molecules and Materials, Nijmegen, The Netherlands 2Leiden Institute of Chemistry, Leiden University, The Netherlands *email: [email protected]
In recent years the process of Viedma ripening, in which a racemic mixture of enantiopure crystals is ground, has been found to be an effective and elegant way to deracemize a chiral compound [1]. Here we show that a combination of an organic reaction with Viedma ripening leads to the remarkable result that from fully achiral starting conditions, an end state of single chirality can be reached in a single process [2]. This approach not only provides more insight into the origin of homochirality in life but also offers a pathway to acquire enantiopure compounds for industrial applications.
Figure 1. A schematic showing that a chemical reaction of achiral starting material first leads to a mixture of left and right-handed crystals (red and blue), that subsequently transform to single chirality.
References: [1] W.L. Noorduin et al., Angew. Chem. Int. Ed. 48 (2009) 9600. [2] R.R.E. Steendam et al., Nature Commun. 5 (2014) 5543.
Crystallisation Characteristics of an Organic Material in Industrial Mother Liquor with Impurities
Khan Shahid 1, Mahmud Tariq*1, Roberts Kevin 1, Zhu Xiaofeng 1, George Neil2 and Sillers Pauline2
1Institute of Particle Science and Engineering, School of Chemical and Process Engineering, The University of Leeds, Leeds LS2 9JT, UK 2Syngenta, Jealott's Hill International Research Centre, Bracknell, Berkshire RG42 6EY, UK
In pharmaceutical and fine chemical industries, the isolation and purification of organic materials are commonly carried out using various solution crystallisation techniques including the batch cooling crystallisation process. In industrial crystallisation processes, mother liquors usually contain unwanted dissolved molecules (generally referred to as impurities) produced via reaction steps prior to the crystallisation and their concentration may vary from batch to batch. It has long been established that the supersaturation driven nucleation and crystal growth rates can change profoundly even in the presence of low levels of impurities added intentionally to or inherently present in the solution, and thus affects the size, shape and purity of the product crystals. This could also impede efficient downstream processing of crystals such as filtration, drying and milling. In order to control industrial crystallisation processes to meet product specifications, such as narrow crystal size distribution, high chemical purity and desired crystal morphology, with high product yields, it is important to develop a detailed understanding of the crystallisation characteristics of product materials in the mother liquors containing process generated impurities. This can be achieved via replicating the industrial process at laboratory scales in the presence of impurities. The work reported here investigated the crystallisation behaviour of an organic material (referred to as compound A due to confidentiality) from an industrial mother liquor (which mainly contains an organic compound), corresponding pure solvent and the pure solvent doped with the process generated impurity as a function of representative processing variables, e.g., level of impurities, seeding and cooling profile. Experiments were carried out in a 500 mL jacketed glass stirred tank crystalliser with temperature controlled using Julabo FP50-HD thermostatic bath. The metastable zone width and induction time for the nucleation of compound A were determined using a turbidimetric method as a function of both cooling rate and solute concentration in the pure and in impurity added solvent. ATR-FTIR spectroscopy coupled with a PLS calibration model was used for on-line monitoring and control of supersaturation during the batch cooling crystallisation of compound A. The metastable zone width was found to be wider in the mother liquor and in the solvent doped with impurity compared with that in pure solvent. The induction time for nucleation of compound A increases with increasing impurity concentration. A significant outcome of this research is reflected in the observations that the crystals produced in pure solvent have a much different physical form compared to those crystallised from mother liquor. The former crystals tend to be smaller and heavily agglomerated when compared to the latter which display superior crystal quality and external morphology. The latter perhaps is a reflection of the nucleation and solubilisation abilities of the other components present in the mother liquor. However, in the pure system, particles spontaneously nucleated at much higher supersaturation levels leading perhaps to an excessive primary nucleation rate resulting in smaller and more agglomerated crystals.
Preferential Orientation of β-phase Triacylglycerol on Graphite Surface
Fumitoshi Kaneko1*, Shinichi Yoshikawa2, Haruyasu Kida2, Kiyotaka Sato3
1Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka (Japan) 2R&D Division for Future Creation, Fuji Oil Co., Ltd., Tsukubamirai, (Japan) 3Hiroshima Univeristy, 1-4-4, Higashihiroshima (Japan) *email: [email protected]
In order to promote the lipid crystallization, surfactants and materials having long hydrocarbon chains have been used as additives. It is considered that their alkyl chains act as templates for the heterogeneous nucleation by ordering the hydrocarbon-chain moieties of lipids. Recently, it has been clarified that inorganic and organic crystals (i.e., talc, graphite, carbon nanotube, theobromine, terephthalic acid, and ellagic acid dihydrate) remarkably promoted the lipid crystallization to form thermodynamically stable crystals [1, 2]. These additives are sparingly soluble in lipids and possess no long hydrocarbon chains in their molecules; therefore, we assume that the promotional effects are caused by the strong intermolecular interactions between the surfaces of the crystalline materials and lipids. To understand the mechanism of this type of heterogeneous nucleation, we launched an investigation of the molecular orientation in trilaurin (LLL) crystals generated on the flat hexagonal net plane of a graphite sheet. In this study, the orientation of the LLL β-form crystals generated on the surface of a graphite sheet was examined by X-ray diffractometry (XRD) and polarized Fourier transform infrared– attenuated total reflection (FTIR–ATR) spectroscopy. Figure 1 shows the XRD profile taken under the condition that the scattering vector is parallel to the normal of the graphite sheet. There appear the intense 00l reflections due to the long spacings of LLL β-form crystals, whereas the reflections due to the subcell structure (T//) in the 2θ region of 19-24° are significantly week, suggesting that the lamellar planes of the LLL crystals were parallel to the surface of the graphite sheet. Figure 2 shows the polarized FTIR-ATR spectra, where the p- and s-polarized spectra emphasize the components of transition moment normal and parallel to the sample surface, respectively. The p- polarized spectrum shows CH2 wagging progression bands much more intense than those in the s- polarized spectrum. Since the transition moments of the wagging modes are parallel to the long hydrocarbon chains, the ATR spectral feature is consistent with the model obtained by XRD experiments. These results indicate that the heterogeneous nucleation of the LLL β-form crystals takes place with the lamellar orientation parallel to the surface of the graphite sheet.
Figure 1. XRD profile of LLL β Figure 2. Polarized FTIR–ATR spectra of LLL β References: [1] Shinichi Yoshikawa, Haruyasu Kida, Kiyotaka Sato, J. Oleo Sci., 63 (2014) 333-345 [2] Shinichi Yoshikawa, Haruyasu Kida, Kiyotaka Sato, Eur. J. Lipid Sci. Technol., 117 (2015) in press.
Crystallization of L-Glutamic acid polymorphs in stirred and stagnant conditions
Tahri Yousra*1,2, Gagnière Emilie1, Chabanon Elodie 1, Bounahmidi Tijani2, Mangin Denis1
1Université de Lyon, Université Claude Bernard Lyon 1, CNRS, UMR 5007, LAGEP, 43 Boulevard du 11/11/ 1918, 69622 Villeurbanne (France) 2Ecole Mohammadia d’Ingénieur LASPI, Avenue Ibnsina, 10765 RABAT (Morocco) *email: [email protected]
This work deals with the study of the polymorphism of L-Glutamic acid (LGlu) which can crystallize in two known monotropic polymorphs: the stable form β with needle like shape and the metastable form α with prismatic shape [1]. Since the β form can generate many difficulties in production, transport and storage [2] it is more suitable to produce α form. Two experimental devices were used. Cooling crystallizations in water were performed in both a stirred double jacketed vessel of 2 L and a non-agitated thermostated cell of 4 mL. The crystallization was monitored in situ by a video probe in stirred conditions and by a microscope in stagnant conditions. Effect of temperature and supersaturation on the polymorphism of LGlu was investigated. In stirred conditions, at low supersaturation, the effect of temperature was relevant: at high temperatures only the stable form β nucleated while almost only the metastable form α was observed at low temperatures. At high supersaturation, both polymorphs crystallized with high percentage of α at low temperatures (around 10°C) and high percentage of β at higher temperature (around 45 °C).These results suggest that LGlu polymorphism is strongly affected by temperature and does not obey to the Ostwald rule of stages. It was also observed the β polymorph habit changed with supersaturation. At low supersaturation, the β form exhibited needle-shaped habit which is the shape generally reported [1]. However at high supersaturation, β crystals showed surprising lozenge slab habit close to that of α form (figure 1 a). These lozenge slabs were confirmed to be the β polymorph by X-ray Diffraction. Therefore, relying only on the appearance to differentiate between the two LGlu polymorphs can be misleading. In stagnant conditions, spontaneous nucleation of LGlu could not be observed at similar low supersaturation as in the stirred vessel within 72 hours. At high supersaturation only the polymorph β nucleated as lozenge slabs (Figure 1b) and grew with the same shape or transformed to hexagonal slabs depending on the supersaturation. These results will be used to model the competition between nucleation and growth of the two polymorphic phases.
Figure 1. (a) Images of LGlu polymorphs in stirred conditions: (1) α form,(2) β form with lozenge shape (3) β form with needle shape. (b) Microscope image of β polymorph with lozenge shape in stagnant conditions
References: [1] Kitamura, M. (1989). Polymorphism in the crystallization of L-glutamic acid. Journal of crystal growth, 96(3), 541-546. [2] Bernstein, J. (2007). Polymorphism in molecular crystals (Vol. 14). Oxford University Press, chapter1.
Design of Optimal Start-up Procedures for MSMPR Crystallizers Kamaraju Vamsi Krishna*1, Power Graham1, Hou Guangyang2, Zhao Yan1, Glennon Brian1
1Synthesis and Solid State Pharmaceutical Centre (SSPC), Department of Chemical and Bioprocess Engineering, University College Dublin, Belfield, Dublin 4, Ireland
2APC Ltd, Belfield Innovation Park, Dublin 4, Ireland *email: [email protected] With increasing interest on continuous processing in pharmaceutical manufacturing due to its distinct advantages over batch operation in terms of delivering consistent product, safety, and increased productivity, Mixed Suspension Mixed Product Removal (MSMPR) crystallizers are widely employed for continuous crystallization of active pharmaceutical ingredients (APIs). However, design of optimal start-up procedures for MSMPR is not sufficiently addressed in the literature yet, which can critically affect the economic operation of continuous crystallization processes.[1] Few attempts have been made in the past to understand the effect of various process conditions on the settling time to reach steady state. Hou et al. (2014) experimentally studied the impact of various seed distributions and concluded that seeding with previously isolated MSMPR product suspension shows the shortest settling time.[2] Su et al (2015) developed rigorous mathematical models to demonstrate the application of concentration control strategy for start-up procedure of single stage and cascaded MSMPR antisolvent crystallizers.[3] Further, Yang and Nagy (2015) have recently studied the start-up optimization methods for combined cooling and antisolvent MSMPR crystallizer by choosing optimal trajectories to achieve minimum start-up duration and amount of waste.[4] The current study presents a systematic methodology for designing optimal start-up procedure using the advantages of batch crystallization. The effect of different initial suspension properties on the settling time for steady state is studied with the help of dynamic simulations based on population balance modeling of MSMPR crystallizers. Thus, batch control strategies were employed to achieve the target suspension properties required to minimize the amount of out-of-spec MSMPR product. Experimental validation confirms the advantage of the proposed methodology compared to general start-up.
(a) (b) Figure 1. Dynamic simulations of MSMPR with different initial suspensions – (a) Concentration profiles; (b) Profiles of volume-weighted mean size of product crystals References 1. Myerson, A.S., et al., Journal of Pharmaceutical Sciences, 2015. 104(3): p. 832-839. 2. Hou, G.Y., et al., Crystal Growth & Design, 2014. 14(4): p. 1782-1793. 3. Su, Q., Z.K. Nagy, and C.D. Rielly, Chemical Engineering and Processing: Process Intensification, 2015. 89(0): p. 41-53. 4. Yang, Y. and Z.K. Nagy, Industrial & Engineering Chemistry Research, 2015.
A phenytoin polymorph accessible via surface mediation Daniela Reischl,1 Christian Röthel,1,2 Eva Roblegg,1 Heike M.A. Ehmann3 and Oliver Werzer1*
1 University of Graz, Institute Pharmaceutical Sciences, Department for Pharmaceutical Technology, 8010 Graz, Austria 2Graz University of Technology, Institute for Solid State Physics, 8010 Graz, Austria 3Graz University of Technology, Institute for Chemistry and Technology of Materials, 8010 Graz, Austria
*email: [email protected]
The exploration for new polymorphic forms of organic compounds is one of the most effective route for controlled manipulation of drug release from solid dosage forms. In recent years extensive and theoretical work was applied to identify and predict new polymorphs, especially those useful for pharmaceutical applications. In general, changes in parameters like choice of solvent, concentration, temperature and pressure are capable of changing the polymorphic assembling as another local energetic minimum is accessible. Another route for a polymorphic alteration is crystallization in close vicinity of surfaces. Such crystallization often reveals the formation of new polymorphs which are only existent some monolayers off a solid surface and are therefore classified as surface induced or surface mediated.[1][2] Furthermore, there is evidence that some of these surface mediated phases result from growth kinetics rather than certain thermodynamic parameters.[2] In this work, we demonstrate the formation of a new surface mediated polymorph of phenytoin, a drug molecule, in a model experiments. So far, experiments were only able to resolve one polymorph of phenytoin either on in the bulk or on surfaces.[3][4] Anyway, by the usage of simple, but very effective techniques like controlled drop casting, spin coating or vacuum deposition the formation of a new surface mediated polymorph is demonstrated at conventional silica surfaces. As will be shown, this phase is only accessible in thin films thus sophisticated experimental techniques like atomic force microscope as well as gracing incidence x-ray diffraction are required to gain information on this new polymorph within thin films. The results reveal a morphology which is distinct from those of the bulk phase.[3][4] Furthermore the unit cell of the surface mediated phase is extended compared to this of the bulk phase meaning a less dense packing is present in the surface mediated phase. This typically means that the stability of the surface mediated phase is also reduced, which is further supported by in-situ temperature dependent measurements; a monotropic solid-solid phase transition into the bulk phase takes place at around 160°C. As an application relevant consequence, this surface phase has a significantly better dissolution behavior compared to phenytoin in its bulk polymorph with the release into the dissolution media being much faster. The results presented show a very promising approach for drug dissolution enhancement which might be directly accessible within application like transdermal patches or buccal stripes. For an application in conventional solid oral dosage forms, some additional work is required to generate this polymorph onto nanoparticles or materials suitable for powder processing which should be accessible with the pre-knowledge from this study. .
References: [1] D. Nabok, et. al. Physical Review B 12 (2007) 235322. [2] B. Wedl, et. al. RSC Advances 01 (2012) 4404 [3] H. M.A. Ehmann, et. al. J Phys Chem C 118 (2014) 12855 [4] H. M.A. Ehmann, et. al. Cryst. Growth Des. 15 (2015) 326
Nucleation Kinects of Co-crystal by Simultaneous Monitoring of Dissolution and Crystallisation using Process Raman Technique: Precipitation of Burkeite Boyang. Zou1*, Xiaojun Lai1, Dan Xu2 and Luis Martin de Juan2 1Institute of Particle Science and Engineering, School of Chemical and process Engineering, University of Leeds, Leeds, LS2 9JT, United Kingdom
2 Procter & Gamble, Newcastle Innovation Centre, Newcastle, United Kingdom *email:[email protected] The formation of co-crystal or double salt is attracting interest of research due to its important applications in enhancing physical and chemical properties of final products of crystalline materials, such as stability, solubility, compressibility and hygroscopicity.[1] Burkeite is an inorganic co-crystal with a wide range of applications, e.g. it is an essential component of personal care products. Industrial processes precipitate burkeite isothermally from the solution system while raw material particles of Na2SO4 and Na2CO3 are dissolving This makes the crystallisation kinetics study using conventional measurement of induction time infeasible, due to the co-existence of multiple component particles in the system and the varying degree of supersaturation prior to burkeite precipitation. Therefore, the solution equilibrium and crystallisation kinetics are difficult to control during the process. This research employed in-situ Raman technique, with the aid of Chemometrics, to determine the concentrations of multiple components in their different phases simultaneously as well as to detect the onset of burkeite precipitation. A new methodology has been developed for fast determination of detailed isothermal ternary phase diagram of Na2CO3-H2O-Na2SO4 system (e.g. see Figure 1). The modified KBHR[1,2] approach for nucleation kinetics determination was applied to this isothermal crystallisation system. The detected metastable zone limits with respect to the phase equilibrium were correlated to the increase rate of supersaturation during the dissolution of Na2SO4. Using this first principle model, the nucleation mechanism, interfacial tension and critical size of burkeite nucleus were derived. This novel strategy could be applied to other systems, offering a fundamental base for modelling nucleation rate and size control for industrial process of co-crystals.
Figure 1. A Na2CO3-H2O-Na2SO4 ternary phase diagram determined by using in-situ Raman technique References: [1] Ainouz, A., Authelin, J.R., et al., Int. J. Pharm. 2009. 374, 82-89. [2] D.M.C. Corzo, A. Borissova, et al., Cryst.Eng.Comm., 2014, 16, 974
Continuous production of lactose monohydrate crystal seed suspensions by rapid antisolvent crystallization using a continuous nucleation unit
Pól MacFhionnghaile*, John McGinty, Jan Sefcik
EPSRC Centre for Innovative Manufacturing in Continuous Manufacturing and Crystallisation, Department of Chemical and Process Engineering, University of Strathclyde, G1 1XJ, Glasgow, UK [email protected]
A novel continuous nucleation unit was used to produce seed crystals of lactose monohydrate via rapid antisolvent crystallization. We compared several different solvent-antisolvent systems with varying solvent mixture compositions. In this study isopropanol, ethanol, and acetone were used as antisolvents and were continuously mixed with aqueous lactose solutions in a concentric static mixer setup at a constant temperature. Due to the design of the nucleator it was possible to observe the solvent-antisolvent mixing region while being able to vary the flow rates of the inlet streams and through that varying solvent mixture composition and the overall process flow rate. The fully mixed solutions were feed into a temperature controlled monitoring vessel for on-line analysis using FTIR spectroscopy, FBRM and PVM. It was found that by changing key process parameters, such as flow rate and solvent- antisolvent composition, resulting particle attributes of lactose seed crystal suspensions could be controlled providing seeds of a desired solid form, particle size and morphology. This approach can be used to generate seed suspensions in reproducible and scalable manner for seeding of either batch or continuous crystallization processes.
On‐line monitoring: Temp., Particle Size Monitoring (FBRM), Solvent V1 Vessel compostion (FTIR), Morphology (PVM) Lactose Mixing Pump 1 Solution Observable through glass vessel Pump 3
Off‐line monitoring: V2 Crystallinity (PXRD), Spectroscopy (ATR‐IR), V3 Particle size and shape Antisolvent Pump 2 (Microscopy, Malvern) Collection Vessel
Figure 1. Schematic diagram of the nucleation set-up
POSTER
S03-P03 Achiral molecules in engineering of non-centrosymmetric crystal structures: polymorphs and co-crystals of 1H-3,5-dinitropyridine-2-one
Fedyanin Ivan* and Lyssenko Konstantin
A.N.Nesmeyanov Institute of Organoelement Compounds of Russian Academy of Sciences, Vavilova st. 28, 119991, Moscow, Russian Federation *email: [email protected]
Organic molecules that have no chiral center tend to crystallize in centrosymmetric space groups, as this type of packing minimizes the energy of interactions between bond dipoles. Crystal structure of 1H-3,5-dinitropyridine-2-one (DNHQ) is non-centrosymmetric, in contrast to its close analogues (e.g. thymine and uracil, space group P21/c). Instead of more common centrosymmetric dimers, chiral H-bonded chains are the main element of supramolecular organization in DNHQ. These chains also found in the new polymorph of DNHQ, which has two symmetrically independent molecules assembled into these chains. Note that in series of co-crystals of DNHQ with polyaromatic hydrocarbons crystal structures are all non-centrosymmetric. The chiral chain is therefore the supramolecular synthon that defines the arrangement of DNHQ molecules in its crystals. The hydrogen bond in polymorphs and co-crystals of DNHQ is bifurcate, but parameters of the second interaction with oxygen atom of nitro group vary significantly among crystal structures, as well as properties of weaker stacking and non-specific interactions. High-resolution X-ray diffraction experiments and ab-initio calculations of crystals and isolated molecular complexes allowed clarifying the nature of intermolecular interactions, estimate their energy and overall stability of crystal packing. We propose the possible reasons for non- centrosymmetricity of the structures, and a model for crystallization of the second DNHQ polymorph that can be only obtained by heteronucleation.
Figure 1. Deformation electron density distribution for intermolecular H-bond in the co-crystal of DNHQ with phenanthrene.
This study was supported by Russian Foundation for Basic Research, Project No. 14-03-010894
S03-P05 Non-Photochemical LASER-Induced Nucleation in Water/Ethanol of sulfathiazole. Li Wenjing1,2, Aziza Ikni1,2, Philippe Scouflaire1,3, Shi Xiaoxuan1,2, Nouha El Hassan1,2, Jean- Michel Gillet1,2, Anne Spasojević-de Biré1,2* 1 Université Paris Saclay, CentraleSupélec, Campus de Châtenay, Grande Voie des Vignes, 92295 Châtenay-Malabry, France 2 CNRS, UMR 8580, Laboratory “Structures Propriétés et Modélisation des Solides” (SPMS), Grande Voie des Vignes, 92295 Châtenay-Malabry, France 3CNRS, UPR 288, Laboratory “Energétique Moléculaire et Macroscopique, Combustion” (EM2C), Grande Voie des Vignes, 92295 Châtenay-Malabry, France
Crystallization is a crucial in the pharmaceutical industry, due to its importance in the control of the crystal purity, shape, size distribution and polymorphism, which can affect directly the drug stability, dissolution and bio-availability. It becomes more and more significant to find an efficient way to control the crystallization. The non-photochemical laser induced nucleation (NPLIN)1, 2 shows great advantage as an unusual nucleation method in controlling temporarily and sometimes spatially the crystallization by manipulating the laser parameters. In order to demonstrate experimentally the feasibility of NPLIN applied in pharmaceutical molecules, experiments were realized with solutions of sulfathiazole dissolved in water/ethanol (1:1). Firstly, the solubility curve and metastable zone were measured for the sulfathiazole solutions, it turns out βc, 25, w/e (168hrs) = 170%. NPLIN succeeded in inducing nucleation of the metastable solutions within several minutes, the crystal nucleus appears in the interface air/solution. It is found that there is a dependency of the nucleation efficiency on laser power density and also on supersaturation β of the sulfathiazole solutions (figure 1a). Furthermore, the experiments implied the number of laser shots effected directly the obtained crystal number and size, the more laser shots sent to irradiate the solution, the more crystals were produced and the smaller the crystal size was (figure 1b). Moreover, after characterization of the obtained crystals by single crystal diffractometer and by Raman diffusion, it is noticed that the linear polarization favored the formation of polymorph IV, while the circular polarization tended to increase the proportion of the polymorph III. To study the interaction energy of the sulfathiazole molecule with each neighbor molecule, a full DFT computation was carried out using the same quantum chemistry model within the functional density theory framework (M06-2X/cc-PVTZ), available from the Gaussian09 software. This theoretical calculation reveals, when the form III grows in the direction of the most stable dimer, it will form a two dimensional crystal packing; while form IV will form a one dimensional crystal packing. This result confirms the hypothesis that the linear polarization favors the production of form IV while the circular polarization favors the formation of form III.
0,5 CBZ-Acetonitrille-CP )
2 CBZ-Acetonitrille-LP CBZ-Methanol-CP 0,4 CBZ-Methanol-LP Sulfathiazole-W/E-CP Sulfathiazole-W/E-LP 0,3
0,2
0,1 Laser power density (GW/cm density power Laser 0,0 105 110 115 120 125 130 135 140 Supersaturation (%) a) b) 1. CLAIR B., IKNI A., LI W, SCOUFLAIRE P., QUEMENER V. SPASOJEVIĆ - de BIRÉ A. « A new experimental setup for a high throughput controlled Non-Photochemical LASER-Induced Nucleation (NPLIN). Application to Glycine crystallization» J. Appl. Crystallogr. 2014, 47, 1252-1260 2 IKNI A., CLAIR B., SCOUFLAIRE P., VEESLER S., GILLET J-M., EL HASSAN N., DUMAS F., SPASOJEVIĆ - de BIRÉ A. «Experimental demonstration of the carbamazepine crystallization from Non-Photochemical LASER- Induced Nucleation in acetonitrile and methanol » Cryst. Growth & Design, 2014, 14(7) 3286-3299
S03-P06 Purification of fermentatively produced specialty carbohydrates
Bekers Katelijne Maaike*, Moens Helena, Vanlerberghe Brecht, Waegeman Hendrik
Bio Base Europe Pilot Plant, Rodenhuizekaai 1, Gent (Belgium) *email: [email protected]
Specialty carbohydrates are of high interest for industrial applications. Because of their role in human biology, many areas could benefit from their multiple health benefits. Especially cosmetic, pharmaceutical and nutraceutical markets have high potential. However, the production of specialty carbohydrates for industrial use by chemical synthesis is unsuitable. The developed processes have major issues with stereoselectivity, complex and expensive techniques for purification and the use of toxic compounds. Production is therefore not economic viable and especially for nutraceutical applications the use of toxic compounds is unwanted or even prohibited. Enzymatic synthesis has the benefit of using more specific reactions and less harsh conditions, but still the complexity of the molecules and purification remain a tremendous hurdle to tackle. Because of these issues, biotechnological routes to produce specialty carbohydrates are currently developed. Whole cells have been metabolically engineered to produce different monosaccharides or oligosaccharides of interest, starting from a supplied precursor. The cells are engineered as such that metabolic pathways involved in the degradation of the precursor are eliminated and the production of by-products strongly reduced. By doing so, the precursors are efficiently and directly converted into the desired product. By using a fermentation process, a cost and time effective process can accordingly be developed, allowing an interesting economy of scale with industrial compatible cost and yield for different specialty carbohydrate targets. Bio Base Europe Pilot Plant (BBEPP) is involved in the optimization and scale-up of the fermentation process and downstream processing of the production of specialty carbohydrate. One of the issues in their process development that is currently addressed by BBEPP, is the underdeveloped downstream process (DSP). The process economics would benefit significantly if a crystallization process could be applied. This poster presentation will give an overview of different strategies applied and the equipment used by BBEPP for development, scale-up and demonstration of product recovery and purification. With this, it will discuss the opportunities and challenges in applying crystallization for the product recovery and purification of monosaccharides an oligosaccharides from fermentation broth.
S03-P12 Crystallisation Characteristics of an Organic Material in Industrial Mother Liquor with Impurities
Khan Shahid 1, Mahmud Tariq*1, Roberts Kevin 1, Zhu Xiaofeng 1, George Neil2 and Sillers Pauline2
1Institute of Particle Science and Engineering, School of Chemical and Process Engineering, The University of Leeds, Leeds LS2 9JT, UK 2Syngenta, Jealott's Hill International Research Centre, Bracknell, Berkshire RG42 6EY, UK
In pharmaceutical and fine chemical industries, the isolation and purification of organic materials are commonly carried out using various solution crystallisation techniques including the batch cooling crystallisation process. In industrial crystallisation processes, mother liquors usually contain unwanted dissolved molecules (generally referred to as impurities) produced via reaction steps prior to the crystallisation and their concentration may vary from batch to batch. It has long been established that the supersaturation driven nucleation and crystal growth rates can change profoundly even in the presence of low levels of impurities added intentionally to or inherently present in the solution, and thus affects the size, shape and purity of the product crystals. This could also impede efficient downstream processing of crystals such as filtration, drying and milling. In order to control industrial crystallisation processes to meet product specifications, such as narrow crystal size distribution, high chemical purity and desired crystal morphology, with high product yields, it is important to develop a detailed understanding of the crystallisation characteristics of product materials in the mother liquors containing process generated impurities. This can be achieved via replicating the industrial process at laboratory scales in the presence of impurities. The work reported here investigated the crystallisation behaviour of an organic material (referred to as compound A due to confidentiality) from an industrial mother liquor (which mainly contains an organic compound), corresponding pure solvent and the pure solvent doped with the process generated impurity as a function of representative processing variables, e.g., level of impurities, seeding and cooling profile. Experiments were carried out in a 500 mL jacketed glass stirred tank crystalliser with temperature controlled using Julabo FP50-HD thermostatic bath. The metastable zone width and induction time for the nucleation of compound A were determined using a turbidimetric method as a function of both cooling rate and solute concentration in the pure and in impurity added solvent. ATR-FTIR spectroscopy coupled with a PLS calibration model was used for on-line monitoring and control of supersaturation during the batch cooling crystallisation of compound A. The metastable zone width was found to be wider in the mother liquor and in the solvent doped with impurity compared with that in pure solvent. The induction time for nucleation of compound A increases with increasing impurity concentration. A significant outcome of this research is reflected in the observations that the crystals produced in pure solvent have a much different physical form compared to those crystallised from mother liquor. The former crystals tend to be smaller and heavily agglomerated when compared to the latter which display superior crystal quality and external morphology. The latter perhaps is a reflection of the nucleation and solubilisation abilities of the other components present in the mother liquor. However, in the pure system, particles spontaneously nucleated at much higher supersaturation levels leading perhaps to an excessive primary nucleation rate resulting in smaller and more agglomerated crystals.
SESSION 4 Bulk Crystal Growt
A new large-lattice-constant perovskite substrate crystal
Uecker, Reinhard*1, Klimm, Detlef1, Bertram, Rainer1, Guguschev, Christo1, Brützam, Mario1, Kwasniewski, Albert1, Klupsch, Michael1, Gesing, Th.M.2, Schlom, D.G.3
1Leibniz Institute for Crystal Growth, Max-Born-Str. 2, D-12489 Berlin (Germany) 2University of Bremen, Solid State Chemical Crystallography /FB02, Leobener Str. /NW2, D-28359 Bremen (Germany) 3Department of Materials Science and Engineering, Cornell University, 230 Bard Hall, Ithaca, NY 14853-1501 (USA) *email: [email protected]
A broad range of bulk oxide crystals with cubic and pseudo cubic perovskite structure is used as substrates for the epitaxy of high quality perovskite thin films with targeted strain. Such strain engineering allows the enhancement or total change of the properties of functional oxides. LuAlO3 has the smallest lattice constants of the commercially available oxide perovskites (3.67 Å) whereas the discovery of new thin films continuously requires new substrates with larger lattice constants. For several decades the universal SrTiO3 has been that employable perovskite-type substrate with the largest lattice constant (3.90 Å). First the introduction of the rare earth scandates LnScO3 (Ln=Dy-La) shifted the upper limit to 3.95-4.05 Å. However, with CeScO3 and LaScO3 the largest of them are excluded from Czochralski growth -the most appropriate method for the growth of high perfection bulk crystals- because of their exceptional high melting temperature (>2250 °C). Therefore, PrScO3 with 4.02 Å forms the end of this range. I.e., the large number of 17 different substrates covers a lattice constant range of 0.35 Å (3.67-4.02 Å). This dense occupation enables a very precise tuning of film properties in this region by strain engineering. Notwithstanding that several oxide perovskites having larger lattice constants are reported, so far only one could be grown as bulk crystal: LaLuO3 (4.17 Å). That means there is a serious lack of larger-lattice-constant perovskites to be used as substrate crystals for advanced new thin films. To discover new perovskites in this region which can be grown as bulk crystal, the pseudo binary phase diagram of the above edge components LaScO3-LaLuO3 was systematically investigated. In the result solid solution formation was found close to the 1:1 composition. The liquidus temperature is below 2200 °C which allows the growth by the Czochralski method from an iridium crucible. This solid solution exhibits an interesting structure: Because the Lu ion can occupy both, the position of the large A cation and that of the smaller B cation in the perovskite cell, a few percent of it were proven to occupy besides B also a few A sites. Thus the formula of the Czochralski grown bulk crystal is (La1.94,Lu0.06)(Lu1.11Sc0.89)O6. It shows a pseudo cubic lattice constant of about 4.12 Å, i.e., it fits exactly into the gap between PrScO3 and LaLuO3. Because of the low segregation, the shift of the lattice constants over the crystal length is rather small. Therewith, for the first time an excellent substrate crystal for highly topical films like BaSnO3 (transparent semiconducting oxide), BiScO3 (piezoelectric with high temperature stability) and PbZrO3 (interesting antiferroelectric) could be made available.
Floating-zone Growth of Large Single-Crystal of Haldane Chain Compound SrNi2V2O8
A.T.M. Nazmul Islam*1, B. Lake1, A.K. Bera1, B. Klemke1, E. Faulhaber2, J.M. Law3, A. Schneidewind4, J.T. Park5, E. Wheeler6
1Helmholtz-Zentrum Berlin für Materialien und Energie, D-14109 Berlin (Germany) 2Helmholtz-Zentrum Berlin für Materialien und Energie, Gemeinsame Froschergruppe, D-85747 Garching (Germany) 3Hochfeld Magnetlab Dresden, Helmholtz-Zentrum Dresden-Rossendorf, D-01314 Dresden (Germany) 4Jülich Center for Neutron Science JCNS, Froschungszentrum Jülich GmbH, Outstation at MLZ, D-85747 Garching (Germany) 5Heinz Maier-Leibnitz Zentrum, TU München, D-85747 Garching (Germany) 6Institut Laue-Langevin, Boite Postale 156, 38042 Grenoble Cedex (France) *[email protected]
Low dimensional quantum magnets are a special class of material sought by condensed matter physicists, since they show exotic magnetic behaviors. Haldane in his pioneering work predicted that one-dimensional (1D) Heisenberg antiferromagnet systems with integer spin will show a singlet ground state and a gapped excited state known as the Haldane gap, whereas half-integer spin chains will have a spin-liquid ground state with gapless spinon excitations. ANi2V2O8 (A=Pb, Sr) whose structure has magnetic Ni2+ ions with spin S=1 arranged in a screw chain along the c-axis forming a quasi 1D spin-chain structure, is an ideal candidate to study the integer spin Haldane chain. These materials provide fertile ground to investigate the effect of the inter-chain interactions and single ion anisotropy on the Haldane state. In addition they can be tuned through a quantum phase transition to long-range magnetic order via application of a magnetic field. Large and high quality single crystals of these compounds are essential for such studies. However, ANi2V2O8 (A=Pb, Sr), is a incongruently melting compound of three oxides AO (A=Sr,Pb), NiO and V2O5 among which the phase relationship is not well understood. So, despite continual interest, more than a decade after the discovery of ANi2V2O8 (A=Pb, Sr), there is no report on single-crystal growth of either compound. We think the challenge lies in finding a suitable flux composition for growth of such a complex multinary compound. In this work we report the first growth and characterization of a large single crystal (~25mm in length and ~5 mm in diameter) of SrNi2V2O8 by Traveling solvent floating zone method in an IR heated Floating-zone furnace.
Europium and potassium co-doped strontium metaborate single crystals grown by the Czochralski method
Głowacki Michał 1*, Solarz Piotr 2, Ryba-Romanowski Witold 2, Martín Inocencio R. 3, Diduszko Ryszard 1,4, Berkowski Marek 1
1 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland) 2 Institute of Low Temperature and Structure Research, Polish Academy of Sciences, ul. Okólna 2, 50-950 Wrocław (Poland) 3 Departamento de Física, Instituto de Materiales y Nanotecnología (IMN),Universidad de La Laguna, Av. Astrofísico Francisco Sánchez, s/n E-38206 La Laguna, Tenerife (Spain) 4 Tele and Radio Research Institute, Ratuszowa 11, 03-450 Warsaw Poland *e mail: [email protected]
Strontium borates are suitable materials for use as matrices for luminescent dopant ions. Several published reports have been devoted to doping strontium metaborates with europium [1-2], but the results were inconsistent. To elucidate the ambiguity of available information we undertook attempts to grow good quality SrB2O4 single crystals and investigate the light emission from both Eu2+ and Eu3+ ions that occur in this host. Divalent europium ions give rise to an UV–blue luminescence, while the trivalent ones– to a red luminescence. As a consequence the materials under study are promising phosphors for white light emission applications. Recent studies on europium doped strontium borates [3] have shown that the europium emission is more efficient when the host matrix is co-doped with alkali ions. In this presentation we report on the first successful growth of strontium metaborate single crystals co-doped with europium and potassium by the Czochralski method and on their structural and spectroscopic features. In particular, results of optical gain measurements using pump and probe method will be presented and discussed. a) b)
Figure 1. As-grown SrB2O4 single crystals (a) and their diffraction patterns (b) Acknowledgements: The work was funded by the Polish National Science Center (NCN) on the basis of the decision number DEC-2013/09/D/ST5/03878
References: [1] K. Machida, G. Adachi, J. Shiokawa, M. Shimada, M. Koizumi, J. Lumin. 21 (1980) 233-237 [2] H. J. Seo, B. K. Moon, B. J. Kim, J. B. Kim, J. Phys: Condens Matter 11 (1999) 7635-7643 [3] Hua-Yu Zhu, Yin-Wen Li, Li Zhang, Shou-Li Suo, Al-De Sun, Man-Geng Lu, Optoelectr. Adv. Materials 6 (2012) 555-559
3+ Flux growth and characterization of highly Yb -substituted cubic RE2O3 (RE=Gd, Y, Lu) laser crystals and of cubic Lu1.56Gd0.41Eu0.03O3 crystals
Matias Velázquez*1, Philippe Veber1, Gabriel Buşe1, Yannick Petit1, Philippe Goldner2, Olivier Plantevin3, Daniel Rytz4, Emmanuel Véron5, Rekia Belhoucif6, Véronique Jubera1, Patrick Aschehough2, Gérard Aka2
1CNRS, Université de Bordeaux, ICMCB, UPR 9048, 87 avenue du Dr. A. Schweitzer, 33608 Pessac cedex (France) 2PSL Research University, Chimie ParisTech – CNRS, Institut de Recherche de Chimie Paris, 75005 Paris (France) 3CSNSM, UMR 8609 CNRS-Université d’Orsay, Bât. 108, 91405 Orsay Campus (France) 4FEE-GmbH, Struthstrasse 2, 55743 Idar-Oberstein (Germany) 5CEMHTI-CNRS UPR 3079, 1D Av. de la Recherche Scientifique, 45071 Orléans (France) 6Faculté de Physique, Laboratoire d’Électronique Quantique, USTHB, BP 32 El alia, 16111 Bab Ezzouar, Alger (Algeria) *email: [email protected]
Developing large optical grade cubic rare-earth sesquioxides (RE2O3, RE=Sc, Y, Gd, Tb, Lu) single crystals, pure or doped with Yb3+ ions stands as one of the most challenging endeavours of today’s crystal growth [1]. This is essentially due to the high melting point of these compounds (~2400-2500°C) and because of a series of structural phase transitions occurring upon cooling for 3+ some of them, as Gd2O3 or Tb2O3. In this work, we will present highly Yb -substituted Gd2O3, Y2O3 and Lu2O3 single crystals of the cubic phase with dimensions of several mm³ which were recently grown by a newly designed high-temperature solution growth method [2,3]. Furthermore, we will report on their characterization by means of X-ray diffraction, visible, near infrared and Fourier transformed infrared (FTIR) spectroscopy, electron probe microanalysis (EPMA) coupled with wavelength dispersive spectroscopy (WDS), exhaustive and complete chemical analysis by GDMS, emission spectroscopy and Squid magnetometry. Our solution growth method uses an original and nontoxic solvent with a growth setup operating in air between 1250°C and 1100°C, that is, at half the melting temperature of rare-earth sesquioxides. The high-temperature solution growth conditions and two thermodynamic features of the solvent will be discussed. Indeed, not only cubic 3+ Gd2O3 single crystals had never been grown before, but Yb -substitution levels as high as Gd1.61Yb0.39O3, Y1.69Yb0.31O3 and Lu1.86Yb0.14O3 were remarkably reached. In addition to demonstrating that this flux growth process allows the obtention of optimal doping for high-power laser applications, we will emphasize that it impedes the dissolution of OH- groups in the crystals, avoids the reduction of Yb3+ ions into Yb2+ without resorting to any post-growth thermal annealing, hinders the Yb-pairs formation kinetics in Y2O3 crystals and, last but not least, favours broader absorption and emission bands. Laser operations were demonstrated with uncoated and uncooled 3+ 3 Yb -doped cubic Gd2O3 and Y2O3 crystals [4]. We will also show and discuss our latest ~0.5 cm cubic Lu1.56Gd0.41Eu0.03O3 scintillator crystal, the crystal habit and physical properties of which were fully characterized by Laue X-ray diffraction, absorption and emission spectroscopies and magnetic susceptibility measurements.
References: [1] A. Yoshikawa, V. Chani, MRS Bulletin, 34 (2009) 266. [2] Ph. Veber, M. Velázquez, V. Jubera, S. Pechev, O. Viraphong, Cryst. Eng. Comm. 13 (16) (2011) 5220-5225. [3] M. Velázquez, Ph. Veber, G. Buşe, Y. Petit, Ph. Goldner, V. Jubera, D. Rytz, A. Jaffres, M. Peltz, V. Wesemann, P. Aschehough, G. Aka, Opt. Mater., 39 (2015) 258-264. [4] F. Druon, M. Velázquez, P. Veber, S. Janicot, O. Viraphong, G. Buşe, M. Abdou Ahmed, T. Graf, D. Rytz, P. Georges, Opt. Lett., 38(20) (2013) 4146–4149.
On the crystal growth of incongruent borate type crystal LaxGdyScz(BO3)4 (x + y + z = 4) by the Czochralski method
Lucian Gheorghe1, Flavius Voicu1, Gabriela Salamu1, Federico Khaled2, Alexandru Achim1, Cristina Gheorghe1, Pascal Loiseau2, Nicolaie Pavel1, Gérard Aka2
1 National Institute for Laser, Plasma and Radiation Physics - LSSQE, Magurele-Bucharest, Romania 2PSL Research University, Chimie ParisTech – CNRS, Institut de Recherche de Chimie Paris, 75005 Paris, France *email: [email protected]
Some of the most important NLO crystals that are used in current commercial applications include KTiOPO4 (KTP), KH2PO4 (KDP), KD2PO4 (DKDP), β-BaB2O4 (BBO), YAl3(BO3)4 (YAB), LiB3O5 (LBO) and periodically poled LiNbO3 (PPLN). Despite of the wider usage, essentially all of these crystals melt incongruently with the exception of LiNbO3, so they all have to be grown by flux method, which makes them expensive and limited in size most often. So, the feasibility to produce large NLO crystals at low cost is highly desirable, especially for high-power or high-energy frequency conversion applications. LnSc3(BO3)4 (Ln = lanthanide) borates crystallizes in different allotropic forms depending on the ratio of the ionic radii of Ln and Sc (rLn/rSc). For example, for Ln = La, LaSc3(BO3)4 - LSB crystal is centrosymmetric (monoclinic structure, space group C2/c) and therefore optically linear, while for Ln = Gd, GdSc3(BO3)4 - GSB crystal is isostructural with non-centrosymmetric trigonal huntite mineral CaMg3(CO3)4 (space group R32) and consequently optically nonlinear [1]. Recently it was demonstrated that the monoclinic structure of LSB can be converted to the trigonal form by 3+ doping with smaller Gd ions, and LaxGdyScz(BO3)4 (x + y + z = 4) - LGSB nonlinear crystals were grown by the top seeded solution growth method (TSSG) from a flux of Li6B4O9-LiF [2]. Even though LSB present a non-congruent melting behaviour, it can be grown by the Czochralski method if the starting material contains an excess of LaBO3. Therefore an attempt of growing good quality and large size crystals of LGSB by the Czochralski method was undertaken. Also, the doping with luminescent ions was investigated for self-frequency doubling applications. XRD and DTA analysis were performed in order to determine both the limits of the solid solution of LaxGd1-xSc3(BO3)4 with space group R32 and the most efficient composition of the flux. The crystal growth parameters were then optimized and relatively large size (about 10 mm in diameter and 30 mm in length) crystals of LGSB and Yb:LGSB of high quality were grown by the Czochralski method for the first time (Fig. 1). The optical properties of the grown crystals were evaluated and the spectroscopic and infrared laser emission properties of Yb:LGSB crystals were characterized. All these features suggest that pure and Yb-doped LGSB crystals have great potential for high-power NLO applications.
Figure 1. The photographs of LGSB (left) and Yb: LGSB (right) grown crystals.
References [1] S. T. Durmanov, O. V. Kuzmin, G. M. Kuzmicheva, S. A. Kutovoi et al., Opt. Mater., 18 (2001) 243. [2] Xiang Xu, Ning Ye, J. Cryst. Growth, 324 (2011) 304.
Improvement of crystal growth of Li4SiO4 single crystals for neutron detection and their scintillation and luminescence properties
Jan Pejchal*1, Vladimir Babin1, Alena Beitlerova1, Shunsuke Kurosawa2,3, Yuui Yokota2,3, Akira Yoshikawa2,3, Martin Nikl1
1Institute of Physics CAS , Cukrovarnicka 10, Prague 6 (Czech Republic) 2Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai (Japan) 3New Industry Creation Hatchery Center, 6-6-10 Aoba, Aramaki, Sendai (Japan) *email: [email protected]
Neutrons have recently become essential probes in material research on both macroscopic and microscopic scale. They can be applied in various imaging techniques or scattering techniques to investigate material or molecular structure and others [1]. Possible applications in security systems or oil well logging can be considered as well. We have investigated Li4SiO4 scintillation crystals for their possible application in neutron detection due to high Li content, which would enable a sufficient probability of interaction of the material with a neutron, and low density of 2.35g/cm3, which is important for lowering the background gamma-ray sensitivity. Its lower melting point (1250 °C) might enable incorporation of Ti3+ without being oxidized to Ti4+. Then, the Ti3+ 3d-3d luminescence in red spectral region, which matches the sensitivity of contemporary photodiodes, might be exploited. The micro-pulling-down method [2,3] employing the Ir crucible and afterheater was optimized for crystal growth of Li4SiO4 taking into account the incongruent Li evaporation. Moreover, it was found that increased heating power led to milder temperature gradient, thicker meniscus, smaller crystal diameter and resulting smaller tension in the as-grown crystals. This allowed us to grow high-quality crack-free single crystals. The undoped, Ti-, Cr-, Mn- and Al- doped crystals were prepared and studied. Preliminary radioluminescence measurements under X-ray excitation showed quite high overall scintillation efficiency of the Ti-doped sample reaching as high as 250% of that of Bi4Ge3O12 reference scintillator. The emission spectrum was dominated by one broad band peaking at 350 nm, tentatively ascribed to Ti4+ charge transfer luminescence. Reasonable light yield of 10000 photons/neutron was found. However, its long decay time of 54 μs might be a limitation especially for high counting rate applications. The overall scintillation efficiency of the Cr3+ sample was much lower and the spectrum shows one broad peak at 463 nm with a decay time around 10 μs, which are characteristics not corresponding to those of Cr3+ ion. This means that another luminescence process takes place. The efficiency of the Mn-doped sample was slightly higher and the spectrum consisted of two broad bands at 442 nm and 680 nm. The latter one was characterized by a long decay time of 5 ms which would correspond to the Mn4+ luminescence. The origin of the 442 nm one with much faster decay in the order of microseconds is not clear. On the other hand, the radioluminescence spectrum of the Al-doped sample closely resembled to that of the Ti-doped one, just its magnitude is considerably lower. The similarity of the temperature dependences of photoluminescence spectra and decay time for these two samples might suggest that Ti might be stabilized still as a trivalent ion and an unusual luminescence mechanism might take place for the trivalent dopants. Peculiarities and optimization of crystal growth and a preliminary sketch of luminescence mechanism and dopant incorporation will be presented and discussed.
References: [1] van Eijk C. W. E., Radiation Measurements 38 (2004) 337 [2] Yoshikawa A., Nikl M., Boulon G., Fukuda T., Opt. Mater. 30 (2007) 6 [3] Yoshikawa A., Chani V. I., MRS BULLETIN 34 (2009) 266
Synthesis and characterization of Ba2Cu1-xNixGe2O7, x =0, 0.1 single crystals grown by floating zone technique
Fittipaldi Rosalba1,2, Rocco Luisa1, Ciomaga Hatnean Monica3, Granata Veronica*1,2, Lees Martin3, Balakrishnan Geetha3, Vecchione Antonio1,2
1 Department of Physics, University of Salerno, Fisciano (Sa) (Italy) 2CNR-SPIN Salerno, Fisciano (Sa) (Italy) 3 Department of Physics, University of Warwick, Coventry, (United Kingdom) *email: [email protected]
In recent years, the understanding of the multiferroic properties, i.e. of the simultaneous presence of two or more coexisting ferroic orders, has been the topic of increasing interest. The attention to multiferroics has been mainly driven by the large magnetoelectric (ME) coupling shown by some distorted perovskites of transition metal (TM) oxides displaying both ferroelectric and magnetic properties. The study of the helimagnet Ba2CuGe2O7 is of great interest among the class of multiferroic compounds because it has been predicted that it could host a lattice of magnetic skyrmions. The study of all these complex phenomena requires the availability of good crystals. In this study high quality Ba2Cu1-xNixGe2O7 single crystals has been grown using the floating zone (FZ) technique, in different gas atmospheres and pressures. The excellent quality and perfect orientation of the crystals were confirmed by high resolution X-ray diffraction measurements. In Fig. 1 is shown the rocking curve of the (0 0 2) reflection proving the high crystallinity of the grown Ba2Cu1-xNixGe2O7 (x = 0) crystals. The crystals were also inspected by electron back scattered diffraction technique, these measurements allow to ascertain the absence of any misorientation on a microscopic scale supporting the results from X-ray measurements. XRD patterns and Rietveld refinement of crushed crystals showed diffraction peaks, all of which could be indexed to the Ba2Cu1-xNixGe2O7 phase, which means that crystals are pure. Compositional analysis has been carried out by WDS and they, also, put in evidence that the crystals don’t have spurious phases. The obtained crystals showed being suitable exploring the complex magnetoelectric phase diagram. Synthesis of large single crystals allows to investigate the fundamental physics of this material in order to identify the mechanisms responsible for its peculiar multiferroic properties.
Figure 1. Rocking curve of the (0 0 2) reflection acquired on Ba2Cu1-xNixGe2O7 (x = 0) single crystal
Crystallization of Al2O3-YAG-ZrO2 eutectic ceramic plates by the EFG technique
Laurent Carroz1, 2, Maya Cherif1, 3, Nicolas Barthaley2, José Peirrera2 and Thierry Duffar*3
1 SNECMA Villaroche, Rond-point René Ravaud, 77550 Réau, France 2 RSA, 380 Rue Rn 85 BP 16, 38560 Jarrie, France 3 SIMaP-EPM, UMR 5266 CNRS, 38402 Saint Martin d’Hères, France *email: [email protected]
The growth of eutectic oxides from the melt has been widely studied in the last decades. Indeed, due to their very specific 3D interconnected microstructure these materials offer exceptional mechanical properties at very high temperature [1]. Growth techniques (Bridgman, µ-pulling down, laser floating zone) and samples size obtained are still very varied according to laboratories, but currently, the Edge – defined Film – fed Growth (EFG) process was never mentioned to grow large crystals with adequate conditions for industrial production. Since the EFG technique allows growing shaped crystals directly from the melt, expensive and difficult post machining operations for these very hard materials can be avoided. Thus EFG process is an adequate growth technique for industrial crystal grower. In this context Al2O3-YAG-ZrO2 eutectic ceramic plates (cf. figure 1) were crystallized with the EFG process in Mo crucible and shaper, using an automated weight control system. Growth parameters had to be adjusted to maintain the shape while making sure to get a homogeneous 3D interconnected microstructure (cf. figure 1).
Figure 1. Al2O3-YAG-ZrO2 eutectic ceramic plates crystallized by the EFG technique and its interconnected microstructure as shown by SEM metallography.
References: [1] Y. Waku, Mechanical Properties and Thermal Stability of Oxide eutectic Composites at High Temperatures, Materials and Manufacturing Processes, 13 (1998), 6, 841-858.
New results in adsorption at semiconductor surfaces - consequences to growth and doping of semiconductor from the vapor
Stanisław Krukowski*1, Pawel Kempisty1, Pawel Strąk1, Maria Ptasinska2, Jacek Piechota2
11Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, Warsaw (Poland) 2Interdisciplinary Centre for Materials Modelling, Warsaw University, Pawińskiego 5a, Warsaw (Poland) *email: [email protected]
Results of ab initio simulations of adsorption of molecular and atomic species at semiconductor surfaces are discussed. A number of the growth species, including ammonia, hydrogen, silicon attachments to several semiconductor surfaces, such as GaN(0001), GaN(0001), AlN(0001) and SiC(0001) is discussed. A newly identified dependence of the adsorption energy on the charge transfer at the surface is identified and discussed. The DFT results necessary for the in-depth analysis of the processes are presented. It was proven that the adsorption energy, in addition to standard bonding term, is potentially supplemented by the electronic transfer contribution depending on the Fermi level. Thus the adsorption energy may vary by several electronvolts, depending on the Fermi level at the surface. It is shown that the predominant cases of the growth of semiconductor occurs in the condition when Fermi level is unpinned becoming free. Such surface state is may be analyzed using extended electron counting rule (EECR). In such condition the adsorption energy depends on the Fermi level position in the bulk, i.e. doping of the bulk semiconductor. The dependence of the adsorption energy on the Fermi level in the bulk provides basic explanation of the doping of semiconductors during growth. In addition, the atomic level mechanism of the transition of adsorption sites, incompatible to the crystal lattice, frequently obtained in ab intio simulations of the species at the semiconductor surfaces may be explained by electronic charge transfer. The results indicate that semiconductor crystal growth grow by the mechanism that is different from standard Burton, Carbera Frank (BCF) model.
Range of the temperature gradients and the growth rate values in the growth of CZT crystals from the melt
Repiso Eva1, Corrochano Álvaro1, Rubio Sandra1, Plaza Jose Luis1, Tsybrii Zinoviia2, Vuichyk Mykola2,Dieguez Ernesto*1
1Depart: Physics of Materials, Universidad Autónoma de Madrid (UAM), Madrid (Spain) 2Institute of Semiconductor Physics (ISP), Kiev, (Ukraine) *email: [email protected]
CdZnTe bulk crystals have been broadly employed in room temperature X-ray and gamma ray semiconductor detector applications due to their attractive physical-chemical material properties, in particular the high energy detection as an important parameter in medical imaging and homeland security applications. The presence of secondary phases, Te inclusions, dislocations, Cd vacancies, polycrystallinity, etc. are common facts that may cause the detector degradation, but that it can be reduced by adequate growth conditions. In fact, although it´s possible to build CdZnTe compact detectors for their use in the above mentioned applications, a tight control of a number of crystal growth parameters is needed to obtain high quality single crystal CdZnTe materials. The most often methods for growing large CZT crystals from the melt are Bridgman and Vertical Gradient Freeze techniques. Although they are both well-developed techniques, the lack of complete information about the growth parameters is a general fact in the publications on this field. For this reason, in this work we plan to validate the two most important growth parameters such as the growth rate (V) and the temperature gradients (G) in the solid (s) and in the liquid (l) in view of the heat balance equation in the solid liquid interface (SLI), taking into account known values for the thermal conductivities of the solid and the liquid (Ks, Kl). The range of the Gs and Gl versus V was examined by analyzing both experimental and simulated data obtained in the VGF technique. The Gs/V versus Gl/V representation gives a straight line where the slope is given by the ratio of the thermal conductivities Kl/Ks, being the range for an adequate V crystal growth value deduced from this figure. Moreover, the dependence of G in the solid and in the liquid on the V value shows that Gl has a negative dependence with V, while Gs linearly increases with the growth rate, giving the ratio of the Gs and Gl values the same as Kl/Ks when the growth rate is zero. Furthermore, the dependence of the product of thermal conductivities and the thermal gradient in the solid and in the liquid (KsGs, KlGl) on the growth rate shows that when V increases, Gl decreases and Gs increases to offset the product of LV. A complete view of the dependence of G on V using own and published experimental data, together with simulation results will be analyzed in this paper.
References:
[1]A. Natsume, N. Inoue, K. Tanahashi, A.Mori, Journal of Crystal Growth, 225 (2001) 221-224. [2] H. Bensalah, J.L. Plaza, J. Crocco, Q.Zheng, V. Carcelén, A. Bensouici, E. Diéguez, Applied Surface Science, 257 (2011) 4633-4636
Growth and Performance of Large ZnGeP2 Single Crystals
Chunhui Yang*, Zuotao Lei, Chongqiang Zhu, Liangcheng Song
Harbin Institute of Technology, No.92 West Da-Zhi Street Nan Gang District, Harbin (China) *email: [email protected]
Zinc germanium diphosohide (ZnGeP2) belongs to the chalcopyrite family with a direct band gap, and it has large nonlinear optical coefficient, a wide transparency range, sufficient birefringence and relatively high thermal conductivity[1]. All these physical properties make ZnGeP2 suitable for frequency conversion applications such as tunable mid and far-infrared optical parametric oscillator (OPO) laser systems. Firstly, ZnGeP2 polycrystalline ingots were synthesized by two-temperature method, and the maximum mass is about 500g for one run. The XRD and rocking curve suggest that they show chalcopyrite structure, high pure and good crystallinity. The ingots are suitable for growth as raw materials. Moreover, the study indicates that the more the charge amount, the higher the yield of product. Secondly, ZnGeP2 crystals were grown by Vertical Bridgman technique, and the largest size is about Φ50mm×140mm. The XRD and rocking curves suggest that they show good crystallinity and single phase, the XRF indicates that the as-grown ZnGeP2 is stoichiometric, and the absorption -1 coefficients of as-grown ZnGeP2 are 0.05-0.08cm at 2.05µm for o-light. However, the absorption -1 coefficients of annealed and irradiated ZnGeP2 reduce to 0.01-0.03cm at 2.05µm for o-light. The crystals are suitable for frequency conversion applications. Finally, the ZnGeP2 devices were tested for OPO. The ZnGeP2 crystals were cut to 6mm×6mm×(16-24)mm in sizes after thermal annealing. Both surfaces of the crystal were carefully polished and antireflection coated for pump, signal, and idler lights. The OPO output wavelengths were in the spectral range of 3-5 mm. The results suggest that the output power of 30W is obtained pumping at 2.09µm and the conversion efficiency is 56%[2]. Thus, ZnGeP2 is an excellent OPO material and is acceptable for the fabrication of the infrared nonlinear optical devices.
Figure 1. Typical ZnGeP2 devices with size of 6×6×(16-24)mm)
References: [1] Shay J L and Wernick J H, Pergamon Press, (1975) 1-244. [2] Zuotao Lei, Chongqiang Zhu, Chao Xu, Baoquan Yao, Chunhui Yang, Journal of Crystal Growth, 389(2014) 23-29.
Crystal growth, physical properties and applications of mixed and complex halides
Edith Bourret*, Zewu Yan, Eric Samulon, Tetiana Shalapska and Didier Perrodin
Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley CA (USA)
*email: [email protected]
The ability to make new materials is often key to major progress in fundamental physics and numerous applications. The field of scintillation is no exception. The pace of discovery of new scintillators has increased dramatically in the last few years after the discovery at the Lawrence Berkeley National Laboratory of efficient scintillation in new mixed and ternary halides [1-3]. Due to their property to emit light due to radiation interactions, these materials find uses in a variety of applications that such medical imaging, high energy physics experiments, mining and security. We will show that these materials are close to the fundamental limits in terms of luminosity, energy resolution, stopping power and response time. However they are often needed in the form of single crystals of large dimensions that is a challenge to achieve. We will present the current state of the growth of single crystals of mixed and complex halides. In particular we will discuss the issues stemming from raw materials purity, the hygroscopic nature of the compounds, the propensity to fracture during cooling and their phase diagrams. Mixed Ba halides are fully miscible and melt congruently. Figure 1 is an example showing a single crystal of BaBrCl, a mixed halide, with the melting/solidification behavior of that compound. Complex halides exhibit a variety of growth behavior. Results of engineering techniques aimed at improving the quality and performance of the single crystals will be discussed.
Figure 1. BaBrCl single crystal as grown (top) and under UV illumination (bottom) and the phase diagram of the solid solutions of BaBr2-BaCl2.
References: [1] ] E. D. Bourret-Courchesne, G. Bizarri, R. Borade, G. Gundiah, E.C. Samulon, Z. Yan, and S. E. Derenzo, Journal of Crystal Growth, 352 (2012) 78-83. [2] E. D. Bourret-Courchesne, G. Bizarri, S. M. Hanrahan, G. Gundiah, Z. Yan, and S. E. Derenzo, NIM A, 613 (01/21/2010) 95-97. [3] G. Bizarri, E. D. Bourret-Courchesne, Z. W. Yan, and S. E. Derenzo, IEEE Transactions on Nuclear Science, 58 (2011) 3403.
Modeling of dopant transport in gas and melt during silicon FZ crystal growth
Sabanskis Andrejs*1, Surovovs Kirils1, Virbulis Jānis1
1Faculty of Physics and Mathematics, University of Latvia, 8 Zellu str., LV-1002, Riga (Latvia) *email: [email protected]
The radial resistivity variation (RRV) is one of the most important quality criteria of a FZ grown single silicon crystal. The resistivity is controlled by adding dopants (impurities) to silicon, which are either incorporated in the feed rod or supplied though the atmosphere. The former case is considered in [1,2], while the latter, which is the most common nowadays, in [3]. However, a simplified concentration boundary condition is used in [3] at the free melt surface to model doping from the atmosphere, not considering dopant transport in gas. In the present work a 3D model for the calculation of dopant transport in gas in case of doping from the atmosphere is presented. For the calculation of the 2D shape of silicon phase boundaries and the 3D dopant transport in the melt the models described in [1] and [2] are used, respectively. Dopant transport in the gas and melt is coupled by the boundary conditions on the melting front and free melt surface. Results of numerical calculations are compared to the experimental RRV distribution [4]. An example of the created mesh on puller wall, poly- and monocrystal and two perpendicular planes in the gas is shown in Fig. 1 and the concentration field in the gas – in Fig. 2.
Figure 1. Fragment of 3D finite volume mesh.
Figure 2. Left: calculated concentration field (in logarithmic scale) in gas in vertical cross-sections. C = 1 at the inlet. Right: top view of the inductor and the definition of the cross-section planes.
References: [1] Ratnieks G., PhD thesis, University of Latvia (2007). [2] Lācis K., PhD thesis, University of Latvia (2010). [3] Larsen T. L., PhD thesis, Technical University of Denmark (2000). [4] Rost H.-J., Menzel R., Luedge A., Riemann H., Journal of Crystal Growth, 360 (2012) pp. 43–46.
Impact of growth rate fluctuations on the bulk quality of Czochralski silicon crystals
Gaspar Guilherme*1, Lanterne Adeline1, Jensen Øyvind2, Lehmann Toni3, Hagen Vegard4, Kildemo Morten4, Di Sabatino Marisa1, Arnberg Lars1, Øvrelid Eivind5
1NTNU, Department of Materials Science and Engineering, Alfred Getz vei 2B, Trondheim (Norway) 2IFE, Instituttveien 18, Kjeller (Norway) 3Fraunhofer THM, Am St.-Niclas-Schacht 13, Freiberg (Germany) 4NTNU, Department of Physics, Høgskoleringen 5, Trondheim (Norway) 5SINTEF Materials and Chemistry, Alfred Getz vei 2B, Trondheim (Norway) *email: [email protected]
During solar cell processing, striations tend to appear and variation of the electrical properties and consequently solar cell efficiency are observed [1]. The cause of the growth of striations has been associated to the melt-temperature fluctuations just below the solidification interface [2]. In the current work, striations formation in Czochralski-grown silicon was studied at different stages of the growth process with focus on the top of an industrial-scale ingot. Figure 1 shows the growth interface shape and crystallization instabilities found on a vertical cut on top of the ingot, as measured by Lateral Photovoltage Scanning (LPS) technique. A typical pull speed profile used during the growth of the block is also shown in the figure. Even though the pull speed of the crown has been set as a constant value, growth rate fluctuations are observed. The influence of the instability on the distribution of interstitial oxygen, defects, minority carrier lifetime and residual strain have been investigated. Variations of the ingot length and diameter have been monitored with 1 s time-resolution and the apparent crystal growth rate has been calculated. Afterwards, the growth rate distribution has been addressed to a 2D transient model of the Czochralski crystallization process (based on Sisim software) and fluctuations of the vacancy distribution have been determined and compared with the experimental results. Growth rate fluctuations have revealed a direct impact on interstitial oxygen, defects and residual strain distribution. As-grown lifetime has demonstrated to be mainly affected during large growth rate fluctuations.
Figure 1. LPS image of the ingot top investigated and corresponding input pull speed profile.
References: [1] Haunschild J., Reis I., Geilker J., Rein S., Physica Status Solidi, 5 (2011) 199-201. [2] Kanda T., Hourai M., Miki S., Shigematsu T., Tomokage H., Miyano T., Morita H., Shintani A., Journal of Crystal Growth, 166 (1996) 663-668.
Reduction of carbon contamination during the melting process of Czochralski silicon crystal growth
Xin Liu*, Bing Gao, Satoshi Nakano and Koichi Kakimoto
Research Institute for Applied Mechanics, Kyushu University,
6-1 Kasuga-Koen, Kasuga, Fukuoka (Japan) *email: [email protected]
Carbon (C) contamination in Czochralski (CZ) crystal growth of single crystalline silicon (Si) is detrimental for the minority carrier lifetime, which is one of the critical parameters of wafer for power device. Effective control of C concentration in the CZ-Si crystal is required for the production of high performance Si wafer. Contamination of C in Si crystal mainly originates from carbon monoxide (CO) generation on the graphite components. And, incorporation of C occurs prior to the growth stage. The reason is the CO generation starts from the preheating stage, and reaches the maximum in the melting stage of the CZ-Si crystal growth. To reduce the C contamination effectively, it is essential to control the C transport from its generation, incorporation and accumulation in the growth. For the reduction of CO generation, silicon carbide (SiC) coating could be applied to the gas guide above the melt surface. Enhancement of the argon (Ar) gas flow above the melt could reduce the incorporation rate of C. And, the accumulation time of C depends on the thermal history of the growth system. According to these principles, several strategies for reducing C contamination were investigated numerically in this work. Transient global simulations of heat and mass transport were conducted for melting process of CZ-Si crystal growth with different operating parameters. A virtual PID controller for the temperature was introduced to realize the power control of the heater. Besides the CO generation by the reaction between graphite and silicon monoxide (SiO), the reaction due to the contact between quartz crucible and graphite susceptor was also taken into account as another CO source. Accumulation of C in Si feedstock was predicted for the entire melting process, which consists of preheating, melting and stabilization stages. Effects of different strategies for C reduction were analyzed and compared. The SiC coating for the gas guide and the increase of Ar gas flow rate could suppress the C contamination significantly, as shown in Fig. 1. According to the accumulation of C, the final C content depends on the growth duration and contamination flux at the gas/melt interface.
(a) (b) Figure 1. Contamination of C in the melted Si. (a) Concentrations of C without coating (left) and with SiC coating (right); (b) Concentrations of C with Ar gas flow rate of 5 SLPM (left) and 10 SLPM (right).
N-type doping of bulk gallium nitride grown by hydride vapour phase epitaxy
Patrick Hofmann1*, Frank Habel2, Martin Krupinski1, Gunnar Leibiger2, Franziska Christine Beyer3, Stefan Eichler2, Thomas Mikolajick1,4
1NaMLab gGmbH, Nöthnitzer Straße 64, D-01187 Dresden, Germany 2Freiberger Compound Materials, Am-Junger-Löwe-Schacht 5, D-09599 Freiberg/Sa., Germany 3Institute of Experimental Physics, TU Bergakademie Freiberg, Leipziger Straße 23, D-09599 Freiberg/Sa., Germany 4TU Dresden, Institute for Semiconductors and Microsystems, D-01062 Dresden *email: [email protected]
Galliumnitride (GaN), as a representative of wide band gap semiconductors gathers attention because of its numerous applications in the high power device sector, as well as for optoelectronic applications [1]. The latter has a crucial necessity for doped material, since the pn-junction needs to be contacted in order to get light emitting or laser behaviour of the GaN material. The p-type doping is generally achieved by metalorganic chemical vapour deposition [2] during deposition of the device itself. Typically n-type GaN is used as base material for the deposition of the functional layers. Hydride vapour phase epitaxy (HVPE), as one of the industry relevant methods for growing bulk GaN, offers high crystal quality whilst keeping the unintentional doping level (UID) low [3]. It therefore qualifies for intentional doping experiments for providing n-type GaN wafers. Typically silicon (Si) [4,5] and germanium (Ge) [6] are used as n-type dopants for GaN. Both occupy the substitutional gallium (Ga) site in the GaN lattice [2]. Si doping leads to tensile stress generation in the GaN lattice, resulting in fracturing of the GaN crystals [7, 8]. This creates the need for special growth techniques before doping in order to avoid said fracturing [5]. It is reported, that Ge doping does not show this kind of behaviour [9], hence being the obvious alternative to Si doping. However, doping during bulk HVPE growth provides other challenges depending on the dopant source and growth parameters [10]. A detailed characterisation of the silicon doping using dicholorsilane has been carried out and the influences of the dopant incorporation on the bulk growth were investigated. The bulk GaN:Si crystals were investigated by confocal Raman- and catodoluminescence measurements to assess the strain situation of the samples. The crystal quality has been evaluated by X-ray rocking curve measurements. In dopant intake has been characterised by electrical and optical measurements and has been verified by mass spectroscopic methods. First results of the Ge doping during bulk HVPE growth will be discussed in comparison to the bulk Si doping of GaN.
References: [1] Ehrentraut, D. et al, Technology of Gallium Nitride Crystal Growth 1st ed. (Springer) chapter 1 (2010). [2] Morkoc, H. Handbook of Nitride Semiconductors and Devices 1st ed. (Wiley-VCH) (2008). [3] Ehrentraut, D. et al, Technology of Gallium Nitride Crystal Growth 1st ed. (Springer) chapter 9 (2010). [4] Richter E. et al. Phys. Stat. Sol. (a) 203 (2006) 1658–1662. [5] Richter E. et al. Electronic Materials 42 (2013) 820–825. [6] Oshima Y. et al. Journal of Crystal Growth 310 (2010) 3569–3573. [7] Brunner F. et al. J. Appl. Phys. 112 (2012) 033503–1–033503–5. [8] Romanov A. E. and Speck J S Appl. Phys. Lett. 83 (2003) 2569–2571. [9] Dadgar, A. et al. Applied Physics Express, 4 (2011) 011001-1–011001-3. [10] Yoon M. et al. Japanese Journal of Applied Physics, 44 (2005) 828–832.
Growth of 5 kg-level LBO for ultrashort and ultrahigh power laser
Zhanggui Hu*, Yinchao Yue, Ying Zhao, Heng Tu
Key Laboratory of Functional Crystals and Laser Technology of Chinese Academy of Sciences, Technical Institute of Physics and Chemistry, CAS, Beijing 100190, China
*Email: [email protected]
The growth of large size and high quality lithium triborate (LiB3O5, LBO) crystal is always the research hotspot in nonlinear optical crystal field because LBO crystal is widely used in solid-state laser technology. It is grown by the Top-Seeded Solution Growth method and Li2O-B2O3-MoO3 is currently considered as the most effective flux system. The LBO crystal grown in conventional methods weighs about 200g and the optical aperture is generally less than 10mm. With the development of high-energy, high-power laser technology, it is required that the LBO crystal has a higher quality and larger size. Our group made a breakthrough in large- size LBO crystal growth first in the world. The first, we designed a large flux crystal growth equipment to grow LBO crystals. The second, we adopted a new solute transport technique as well as a new flux system. The third, in order to process the large crystals we grew into larger diameter devices, we proposed a new method for the LBO crystal growth: near phase-matching angle direction growth. In 2007, we obtained 1 kg-scale LBO (1116.8g) crystal for the first time. In 2013, the largest LBO single crystal reported in the world with the size of 285×160×110 mm3 and the weight of 4798g was successfully grown in 180 days by us. In 2014, based on the the first 100×100×10 mm3 LBO device in the world we provided, a high power 32.0fs and 1.0 PW laser has been achieved through OPCPA, which represents the highest reported laser output in the world. In the meanwhile, we have achieved 510 W green laser using 15×5×100 mm3 LBO device, and may achieve KW power output soon. LBO device with the aperture of 150×150×10 mm3 has been fabricated for ongoing higher power laser experiment. Moreover, in the near future, LBO crystal with aperture larger than 250 mm will play an active role in the progress of large-aperture, high-energy, high-power laser techniques especially for OPCPA system, ICF, and fusion energy.
as grown LBO crystal: 240mm×160mm×110mm
POSTER
S04-P01 Bulk growth of optical quality inverted Solubility Li2SO4.H2O single crystals by the improved Sankaranarayanan -Ramasamy method
A. Silambarasan, P. Rajesh*, P. Ramasamy
Research Centre, Department of Physics, SSN College of Engineering, Kalavakkam-603110, Tamilnadu, India *email: [email protected], [email protected]
In the trend for the development of single crystals for second harmonic generation (SHG), Lithium Sulfate Monohydrate (LSMH) single crystal will undoubtedly attract more attention because of its good nonlinear optical coefficient and broad transparency range. The inverted solubility, pyroelectric behavior and higher density of LSMH makes difficult to grow as good quality bulk size single crystals. Also, the grown LSMH crystals have some defects and the transparency was poor due to spurious nucleation at the top region of the solution. In this work, significant modifications in the uniaxial solution-crystallization Sankaranarayanan - Ramasamy (SR) method was made in order to avoid such difficulties. Notably, bulk size LSMH single crystal was grown in short period with higher growth rate and excellent optical qualities than previous reports. The LSMH crystal grown by this method fulfilled all the requirements, such as a second harmonic response and splendid crystal characteristics including large crystal size with desired facets, higher laser damage stability, superior optical quality, wide transparency range, and controllable crystal thickness, which are in general extremely difficult to achieve simultaneously in single system. Therefore, the LSMH crystal could emerge as a potential candidate for applications in laser photonics and optoelectronic devices .
Figure .(a) Conventional grown LSMH (b) SR grown LSMH (c) SR grown LSMH with scale
S04-P04 TSFZ-growth, magnetism and ac conductivity of LiMn1-xFexPO4 single crystals
Christoph Neef*1, Hubert Wadepohl2, Hans-Peter Meyer3, Rüdiger Klingeler1
1Kirchhoff Institut für Physik, Universität Heidelberg, D-69120 Heidelberg (Germany) 2Anorganisch-Chemisches Institut, Universität Heidelberg, D-69120 Heidelberg (Germany) 3Institut für Geowissenschaften, Universität Heidelberg, D-69120 Heidelberg (Germany) *email: [email protected]
Olivine-structured materials LiMPO4 (M = Mn, Fe, Co, Ni) are one of the promising present and next generation cathode materials for lithium-ion batteries. In order to understand and to simulate the relevant processes associated with Li-(de)intercalation, information on the anisotropic Li- transport properties and on structural phase changes during intercalation is crucial. In addition to these partially application driven research demands, strong magneto-electric effects, magnetic frustration and unusual ferrotoroidal ordering phenomena raise more fundamental questions in this materials class as well. In the present work, mm-sized single-crystals of the series LiMn1-xFexPO4 (x=0, 0.3, 0.5, 1) were grown using the optical floating zone technique. Li2O volatilization during the melting procedure, which is typical for Li containing oxides, was strongly reduced by increasing the ambient pressure to 30 bar of purified Ar. The resulting samples are characterized by EDX and single crystal XRD showing a successful growth and the solid solution behavior between the end members LiMnPO4 and LiFePO4. SQUID magnetometry and thermal expansion studies at low temperatures imply antiferromagnetic order with the Neel temperature continuously shifting upon Fe doping from 33 K for LiMnPO4 to 50 K for LiFePO4. The composition dependent bulk conductivities of the series, which are of particular interest for application as battery material, are studied using ac impedance measurements. The ac conductivity strongly increases for Fe contents above x = 0.5 while it is low for the Mn rich compounds with x ≤ 0.3. Independent of the composition, there is an anisotropy in the ac conductivity between the crystallographic main axes amounting to about one order of magnitude, favoring the b-axis.
Figure 1. left: Oriented and cut crystal with compostion LiMn0.7Fe0.3PO4; right: Crystal structure according to single crystal XRD. PO4 tetrahedra in green, MO6 octahedra (M=Mn, Fe) in blue.
S04-P06 Czochralski growth of bulk Li2MoO4 crystals for the scintillating bolometers used in the rare events searches
Matias Velázquez*1, Pierre de Marcillac2, Andrea Giuliani2, Philippe Veber1, Dominique Denux1, Rodolphe Decourt1, Oudomsack Viraphong1
1CNRS, Université de Bordeaux, ICMCB, UPR 9048, 87 avenue du Dr. A. Schweitzer, 33608 Pessac cedex (France) 2Centre de Sciences Nucléaires et de Sciences de la Matière, CSNSM, UMR 8609, CNRS-Université d’Orsay, Bât. 108, 91405 Orsay Campus (France) *email: [email protected]
The search for the neutrino mass and the direct detection of the dark matter of our universe stand among the most exciting science drivers of today’s astroparticle physics. Crucial experiments in these domains require detecting extremely rare events, such as neutrinoless double beta decays (0-DBD) [1], or nuclear recoils induced by massive particles interacting weakly (WIMPS) with baryonic matter, considered as viable candidates to be the quantum components of the dark matter halo of our galaxy [2]. The DBD gives unique information about the neutrinos properties, their absolute mass scale, mass hierarchy and their nature. In addition, the direct detection of WIMPs would solve the recurring enigma on the very nature of dark matter, which is expected to constitute 26.8% of our universe’s content. Another rare event search with high discovery potential is the detection and spectroscopy of fast and extremely rare neutrons, which would help understanding the ultimate background of the dark matter direct detection underground sites. In all these cases, because of their high energy resolution and low energy threshold, heat-scintillation cryogenic bolometers (HSCBs) turn out to be very sensitive tools to carry out this exploratory research. HSCBs work at very low temperature (≤25 mK) and measure an energy release in a single crystal by means of both weak heat and light pulses resulting from the same nuclear event. HSCBs containing Mo as a constituent element have a tremendous potential in fundamental neutrino physics, especially if the detectors can be made with an extremely low content of radioactive impurities. Indeed, the isotope 100Mo, present at the 9.7% level in natural molybdenum, is an excellent candidate for a rare nuclear process known as 0-DBD. If observed, this decay would prove that neutrino is a Majorana particle, i.e. a fermion equal to its own anti-fermion or, in other words: a new type of matter. The implications of this fact would be long-reaching in fundamental physics, ranging from the understanding of the origin of the elementary particle masses to the explanation of the dominance of matter over anti-matter in the Universe. The core of HSCBs is made of radiopure bulk single crystals constituted as much as possible of nuclei that exhibit high capture cross sections of the relevant particles or that are themselves the source of the rare event to be detected. It just so happens that Li2MoO4 is a strategic crystal, because of the possibility to enrich it with 6Li, 7Li or 100Mo isotopes, the corollary absence of long-lived radioactive isotopes, its remarkable 232Th and 238U chains radiopurity, its sufficient light yield at low temperatures, its low and congruent melting point. In this talk, we will present our latest efforts to obtain bulk Li2MoO4 single crystals, of mass several hundred grams, by the seeded Czochralski method and discuss their growth conditions. Their characterization in terms of radiopurity levels (especially 40K), chemical purity and segregation, optical transmission, specific heat, differential scanning calorimetry and thermal expansion will also be reviewed.
References: [1] M. Tenconi et al., Physics Procedia, 61 (2015) 782-786. [2] G. Angloher et al., Physics of the Dark Universe, 3 (2014) 41-74.
S04-P07 Czochralski growth and physical properties characterizations of 6Li- and 10B- enriched crystals for heat-scintillation cryogenic bolometers used in the rare events searches
Matias Velázquez*1, Rekia Belhoucif1,2, Yannick Petit1, Olivier Plantevin3, Benoît Glorieux1, Oudomsack Viraphong1, Pierre de Marcillac3, Noël Coron4, Lidia Torres4, Philippe Veber1, Rodolphe Decourt1 1CNRS, Université de Bordeaux, ICMCB, UPR 9048, 87 avenue du Dr. A. Schweitzer, 33608 Pessac cedex (France) 2Faculté de Physique, Laboratoire d’Électronique Quantique, BP 32 El alia, 16111 Bab Ezzouar, Alger (Algeria) 3CSNSM, UMR 8609 CNRS-Université d’Orsay, Bât. 108, 91405 Orsay Campus (France) 4IAS, Bâts. 120-121, UMR 8617 Université Paris-Sud 11/CNRS, 91405 Orsay Campus (France) *email: [email protected]
Heat-scintillation cryogenic bolometers (HSCBs) are low threshold, high sensitivity, double readout detectors that measure simultaneously the heat and the light generated by a particle inside a crystal [1]. These detectors are being developed for dark matter direct detection [2], neutrinoless double beta decays, fast neutron spectroscopy, extremely long radioactive decays, among other rare events. A bolometer consists of a crystal absorber strongly coupled to a thermometer, both weakly coupled to a heat sink maintained at 10-30 mK. In this context, we are attempting to grow crystals with diameters of several centimeters and thicknesses several times the thermal neutron mean free path in 6Li-based crystals and the range of neutron capture induced particles in crystals made of 6Li or 10B, these mean free paths typically being 6 m for ’s and 34 m for tritiums in lithium borates. Since the 6Li and 10B isotopes, as well as several Gd isotopes, exhibit high neutron capture cross- -24 2 sections (10B-n4×6Li-n~6.10 cm @ 10 keV) [3], it soon turned out that crystals of the Li6Gd(BO3)3-type would constitute ideal candidates for both tailoring HSCBs with high light yields over a wide neutron energy range and adapting them to powerful light detectors working at low temperature and available from UV to X-ray spectral ranges. Moreover, in contrast with the 6LiF 6 10 bulk crystals that we had already obtained, Li6(Eu,Gd)( BO3)3 crystals are much less likely to exhibit thermoluminescence effects detrimental to HSCB applications [4]. In this poster presentation, we report on the crystal growth by combined Czochralski and Kyropoulos methods, 6 10 initiated on specifically oriented seeds, of centimeter-sized Li6Eu( BO3)3 and Li6(Eu,Gd)(BO3)3 single crystals with an heretofore unexplored concentration range for HSCBs operation. Their chemical purity, Gd depletion profiles and radiopurity levels are detailed. The most relevant physical properties, such as thermal conductivity, thermal expansion, mechanical hardness, polarized visible absorption and emission, specific heat combined with magnetic susceptibility and scintillation are discussed.
References: [1] H. Kraus et al., 2010, PoS(IDM2010) 109. [2] G. Angloher et al., Physics of the Dark Universe, 3 (2014) 41-74. [3] G. F. Knoll, In Radiation detection and measurement, 4th ed., J. Wiley & Sons (Ed.), 2010, chp. 14-15. [4] M. Martinez et al., J. Phys. : Conf. Ser., 2012, 375, 012025/1-4.
S04-P09 Influence of melt convection on the aggregation of inclusion in massive sapphire and garnet crystals for growing by HDC method
Nizhankovskyi S.V.*1, Tan’ko A.V. 1, Sidelnikova N.S. 1, Naydenov S.V. 1, Janovsky V.V. 1
1Institute for Single Crystals, State Scientific Institution “Institute for Single Crystals” of National Academy of Sciences of Ukraine, Lenin 60, Ave, 61001, Kharkiv, Ukraine *email: [email protected]
Sapphire and rare-earth garnet crystals possess a unique combination of physical and chemical properties; therefore they are widely used in optics, optoelectronics and laser technique. One of the main methods to obtain such crystals is a horizontal directed crystallization (HDC) method that allows growing crystals with different crystallographic orientation in the form of large size plates with a high homogeneity of the functional characteristics [1]. During massive crystals growing (plate thickness ≥ 30 mm) some "longitudinal" aggregation of inclusions (impurity phases, bubbles), distributed along the direction of crystal growth (Fig. 1 a), could appear. Such aggregation has a domelike shape with rounding to the lateral sides of the crystal, which allows us to suggest that defects appear at some specific convection conditions in the melt (Fig. 1 b) [2]. With numerical simulation we analyzed convection in sapphire (Al2O3) and garnet (YAG) melt and the thickness of the diffusion layer in the vicinity of the crystallization front as a function of melt overheat, geometrical parameters of the melt zone (height h and length L) and the crystallization front shape. It was established that the longitudinal aggregation generation is caused essentially by a diffusion layer local thickening in the contact region of two flows (thermocapillary and buoyancy-driven flow) (Fig. 1c). Convective flows capture bubbles and impurities and transfer them to this contact region, where they are accumulated and defect aggregation is formed. It is shown that choice of optimal temperature growth conditions and geometrical parameters of the melt zone allows to grow massive (up to h > 50 mm) sapphire and garnet crystals by HDC method without defect aggregation [3].
Figure 1. Longitudinal (a) and cross (b) section of sapphire crystal containing inclusions; the two- vortex motion of melts and diffusion layer in the vicinity of the crystallization front (c)
References: [1] S.V. Nizhankovskii, N.S. Sidel`nikova, V.V. Baranov, Physics of the Solid State, V.57, (2015), pp. 781-786. [2] Dan’ko A., Nizhankovskiy S. V., Puzikov V. M., Crystallography Reports, V.53 (2008), pp. 1272–1275. [3] Nizhankovskyi S., Tan’ko A., Sidelnikova N., Adonkin G. Cryst. Res. Technol. 50, No. 3, 223-229 (2015).
S04-P10 Range of the temperature gradients and the growth rate values in the growth of CZT crystals from the melt
Repiso Eva1, Corrochano Álvaro1, Rubio Sandra1, Plaza Jose Luis1, Tsybrii Zinoviia2, Vuichyk Mykola2,Dieguez Ernesto*1
1Depart: Physics of Materials, Universidad Autónoma de Madrid (UAM), Madrid (Spain) 2Institute of Semiconductor Physics (ISP), Kiev, (Ukraine) *email: [email protected]
CdZnTe bulk crystals have been broadly employed in room temperature X-ray and gamma ray semiconductor detector applications due to their attractive physical-chemical material properties, in particular the high energy detection as an important parameter in medical imaging and homeland security applications. The presence of secondary phases, Te inclusions, dislocations, Cd vacancies, polycrystallinity, etc. are common facts that may cause the detector degradation, but that it can be reduced by adequate growth conditions. In fact, although it´s possible to build CdZnTe compact detectors for their use in the above mentioned applications, a tight control of a number of crystal growth parameters is needed to obtain high quality single crystal CdZnTe materials. The most often methods for growing large CZT crystals from the melt are Bridgman and Vertical Gradient Freeze techniques. Although they are both well-developed techniques, the lack of complete information about the growth parameters is a general fact in the publications on this field. For this reason, in this work we plan to validate the two most important growth parameters such as the growth rate (V) and the temperature gradients (G) in the solid (s) and in the liquid (l) in view of the heat balance equation in the solid liquid interface (SLI), taking into account known values for the thermal conductivities of the solid and the liquid (Ks, Kl). The range of the Gs and Gl versus V was examined by analyzing both experimental and simulated data obtained in the VGF technique. The Gs/V versus Gl/V representation gives a straight line where the slope is given by the ratio of the thermal conductivities Kl/Ks, being the range for an adequate V crystal growth value deduced from this figure. Moreover, the dependence of G in the solid and in the liquid on the V value shows that Gl has a negative dependence with V, while Gs linearly increases with the growth rate, giving the ratio of the Gs and Gl values the same as Kl/Ks when the growth rate is zero. Furthermore, the dependence of the product of thermal conductivities and the thermal gradient in the solid and in the liquid (KsGs, KlGl) on the growth rate shows that when V increases, Gl decreases and Gs increases to offset the product of LV. A complete view of the dependence of G on V using own and published experimental data, together with simulation results will be analyzed in this paper.
References:
[1]A. Natsume, N. Inoue, K. Tanahashi, A.Mori, Journal of Crystal Growth, 225 (2001) 221-224. [2] H. Bensalah, J.L. Plaza, J. Crocco, Q.Zheng, V. Carcelén, A. Bensouici, E. Diéguez, Applied Surface Science, 257 (2011) 4633-4636
S04-P11 Growth and Laser performance of a new IR NLO crystal BaGa4Se7
Yao Jiyong*1, Yang Feng1, Wu Yicheng1; Xu Zuyan1
1 Technical Institute of Physics and Chemistry, CAS, , Beijing (China) *email: [email protected]
BaGa4Se7 is a new IR NLO crystal recently discovered by us. It possesses a number of advantages including large NLO coefficients（d11=24pm/V), high transparency in the wide range of 1-14 µm, high laser damage threshold, and large birefringence. High quality Φ30mm×70mm crystals have been obtained. Preliminary optical parametric experiments have achieved high efficiency and high peak power “3-11µm” laser output, and optical rectification has also realized narrow band 2Thz output. These results indicate BaGa4Se7 is a very promising new IR NLO crystal.
Figure 1. Φ30mm×70mm BaGa4Se7 crystal Figure 2. The tuning performance in 3–5μm
THz Signal in Frequency Domain 90.0p
f=1.936THz
60.0p
30.0p Amplitude (A.U.)
0.0 0.51.01.52.02.5 Frequency (THz)
Figure 3. The tuning performance in 6.4–11μm Figure 4. Narrow band Thz output
S04-P12 Growth from the melt, structure and properties of the crystals of (ZrO2)1-x(Sc2O3)x solid solutions
Borik Mikhail1, Bredikhin Sergey2, Kulebyakin Alexey*1, Kuritsyna Irina2, Lomonova Elena1, Milovich Filipp3, Myzina Valentina1, Osiko Vyacheslav1, Panov Vitaliy1, Seryakov Sergey3, Tabachkova Nataliya3
1A.M. Prokhorov General Physics Institute RAS, Vavilov Str., 38, 119991, Moscow (Russia) 2Institute of Solid State Physics RAS, Institutskaya str., 2, 142432, Chernogolovka (Russia) 3National University of Science and Technology «MISIS», Leninsky pr., 4, 119049, Moscow (Russia) *email: [email protected]
Single crystals of (ZrO2)1-x(Sc2O3)x solid solutions were grown using directional melt crystallization in a water-cooled copper crucible diameter of 130 mm. Crystal growth was carried out on the "Kristall-407" (frequency - 5.28 MHz, the maximum output power of 60 kW). The weight of the material that was loaded into the cold container was approximately 6 kg. Directional melt crystallization was conducted by moving the crucible with the melt relative to the inductor at a rate of 10 mm/h. Were grown crystals of (ZrO2)1-x(Sc2O3)x solid solutions with x = 0.035, 0.06, 0.09, 0.11. The crystals have a columnar shape; typical crystal size is 20-30 mm - length and 10-15 mm - cross section. For crystals containing 3.5 and 6 mol% Sc2O3 is characterized by the presence of cracks in the crystal after the growth. Analysis of the scandium oxide distribution on the length of the crystal showed that the composition of all the samples is homogeneous and Sc2O3 concentration practically corresponds to its content in the starting material. All the studied samples show a low tendency to decrease of the concentration of Sc2O3 along the crystal, which indicates that the effective distribution coefficient Sc2O3 slightly greater than 1. Phase composition and structure of the crystals studied by x-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). It is found that the crystals have a different phase composition depending on the concentration of scandium oxide. The samples containing 3.5 mol% Sc2O3 is characterized by the presence of the monoclinic and tetragonal phases. The samples with 6 mol% scandium oxide have a tetragonal structure. In the crystals with 9 mol% Sc2O3 concentration presented tetragonal phase with a mixture of rhombohedral phase. The specimens containing 11 mol% Sc2O3 consist only of rhombohedral phase. The identity of the phase composition of crystals during their studies by the above methods indicates the absence of phase transitions in these crystals induced by mechanical stress. It is important to note that all samples are not detected the presence of the cubic phase. For all investigated crystals is characterized by twinned structures of different types and sizes depending on the composition. Physico-chemical properties of the crystals, such as density, microhardness and crack resistance were measured. It is shown that the crystals have a high hardness, but low crack resistance. The data on the measurement of the temperature dependence of the electrical conductivity of crystals containing 6 and 9 mol% Sc2O3 are presented. As a result of our preliminary experiments we were obtained large, homogeneous, optically transparent single crystals in the system ZrO2-Sc2O3-Y2O3. At the present time we study properties of the crystals. The work was supported by research grant № 14-29-04081 of the Russian foundation for basic research (RFBR) ofi-m.
S04-P13 Bulk crystals of L-Histidinium dihydrogen phosphate orthophosphoric acid grown by Sankaranarayanan - Ramasamy method
Reena Ittyachan a , A.Arunkumar b
a Department of Physics, Sacred Heart College, Chalakudy, Kerala- 680307, India b SSN Research Center, SSN college of Engineering, Kalavakkam- 603 110, India
Transparent L-Histidinium dihydrogen phosphate orthophosphoric acid (LHDP) crystal of length 80 mm long and 20 mm diameter has been grown from aqueous solution along c-axis using Sankaranarayanan - Ramasamy method. The unit cell parameters were confirmed by single crystal X-ray diffraction analysis and it belongs to orthorhombic system. The crystalline perfection of grown crystals was analyzed by High-resolution X-ray diffraction. The UV-vis-NIR spectrum showed that the grown crystal is transparent in the entire visible region. . The lower optical cut-off wavelength for this crystal was observed at 240 nm. Fluorescence studies were carried out in range of 200 – 700 nm. Thermogravimetric and differential thermal analysis was carried out to determine the thermal property of the grown crystal. The mechanical property of the grown crystal was studied by Vickers Microhardness measurement. The third order nonlinear refractive index (n2), nonlinear absorption coefficient (β) and susceptibility (χ(3)) were calculated by Z-scan studies using Nd: YAG laser as a source. It is found that the AAP molecule is a potential candidate for optical limiting applications. The laser damage threshold was measured using Q-switched Nd: YAG laser (1064 nm).
Photograph of SR grown ammonium acid phthalate single crystal.
S04-P15 Control of sapphire crystal morphology grown in a Kyropoulos furnace
Gourav Sen*1, Guillaume Alombert-Goget2, Cyril Pezzani3,Nicolas Barthalay3, Thierry Duffar1, Kheirreddine Lebbou2, Bruno Delagenière4
1SIMAP-EPM, UMR 5266 CNRS, 38402 Saint Martin d’Hères (France) 2Institut Lumière Matière, Université Lyon 1-UMR 5306 CNRS, 6922 Villeurbanne (France) 3RSA le rubis SA, BP 16, 38560 Jarrie/Grenoble (France) 4Cyberstar, Parc Sud Galaxie - 1, rue des Tropiques - 38130 ECHIROLLES (France) *[email protected]
The Kyropoulos method is used to grow large sized titanium-doped sapphire single crystals for power laser applications. However these crystals possess some huge macroscopic defects like bubbles and haze which render a large bulk of the crystal unworthy for use. The crystal shape evolution during the growth process influences the presence of these defects and hence an effort was made to study the crystal shapes as an effect of varying growth parameters. A comparison was made on various grown crystals to establish the relationship between the morphological defects and the growth parameters. An ideal growth process has been defined with the growth parameters for different stages of evolution of the crystal. An automated method of growth process control was developed to maintain those parameters and thus obtain crystals of a superior quality.
A) B)
Figure 1.Titanium doped Sapphire ingots obtained by Kyropoulos method; A) Ingot obtained by manual control of growth parameters, B) Ingot obtained by automatic control
S04-P16 Influence of Growth Conditions in Interface shape and Stability in Antimony doped Germanium Single Crystals using VB, AHP, and AVC Techniques
Sheikhi Aidin*1, Yousefi. L Pouya1, Balikci Ercan1
1Bogazici University,Department of Mechanical Engineering 34340 Bebek, Istanbul (Turkey) *email: [email protected]
Single crystal growth of antimony doped germanium is investigated by Vertical Bridgman (VB) [1], Axial Heat Processing (AHP) [2], and Axial Vibrational Control (AVC) [3] techniques. In order to achieve homogeneous crystals, stability of a planar interface should be maintained during the growth. To this end, effective parameters on morphological stability such as melt height, temperature gradient, and growth rate should be studied carefully. AHP method provides accurate data for such investigation. This method is similar to VB method. The crystallization takes place in a vertical cylindrical crucible which is surrounded by 4-zone furnace that establishes axial temperature gradient along the crucible. In order to reduce the melt height and effects of natural convection, a submerged baffle is used inside the crucible. Additionally, in the AVC method, the axially vibrating submerged baffle can modify the heat and mass transfer ahead of the growth interface in a desired way by optimizing the amplitude and frequency of the vibration and distance of the baffle from the interface. Hence, the vibrating baffle mixes the melt region under the baffle that can promote a planar interface, reduce radial temperature gradient, and homogenize radial solute distribution. In order to investigate the interface shape and solute segregation, the grown crystals are axially cut into two halves. Then, the surface of one half is ground, polished, and electro-etched to visualize striation lines which show position and shape of the interface during the growth. Also, radial and axial solute concentration in each crystal is measured by the four-point probe technique on the polished surface. Moreover, morphological stability of the grown crystals in different techniques is compared to each other. Results show that the stability is enhanced for the crystal grown with the AVC technique by applying 2 mm amplitude and 0.25 hertz frequency to the vibrating baffle. It has been observed that solute segregation is reduced, interface shape becomes more planar, and the single crystal length is increased up to 180 percent in comparison to the crystal grown with the VB method.
References: [1] P. W. Bridgman, “Various Physical Properties of Rubidium and Cesium and the Resistance of Potassium Under Pressure”, Proceedings of the American Academy of Arts and Sciences, 60 (1925) 385. [2] E. Balikci, A. Deal, R. Abbaschian, et al, Crystal Growth & Design, vol. 4, No 2, (2004), pp. 377-381. [3] I. K. Avetisov, A. Y. Melkov, A.Y. Zinovev, E. Zharikov, “Growth of nonstoichiometric pbte crystals by the vertical Bridgman method using the axial-vibration control technique”, Crystallography Reports, 50 (1) (2005) S124-S129.
The study is supported by TÜBİTAK, TURKEY, grant no 212M030.
S04-P19 VGF growth of GaAs doped with 12C, 16O and 18O for the study of mid- infrared vibrational modes
Christiane Frank-Rotsch1, Alexander Glacki2, Hans Christian Alt3, Hans-Edwin E. Wagner3
1 Leibniz Institute for Crystal Growth, Max-Born-Str. 2, 12489 Berlin (Germany) 2present address: Schott AG, Hattenbergstr.10, 55122 Mainz (Germany) 3University of Applied Sciences, Lothstr. 34, 80335 Munich (Germany) *email: [email protected]
Various growth experiments were conducted for an aimed doping of bulk GaAs with carbon 12C, and oxygen isotopes 16O and 18O. Aim was to identify the origin of the sharp absorption band at 2060 cm-1 in annealed GaAs crystals, which was hitherto attributed to the local vibrational mode of a complex containing both C and O [1]. 4’’-GaAs crystals with weight of about 1 kg were grown by the Vertical Gradient Freeze technique under the influence of traveling magnetic fields [2] for the improvement of melt stirring, stabilization of the growth process, and the enhancement of the dopant incorporation [3]. High carbon concentrations were achieved by adding roughened graphite plates to the melt. Oxygen was introduced either by adding various quantities of boron oxide or/and GaOOH to the crucible (see 16 18 Fig. 1). The GaOOH was synthesized using either conventional H2 O or H2 O and Ga. The B2O3 16 18 was either dry with 200 ppm water content or wetted by H2 O and H2 O in different volume ratios. Low-temperature Fourier transform infrared absorption measurements of a GaAs sample with a total oxygen concentration of 3.4x1015 cm-3 and an enrichment of the 18O isotope (16O:18O~30:1) revealed that the satellite band of 2060 cm-1 at 2050 cm-1, which was previously attributed to the 18O isotope, was not enhanced in comparison with spectra containing the natural oxygen isotope ratio (500:1) [4]. This ruled out any defect model involving oxygen atoms. The origin of the 2060 -1 cm mode was subsequently identified as a complex of the composition CN2 by implantation of the isotopes 14N and 15N into standard semi insulating GaAs wafers.
Figure 1: Crucible equipment for growth experiments for an aimed doping with 12C, 16O and 18O: a) 18O 18 18 was introduced by adding GaOOH b) O was introduced by wetting the B2O3 with H2 O before growth
References: [1] W. Ulrici and M. Jurisch, Phys. Status Solidi B 242, 2433 (2005) [2] Frank-Rotsch et al., J. Crystal Growth 401, 702-707 (2014) [3] Glacki et al., J. Crystal Growth 397, 6-12 (2014) [4] H. Ch. Alt et al., submitted to Phys. Status Solidi B (2015)
S04-P20 The search for novel solvents for the single crystal growth of germanate phases by the flux method
Ivanov Vladimir *1, Marychev Mikhail 1, Andreev Pavel 1, Koseva Iovka 2, Tzvetkov Peter 2, Nikolov Velin 2
1 N.I. Lobachevsky State University of Nizhni Novgorod, Nizhni Novgorod (Russia) 2 Bulgarian Academy of Science, Institute of General and Inorganic Chemistry, Sofia (Bulgaria) *email: [email protected]
A series of alkali-borate (Na2O·B2O3, Na2O·1.5B2O3, Na2O·2B2O3 and Li2O·B2O3), and a series of alkali-molybdate (Na2O·1.5MoO3, Na2O·2MoO3 and Li2O·MoO3) solvents were studied with a view to find out the suitable conditions for growing single crystals from germanate phases by the flux method. The ternary systems solvent-CaO-GeO2 were investigated and crystallization temperature and crystalized phase were determined. As a main result the concentration and temperature regions of crystallization of calcium germanates (Ca5Ge3O11, CaGeO3) and of some alkali germanates (Li2GeO3, Li2CaGeO4, Na2CaGe6O14) were experimentally determined for a first time. The conditions found for Ca2GeO4 growth are significantly more favorable than those known so far. The results of the performed study give a basis for producing single crystals by the flux method from a series of germanate compounds with various application areas. Cr4+-doped single crystals of Ca2GeO4, which are among the best prospective materials for solid state lasers emitting in the 1.1- 1.6 μm range, can be successfully grown from a Na2O·B2O3 solvent, as well as from a Li2O·B2O3 solvent [1]. Although the solutions contain high amounts of CaO and GeO2, there is no noticeable evaporation and the viscosity is of the order of 60 cP. The initial crystallization temperature that o could be used is about 1150 C which is considerably lower than that with the solvent CaF2 used so o far (above 1350 C) [2]. The problems encountered upon using CaCl2 as a solvent are also eliminated (evaporation, hygroscopicity) [2, 3]. The same solvents can be used for growing single crystals of Ca5Ge3O11 (another potential laser o o matrix) and single crystals of CaGeO3 with crystallization temperatures of about 1050 C - 1100 C [1]. The recommended conditions for growing lithium germanates (Li2GeO3 and Li2CaGeO4) from a Li2O·MoO3 solvent are also given. The crystallization regions of the two phases are rather broad and the crystallization temperatures are in the range of 950-1050oC. Special attention was paid to the possibility of growing single crystals from (CaLi)2GeO4 solid solutions from the system Li2O·MoO3 – CaO – GeO2. The preserved olivine structure of Ca2GeO4 with partial substitution of Ca for Li is a potentiality for alteration of the optical properties of Ca2GeO4. The research is supported by a grant (agreement of August 27, 2013 № 02.В.49.21.0003 between the Ministry of Education and Science of the Russian Federation and N.I. Lobachevsky State University of Nizhni Novgorod).
References: [1] Ivanov V.A., Marychev M.O., Andreev P.V., Koseva I., Tzvetkov P., Nikolov V., J Cryst. Growth. Available online 9 May 2015. DOI: 10.1016/j.jcrysgro.2015.04.042 [2] Bykov A.B, Petricevic V., Steiner J., Yao Di, Isaacs L.L., Kokta M.R., Alfano R.R., J Cryst. Growth V. 211 Issues 1–4 (2000) 295-301. DOI: 10.1016/S0022-0248(99)00770-8 [3] Nishi F., Takéuchi Y., Acta Crystallogr. C V. 40 Part 5 (1984) 730-733. DOI: 10.1107/S0108270184005515
S04-P21 The reduction of basal plane dislocations by modifying thermal conductivity of the crucible during PVT growth of 4H-SiC single crystals
Kazuma Miyazaki*1, Bing Gao2, Satoshi Nakano2, Koichi Kakimoto1, 2
1Dept. Aeronautics and Astronautics, 744, Motooka, Nishi-ku, Fukuoka 819-0395 (Japan) 2RIAM, Kyushu University, 6-1, Kasuga-koen, Kasuga, Fukuoka 816-8580 (Japan) *email: [email protected]
SiC is expected as the power device material which replaces Si and makes energy saving achieved. The physical vapor transport (PVT) method is the most practical and commonly used method to grow bulk SiC crystals. However, reduction of dislocation density by the PVT growth is more difficult than other growth methods of the SiC single crystals. In this study, we performed a numerical analysis of the reduction of basal plane dislocation (BPD) density in SiC single crystals. In this analysis, we modified thermal conductivity of a part of the graphite crucible constituting a crystal growth furnace and examined variation of the BPD density.In our numerical analysis, we substitute the resolved shear stress into the Alexander-Haasen model proposed by Gao et al. to obtain the BPDs [1]. 4H-SiC crystals have three primary slip directions in the (0001) basal plane, and the rate of the mobile dislocation density in slip direction is given by
(1) where the subscript m denotes the mobile dislocation, is the stress exponential factor, N is the dislocation density, K is the multiplication constant, is the effective stress for dislocation multiplication, and is the slip velocity of dislocation. In additin to this equation, fluctuates by , and is decided by the resolved shear stress in primary slip direction [2]. Thus, the BPD density depends on , and it finally greatly depends on the stress [3]. Thermal conductivity of the graphite crucible that we set is as follows (where is the temperature):
(2)
Figures 1 and 2 show distributions of BPD and temperature with the two different thermal conductivities at the time of the growth end. We set the heater power and pressure in a furnace kept constant as 18kW and 1 Torr, respectively. Figure 1 shows that lower BPD could be resulted in the lower thermal conductivity of the material. This is due to the result of lower radial heat flux ( ) and the gradient of the flux ( ) shown in Fig. 2 [2].
Figure 1. Comparison of the BPD density Figure 2. Comparison of the temperature (left half: , right half: ) distribution (left half: , right half: )
References: [1] B. Gao, K. Kakimoto, J. Cryst. Growth, 386 (2014) 215 [2] B. Gao, K. Kakimoto, Cryst. Growth Des. , 14 (2014) 1272 [3] K. Bottcher, K. Andrew Cliffe, J. Cryst. Growth, 303 (2007) 310
S04-P22 Dosimetric properties of luminescence crystals grown by Micro-Pulling Down Method
B. Marczewska, P. Bilski, W. Gieszczyk, M. Kłosowski, A. Twardak, D. Wróbel
Institute of Nuclear Physics PAN, ul. Radzikowskiego 152, 31-342 Kraków, Poland e-mail:[email protected]
Ionizing radiation is more and more widely used in many areas of life such as medicine, industry and science. Individual radiation protection of workers as well as environmental monitoring are most often conducted by passive detectors based on luminescence materials. Besides LiF which is commonly applied in thermoluminescence (TL) method of dose measurement and Al2O3 used in optically stimulated luminescence (OSL), there is still a need for seeking the new luminophors. The most promising new materials appear to be lithium aluminate (LiAlO2) and lithium magnesium phosphate doped with terbium and boron (LiMgPO4:Tb,B). Both of them are especially interesting due to the presence of Li-6, which gives them the potential ability to be applied as dosimeters in neutron fields. The aim of the work is to investigate the dosimetric properties of LiAlO2 and LiMgPO4 crystals as OSL dosimeters in regard to their sensitivity to the radiation, repeatability of the OSL signal and dose response. Crystals were grown by Micro-Pulling Down method at IFJ PAN in Kraków. Crystals were pulled down from iridium crucibles in the argon atmosphere with different growth rates from 0.1 to 20 mm/min. The crystals in the form of rods with the diameter of about 2 mm and the length of 10 cm were cut to smaller slices. The luminescence of the samples was investigated with OSL method in an automated TL/OSL reader (model DA-20) produced by Risoe National Laboratory, Denmark. OSL measurements were done using blue diodes (470 nm ± 30 nm) for stimulation. The readouts were performed using an U340 optical filter transmitting 250-400 nm light wavelength. The samples were irradiated with beta rays from 90Sr/90Y and alpha particles from 241Am sources built-in TL/OSL reader. The sensitivity of the LiAlO2 and LiMgPO4 crystals to the ionizing radiation is very high and can even exceed the sensitivity of commercially available Al2O3:C detectors. The crystals show good dose response which is linear in the dose range from 0.01 mGy to 1 kGy for irradiation with beta rays. The dependence of dosimetric properties of LiAlO2 and LiMgPO4 crystals on growth conditions, feed material composition and dopants will be discussed.
Acknowledgments: This work was supported by the National Science Centre (Contract No. DEC-2012/05/B/ST5/00720) and party by the Polish Ministry of Science and Higher Education within Iuventus PLUS IV program (2015 - 2017), project no. IP2014 011973.
S04-P23 Optical, Structural and Microhardness Properties of KDP Crystals Grown from L-arginine Doped Solutions
Igor Pritula*1, Olga Bezkrovnaya1, Elena Kostenyukova1, Dmitriy Sofronov1, Elena Dolzhenkova1
1 Institute for Single Crystals SSI “Institute for Single Crystals” NAS of Ukraine, 60, Lenin Avenue, 61001, Kharkiv (Ukraine) *email: [email protected]
The hydrogen bonds present in KDP group crystals essentially contribute to nonlinear optical phenomena such as quadratic electrooptical effect and generation of higher harmonics. To raise the quadratic susceptibility and, consequently, the efficiency of the three-wave processes in these crystals, in a number of investigations, for instance [1, 2], there were made attempts to incorporate organic molecules, in particular, low-dimensional molecules of amino acids, into KDP group crystals. Such molecules possess high polarizability due to the processes of internal charge transfer - + between the donor (COO ) and the acceptor (NH2 ) amino acid groups. In the present work we studied peculiarities of the incorporation of L-arginine (L-Arg) into KDP crystal grown by the method of temperature reduction onto a point seed. The influence of the low-dimensional organic additive on the optical properties, structure perfection, mechanical and laser damage threshold of KDP crystal was investigated, too. KDP single crystals were grown from aqueous solutions onto a point seed using the temperature reduction method by doping with different (from 0.3 to 1.4 wt.%) concentrations of L-Arg. The polydentate characters make L-Arg more advantageous for long-range hydrogen bonding interactions, or electrostatic interactions with positively charged groups. The optical transmission spectrum of KDP:L-arg showed very low absorption in the entire visible region. We have observed in the spectral changes the interaction between host material (KDP) and the guest amino acid additive (L-Arg). The presence of the functional groups belonging to L-Arg molecule was confirmed by FTIR-spectroscopy. The performed Raman spectroscopic studies showed that the 3− band of the normal modes of the tetrahedral PO4 ions were affected when the additives were used. L-Arg molecules were found to enter in the growth sectors {100} and {101} of KDP crystal, either due to the fact that the carboxyl and amino groups formed hydrogen bonds with the face (100) in the former case, or, in the latter case, owing to the electrostatic interaction of the negatively charged carboxyl groups with the positively charged (101) face. By means of the Bond method using a multipurpose three-crystal X-ray diffractometer it was shown that the presence of L-Arg additive increased the crystal lattice parameter a of the grown crystals, and diminished the crystal lattice parameter c. For the first time, there was analyzed the influence of L-arg molecules on the value of laser damage threshold for different growth sectors of KDP. The laser damage threshold was found to rise for the growth sector {101}, and to decrease for the growth sector {100} of KDP:L-Arg with respect to the corresponding values for the pure crystal. The Vicker`s hardness studies performed at room temperature on the (100) and (001) crystallographic planes showed that the doping with amino acid resulted in the decrease of the crystal’s microhardness by 5-9% and 14-18% for the pyramidal and prismatic growth sectors, respectively.
References: [1] Govani J., Durrer W., Manciu M., Botez C., Manciu F., J. Mater. Res., 24 (2009) 2316. [2] Mena M., Mahadevan C., Cryst. Res. Technol., 43 (2008) 166.
S04-P24 Growth and point defect characterization of bulk AlN crystals Carsten Hartmann, Andrea Dittmar*, Jürgen Wollweber, Sandro Kollowa, Klaus Irmscher, Frank Langhans, Albert Kwasniewski, Matthias Bickermann
Leibniz Institute for Crystal Growth (IKZ), Max-Born-Str. 2, 12489 Berlin (Germany)
A Bulk AlN crystals with high structural perfection are a highly promising substrate material for opto-electronic deep UV AlGaN devices with emission wavelengths λ < 300 nm where dislocation densities DD < 106 cm-2 are required in the active layers to achieve acceptable quantum efficiencies. From our present point of view, the homoepitaxial bulk growth by Physical Vapour Transport (PVT) is the commonly accepted method for growing crystals of sufficient size and crystalline quality (DD < 105 cm-2, no small-angle grain boundaries). In this work, we report on the PVT growth of high quality single crystalline AlN based on the comparatively small size of spontaneously nucleated AlN crystals. Therefore, a continuous crystal enlargement is mandatory which can be realized during homoepitaxial growth over several growth generations. Parallel to that, incorporation of impurities like O, C, and Si during growth has to be considered, as they influence the crystal’s optical and electrical properties. Ways to control the incorporation of these impurities during the PVT growth are pointed out. Single AlN crystals grown by PVT were structurally characterised by rocking curves, X-ray Lang topography, and defect-selective wet chemical etching. The crystalline perfection of the initial seed wafers (rocking curve FWHM 11-20 arcsec) can be preserved during smooth crystal enlargement over several crystal generations. Currently, crystals of up to 15 mm diameter with rocking curve FWHM values between 13 and 21 arcsec across the whole surface area are obtained (DD < 104 cm-2)[1]. O, C, and Si impurity concentrations derived from crucible as well as AlN source material are determined by secondary ion mass spectrometry (SIMS). It is demonstrated that the impurity incorporation can be influenced by the growth temperature, by face specific growth, and by adding impurities into the source material. UV measurements have proven that the broad absorption band centered at about 265 nm impairing deep-UV applications can be quenched when O or/and Si concentrations considerably exceed the C concentration [2].
References: [1] C. Hartmann, A. Dittmar, J. Wollweber, M. Bickermann, Semicond. Sci. Technol. 29 (2014) 084002 (10pp)] [2] K. Irmscher et al., J. Appl. Phys. 114, 123505 (2013).
S04-P26 Crystal growth of hexaferrits Z structure Ba(Sr)3 Co2 Fe24 O41 by floating zone melting.
A.M. Balbashov(1*, M.E. Voronchikhina(1, A.A. Mukhin(2, V.Yu. Ivanov(2, L.D. Iskhakova.(3 (1Moscow Power Engineering Institute,(Russia) (2A.M.Prokhorov General Physics Institute RAS,(Russia) (3Fiber Optics Center RAS(Russia) *email:[email protected]
Single crystals of hexaferrits with Z structure of Ba(Sr)3 Co2Fe24O41 are grown from the melt by zone melting method with light heating equipment URN-2-ZM. The accurate phase diagram of BaO(SrO)-MeO-Fe2O3 at high temperatures is unknown and the choice of growing conditions was based on data from the phase diagrams of BaO-Fe2O3 and SrO-Fe2O3. The structure of phase diagrams significantly depends on the partial pressure of oxygen above the melt. So crystal growth hexaferrits has been carried out in a closed crystallization chamber and pressure was maintain within 20-50 atm. Excess pressure of oxygen can lead to a change in valency of Co2 +, optimization technology on this parameter was controlled on the resulting electrical conductivity of the material. At low partial pressures of oxygen these compositions melt incongruently and the resulting single crystal contains numerous phase inclusions, but one phase with a hexagonal structure is prevailing. This confirmed according to the XRD and magnetic measurements. When the pressure of oxygen above the melt increases degree of incongruent melting of composition decreases, and at 30-50 atm. visually observed behavior of the melt zone testifies to the congruent character of the melting. As a result of sequential selection of modes of growth conditions parameters are found close to optimal for obtaining good quality of crystals: linear growth rate-4-5 mm/h, the speed of crystal rotationl-40 rpm, the speed of the feed rod 1-2 rpm., temperature of annealing furnace in crystal growth process -1000oC, partial oxygen pressure in crystallization chamber -30 atm. X-ray -phase analysis confirms the one phase structure of grown crystals. Strict maintaining the growth parameters during run is essential for obtaining single phase material. Failure of this to do so results in the arising of second phases, e.g. BaFe2O4, SrFe2O4. Feature of grown crystals of hexaferrits is that they are composed of plate blocks with a thickness of up to 1-2 mm. with hexagonal plane oriented along the axis of growth. Blocks can be disoriented relative to each other up to 1-2o. Electric resistivity of grown crystals is at level 107-108 Ohm.cm. Measurements of magnetization depending on temperature and magnetic field confirmed, basically, that the properties of grown hexaferrite single crystals of Z type correspond to the known parameters for these materials. Fig.1. show magnetization vs. magnetic field dependences for both compounds
80 4.2 K 4.2 K 100
70
80 H c 60 H c 290 K 290 K
50 H || c 60 H || c 40
30 40 Sr Co Fe O Ba3 Co2 Fe24O 41 3 2 24 41 growth 23.12.14 growth 11.02.15 Magnetization, emu/g Magnetization, emu/g
20 20
10
0 0 02040 02040 Magnetic field, kOe Magnetic field, kOe
. M ay 2015 May 2015
Fig.1. Magnetization vs. magnetic field of Ba3 Co2Fe24O 41 and Sr3 Co2Fe24O41 crystals.
S04-P27 Mathematical modeling of the process of growing a single crystal CdTe 100 mm by the Obreimov-Shubnikov method
Marina Pavlyuk*1, Ekaterina Sukhanova2, Marina Zykova2, Vladimir Kanevsky1, Igor Avetissov2
1A.V.Shubnikov Institute of Crystallography RAS, Leninskii pr. 59, Moscow, (Russian) 2D. Mendeleev University of Chemical Technology of Russia, Miusskaya pl. 9, Moscow, (Russia) *email: [email protected]
The growth kinetics is very important from the standpoint of improving of single crystal technology and understanding of optical and structural defects formation in the crystal during the growth process. A direct study of the kinetics of CdTe crystal growth is very difficult. Since the growing crystal is well shielded, the crystallization front (FC) in the melt and its visualization is not possible. Sometimes, in practice the FC in defective single crystals can be determined by decorating using microbubbles or by X-ray microanalysis, which allows displaying the components distribution along the growth axis and ingot diameter. These data could be applied to prove the results of numerical modeling of the growth process. The task of analysis of growth kinetics of large CdTe single crystals grown by the Obreimov-Shubnikov technique was solved by the numerical simulation using ANSYS 14.5 Fluent software. The calculation was carried out in three steps. At the first step we have calculated a thermal profile of an empty shaft furnace (Figure 1a). At the second step we simulated an internal space of the furnace with a quartz ampoule and a crucible with melt inside the ampoule (1b). At the final step we calculated the melt flows in the crucible using the thermal conditions obtained at the previous steps. The enthalpy model was used for crystallization simulation. The simulation results are consistent with the growth experiment results, confirming the adequacy of the numerical model. This work was supported by the Russian Foundation for Basic Research RFBR (grant №14-02-31726 mol_а).
a) b) Figure 1. Temperature distribution: a) thermal profile in the empty shaft furnace filled by air and b) thermal profile of the inner space of the furnace with the with a quartz ampoule and a crucible with melt inside the ampoule
S04-P28 Features compensate defects in CdTe using a stepwise cooling of the crystal
Marina Pavlyuk*1, Ilya Subbotin2, Vladimir Kanevsky1
1A.V.Shubnikov Institute of Crystallography RAS, Leninskii pr. 59, Moscow, (Russian) 2 National Research Centre "Kurchatov Institute", Akademika Kurchatova pl., 1, Moscow, (Russia) *email: [email protected]
The most important the aspect of application of CdTe is the production of detectors, X-ray and gamma radiation, which does not require additional cooling. High prices for any kind of CdTe crystals are caused due to a number of specific properties, difficulties in obtaining both large structurally perfect single crystals as well as the complexity of achieving high electrophysical parameters. The presence of phase transitions cause instability and non-reproducibility electrophysical properties of, which are highly dependent on the conditions in which the single crystal is grown. In this work presents the results to study of dependence of the microstructure CdTe single crystals grown by the Obreimov-Shubnikov method on the degree of doping of chlorine. Crystal growth occurred of the cadmium partial pressure PCd = 1 - 1.2 atm., which led to the achievement of the near-stoichiometric composition. Crystals were subjected to an improved post-cooling regime in view of the four-phase transitions [1]. The concentration of Cl introduced into the melt while growing the ingot was range from 1 · 1016 to 2 ·1019 cm-3. As a result, compensation growing crystals were characterized by p-type conductivity. From the phase diagram of the Cd-Te [1] follows that of repeated constriction solidus lines in the areas of phase transitions, getting free of Te precipitates crystals is very difficult and requires precise control of stoichiometry, or rather the composition of corresponding congruent phase transition Effectuation this requirement and at the same time with optimal conditions of doping and the use of improve the post-cooling regime obtained single crystals of CdTe free of Te precipitates , with a resistivity of > 109 Ωcm (remain unchanged for 10 years), dislocation density 1,25 · 104 cm-2 and transmittance 70% in the wavelength range of 1-25 µm.
References: [1] Ivanov Yu., J. of Inorg. Chem., 59 (2014) 1705–1714.
S04-P30 Investigations on synthesis, growth and physical properties of AgGaInS2 single crystals for Mid-IR application
N. Karunagaran* and P. Ramasamy
Centre for Crystal Growth, SSN College of Engineering, Kalavakkam 603110, India
*email:[email protected]
The I-III-VI2 ternary semiconductor of AgGaInS2 single crystal has been grown by Bridgman technique. Indium was partially substituted at Gallium site in chalcopyrite AgGaS2 structure. The growth of AgGaInS2 single crystal is done in two steps. First, synthesis of the polycrystalline material from the starting elements is achieved using melt temperature oscillation method. Secondly, the synthesized material is employed to grow a single crystal. AgGaInS2 crystallizes with chalcopyrite structure in the space group I-42d with unit cell parameters a = b = 5.831 Å, c = 10.876 Å. The synthesized AgGaInS2 polycrystalline charge was confirmed by powder XRD.
Thermal property of AgGaInS2 was analyzed using differential scanning calorimetry (DSC) technique. The melting point is 896°C and solidification temperature 862°C. The grown crystal was subjected to IR transmission. The transmission in the IR region is 65%. The band gap energy of the AgGaIns2 single crystal is 2 eV. The stoichiometric composition of AgGaInS2 single crystal was confirmed using energy dispersive spectrometry (EDS).
Figure 1. Single crystal ingots of AgGaInS2
S04-P31 Crystal Growth and Thermoelectric Properties of Sr2Fe2O5 Single Crystals
Hossain Md Anwar1,2*, Mori Takao2, Nagao Masanori1, Watauchi Satoshi 1 and Tanaka Isao1
1Center for Crystal Science and Technology, University of Yamanashi, Miyamae 7-32, Kofu, Yamanashi 400-8511, Japan 2 National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba 305-0044, Japan *email:[email protected]
SrFeO3- with a wide oxygen non-stoichiometry is interesting material as mixed oxide-ionic and electron conductor at elevated temperatures. Some oxides of the brownmillerite structure with an oxygen deficient perovskite exhibit high oxide ion mobility. At temperature below 850 ºC the reduced ferrite SrFeO2.5 is stabilized to the orthorhombic brownmillerite (OB) structure Sr2Fe2O5 where vacancy ordering results in an alternation of layers of octahedral FeO6/2 (O) and tetrahedral FeO4/2 (T) along the b-axis. We reported here the floating zone growth and characterization of Sr2Fe2O5 single crystals. The SrFeO3- crystals grown in O2 atmosphere were severely cracked at room temperature. This cracking into the SrFeO3- crystals due to the phase transition from brownmillerite ( =0.5) to the orthorhombic (=0.25) phase by the oxidation of Fe3+ ions to Fe4+ ions during cooling after growth in O2 atmosphere. The dominant oxygen diffusion mechanism through such a crystal is via microcracks rather than oxygen vacancies, while the same cracks complicate the interpretation of transport measurements. For the low temperature transport properties and intrinsic oxygen diffusion 3+ the cracking should be minimized. To prevent the oxidation of Fe ions in SrFeO3- we tried to grow SrFeO3-single crystals in Ar atmosphere. The crystals grown in Ar atmosphere were crack free and twinned structure. The SrFeO3- crystals grown in Ar atmosphere were identified to be brownmillarite type structure ( =0.5) by powder XRD.
We also studied the thermoelectric properties of Sr2Fe2O5 single crystals to check the possibility of the materials in thermoelectric applications. Resistivity and Seebeck coefficient of the grown crystals were measured with an ULVAC ZEM-2 in the temperature range of 200–800 ºC in He atmosphere. Power factor was calculated from the resistivity and thermoelectric power values. The maximum power factor (13 Wm-1K-2) was obtained at 800 ºC. In order to obtain an idea of the thermoelectric performance, thermal conductivity was measured for the crystals with suitable dimensions. To determine the thermal conductivity values within the same temperature range 50- 800 ºC, the specific heat and thermal diffusivity coefficient of the crystals were measured by using DSC-8231 (Differential Scanning Callorimetry) and a laser flash method (ULVAC TC-7000), respectively. The thermal conductivity of the grown crystals was determined to be 3.6 Wm-1K-1at 800 ºC. Due to high thermal conductivity ZT value became low (0.004). If it is possible to increase electrical conductivity and reduce thermal conductivity by doping with suitable element, this material could be a promising thermoelectric material.
Figure 1: Sr2Fe2O5 single crystal grown by floating zone method
S04-P33 Magnetocaloric and Hopkinson effects in slowly and rapidly cooled Gd7Pd3
Oboz Monika*1, Talik Ewa1, Guzik Adam1, Zajdel Paweł1, Grzegorz Ziółkowski1
1Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice (Poland) *email: [email protected]
Investigations of X-ray diffraction, dc and ac-magnetic susceptibility, magnetocaloric properties and scanning electron microscopy (SEM/EDX) in order to elucidate the Hopkinson and magnetocaloric effects in relation to the technological aspects for slowly cooled polycrystal and rapidly cooled (rc) casts of Gd7Pd3 intermetallic compound were performed. The slowly cooled polycrystalline samples were obtained by melt in an induction coil. The rc-cast Gd7Pd3 sample was obtained by means of a mould casting technique. The obtained Gd7Pd3 samples crystallized in a Th7Fe3-type hexagonal phase with space group P63mc. The gadolinium atoms in this type of structure occupy three non-equivalent crystallographic positions (2b and 6c sites) and the Pd atoms only one (6c position). Moreover, in the the Gd ions are located in the triangular configuration. Monocrystalline Gd7Pd3 orders ferromagnetically below 334 K, polycrystal and powdered rc- cast Gd7Pd3 undergo magnetic transformation at 332 K and 331 K, respectively, while the bulk rc- cast Gd7Pd3 orders ferromagneticalli below 339 K. The SEM/EDX elemental analysis showed that the sample was homogeneous and the stoichiometry was in agreement with the nominal one. Figure 1a shows a surface of the rc-cast material. Figure 1b shows a crystal which grew on the fringe of the rc-cast sample. The crystal habit is in agreement with the hexagonal crystal structure of the compound. The size of the crystal is of the order of several micrometers. The calculated entropy changes ΔSm at 7 and 2 Tesla were -6.6 J/Kkg and -2.8 J/Kkg for the Gd7Pd3 single crystal, -6.73 J/Kkg and -2.72 J/Kkg for polycrystal, -6.03 J/Kkg and -2.52 J/Kkg for the rc-cast Gd7Pd3, -5.11 J/Kkg and -2.01 J/Kkg for rc-powdered samples, respectively. The investigated ferromagnetic system is sensitive to grain size. The magnetocaloric effect and Hopkinson peak decreases with the decrease of the grain size. The results were compared to the data of single crystal obtained for grown by the Czochralski method from a levitating melt.
a) b) Figure 1. SEM images of rc-cast Gd7Pd3: a) a side view of the mould (magnification 40x), b) the twin crystal of the compound on the surface of the mould (magnification 1800x) Acknowledgements This work was partially financed by the Polish National Science Centre (Narodowe Centrum Nauki) under Grant No. 2011/03/B/ST5/01035.
S04-P34 Characterization of CSBN single crystals by XRF, XRD, SEM, XPS and electrical conductivity studies
Szubka Magdalena*1, Talik Ewa1, Kusz Joachim1, Duda Henryk1, Świrkowicz Marek 2, Winiarski Antoni1, Kisielewski Jarosław2
1A. Chełkowski Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, Poland 2 Institute of Electronic Materials Technology, Wólczyńska 133, 01-919 Warsaw, Poland *email: [email protected]
The crystals of ferroelectric niobates with the structure of tungsten bronze such as SrxBa1- xNb2O6 (SBN) and CaxBa1-xNb2O6 (CBN) are the subject of intense investigations in the view of their very interesting non-linear electro-optical, dielectric, piezoelectric and pyroelectric properties. Doping with rare earth ions additionally increases the possibility of using these crystals in laser technology. The growth of crystals being the mixture of SBN and CBN had been also undertaken in order to obtain materials with intermediate values of the Curie temperature. Single crystals of ferroelectric CaxSryBa1-x-yNb2O6 (CSBN) were obtained by the Czochralski method. Thermal system with platinum crucible and blowing of air at its bottom to change temperature distribution in the melt (crucible base cooling) was used. The charge material was prepared as a mixture of two compounds CBN and SBN with compositions which melt congruently. The main formula of charge was: xCBN + (1-x)SBN. Single crystals were grown for the following compositions: x = 0.25; 0.50 and 0.75. In case of compositions x = 0.50 and 0.75 single crystals were also doped with neodymium. Single crystals up to 24 mm in diameter and 60 mm in length with characteristic 24 faces were grown. The aim of this work was determination of the chemical composition, electronic structure and electrical conductivity examination of CSBN single crystals cut out respectively along (001) and (100) planes. High-resolution core level spectra of the Ca 2p, Sr 3d, Nb 3d, Ba 3d, O 1s states show that the bulk of the CSBN crystals is characterized by only one chemical state for each element, which dominates in the structure. The difference in chemical composition in relation to nominal value obtained from XPS, XRF and SEM analysis may result in appearance of oxygen vacancies and some defects in the CSBN crystals. It can be reflected by electrical conductivity studies. The order of magnitude of measured conductivity is very small. Depending on the crystallographic direction the conductivity is anisotropic but in the case of measures in both directions the conductivity characteristic changes in the same temperature from semiconductor to similar to metallic. For both directions the activation energy is essentially the same. In lower temperatures one man can observe the increase of conductivity, where the source of carriers could be probably the defects in examined crystals. In the temperature near 370 K conductivity begins to decrease, what can be related to the increase of scattering on crystalline network vibrations.
Figure 1. Photos of CSBN75 single crystals
S04-P35 Influence of growth parameters on electrical proprieties of highly polluted mc-Si grown by the Bridgman technique with various crucible-coating combinations
Negrila Radu Andrei*1, Pupazan Vasile1, Vizman Daniel1
1Faculty of Physics, West University of Timisoara, Bd. V. Parvan 4, 300223, Timisoara, Romania *email: [email protected]
In the race to improve the price of solar energy by lowering the costs for silicon solar panel production, one of the important production segments to be addressed are the purification and crystallization of photovoltaic grade silicon. Currently, directionally solidified multi-crystalline silicon (mc-Si) is predominant in the market of photovoltaic silicon (2015: ~65% [1]) and is expected to stay so during the following decade. Because of its low costs and its similarities with directional solidification, Bridgman growth of small diameter (max. 3 cm) mc-Si is a suitable technique for a fundamental study of the influence of growth parameters (like growth rate and process time, temperature gradients, crucible coating) on the interface shape, grains size and impurity distribution and precipitation, which are important parameters for the photovoltaic applications. As silicon is crystallized in non-reusable silica crucibles with anti-sticking silicon nitride coatings, experimental investigations have been performed on new different crucible-coating combinations for the identification of cheaper and maybe even reusable crucible materials. Even though an electronic grade quality Silicon feedstock was employed, a large distribution of impurity precipitates (especially of SiC) was found in most growth experiments. A very high neutral impurity (C and O) concentration has been found. These impurities have largely entered the molten silicon through diffusion into the liquid phase, aided by convective transport [2]. Therefore the impurity concentration in the melt is strongly related with the time duration in which the silicon was in the molten phase, but also to the different coating materials that were employed. In this work, this behavior is linked with the increasing average resistivity values and decreasing minority carrier lifetime. While decreasing lifetime with increasing impurity concentration is a standard prediction of the SRH electron-hole recombination model, the resistivity increase is explained by majority carrier mobility limitation through scattering on neutral impurity centers (C and O) for unusually high impurity concentrations (>1017 at/cm3) [3]. It seems that, for highly polluted mc-Si majority carriers, scattering on neutral impurities mechanism prevails in limiting the carrier mobility over scattering on ionized dopants and phonons. Therefore, the distribution of neutral impurities can be directly linked to resistivity scans for highly polluted mc-Si through their modulation of the value of carrier mobility in areas with different impurity concentrations. Since the impurity distribution is dependent on the convection structure, this observation could be implemented for the experimental tracing of the convection during growth in a DS furnace of much larger dimensions.
References: [1] Semiconductor Equipment and Materials International (SEMI), International Technology Roadmap for Photovoltaic (ITRPV) 2014 Results (April 2015). [2] Popescu A., Vizman D., International Journal of Heat and Mass Transfer, 54 (2011), 5540. [3] Kireev P. S., Semiconductor Physics, Mir Publishers (1978).
S04-P40 2+ Optical properties of Cd1-xMnxTe:Fe crystals
O.K.Kapustnyk1*, N.O.Kovalenko1, I.S.Terzin1, P.V.Mateychenko1, D.S.Sofronov2, A.G.Fedorov3
1Institute for Single Crystals of NAS of Ukraine, Lenina Ave. 60,Kharkiv (Ukraine) 2 STC "Institute for Single Crystals" of NAS of Ukraine, Lenina Ave. 60,Kharkiv (Ukraine) 3 Institute for Scintillation Materials of NAS of Ukraine, Lenina Ave. 60, Kharkiv (Ukraine)
*email: [email protected]
Lasing range expansion is one of the main tasks of laser materials science. For chalcogenide active media it can be solved by creating a new hosts based on the solid solutions of chalcogenides. Analysis of the existing literature [1-4] shows that the most promising material for shifting of the lasing band toward longer wavelengths is Cd1-хMnхTe. Currently, the literature describes the 2+ optical properties of a solid solution of Cd1-хMnхTe:Fe with the only one value of the manganese concentration x = 0.45 [4]. The article shows the potential of the given material for the lasing band shifting to longer wavelengths of the optical spectrum. However, the studies were carried out for one solid solution composition only. Thus, great interest is to obtain a series of solid solutions 2+ Cd1-хMnхTe:Fe and to study their optical properties to obtain an understanding of the relationship between the structural parameters of the crystalline host and optical properties of the active ion. 2+ Crystals of a solid solution Cd1-хMnхTe:Fe were grown by the Bridgman method under overpressure of an inert gas. Optical spectrophotometry for visible, near and mid-infrared regions was performed by a spectrophotometer PerkinElmer Lambda 35 and PerkinElmer Spectrum One. The elemental composition of the obtained samples was defined by an electron microscope with the energy dispersive microanalysis system. XRD analysis has been used for investigation of structural properties. 2+ The series of the solid solution Cd1-хMnхTe:Fe crystals for the concentration range x between 0.09 to 0.52 was grown. Absorption spectra in the mid-IR and visible ranges of the optical spectrum are studied. The correlation between the solid solution Cd1-хMnхTe composition, structural properties and the maxima positions of the Jahn-Teller components of the Fe2+ ions absorption cross section was shown. Obtained results can be used for prediction of possible lasing range for CdMnTe:Fe2+ active media.
References: [1] V.V. Fedorov, W. Mallory, S.B. Mirov, U. Hömmerich, S.B. Trivedi, W. Palosz, “Iron-doped CdxMn1−xTe crystals for mid-IR room-temperature lasers”, Journal of Crystal Growth, V. 310, Issue 20, 1 October 2008, Pages 4438–4442. [2] M. Mond, D. Albrecht, E. Heumann, G. Huber, S. Kück, V. I. Levchenko, V. N. Yakimovich, V. G. Shcherbitsky, V. E. Kisel, N. V. Kuleshov, M. Rattunde, J. Schmitz, R. Kiefer, and J. Wagner, "1.9- μm and 2.0- μm laser diode pumping of Cr2+:ZnSe and Cr2+:CdMnTe," Opt. Lett. 27, 1034-1036 (2002). [3] A.V Podlipensky, V.G Shcherbitsky, M.I Demchuk, N.V Kuleshov, V.I Levchenko, V.N Yakimovich, S Girard, R 2+ Moncorgé, “Cr :Cd0.55Mn0.45Te crystal as a new saturable absorber for 2 μm lasers”, Optics Communications, Volume 192, Issues 1–2, 15 May 2001, Pages 65–68. [4] S. B. Trivedi, C.C.Wang, S. Kutcher, U. Hommerich, W. Palosz, “Crystal Growth Technology of Binary and Ternary II-VI Semiconductors for Photonic Applications”, Journal of Crystal Growth, 310, 2008, 1099-1106.
S04-P41 Growth of Bi2Te3, Cr2Ge2Te6 and CrSi2Te6 crystals for Topological Interests
C.Bagavath1*,R.MohanKumar1,T.Shalini1,J. Kumar1, C. Ferrari2, L. Nasi2, L. Lazzarini2
1Crystal Growth Centre, Anna University, Chennai – 600025INDIA. 2IMEM-CNR Institute, Parco Area delle Scienze 37/A Parma – 43124, Italy *e-mail :[email protected], [email protected]
In recent years, topological insulators are considered to be a hot research topic in condensed matter physics, motivating further development of the concept of topology in materials studies. Bismuth Telluride (Bi2Te3) is a narrow gap layered semiconductor with a hexagonal (or rhombohedral) close-packed structure. Bi2Te3 has a direct band gap of 0.21eV and it possesses high anisotropic electrical and thermal conductivity. When alloyed with antimony or selenium, it acts as an efficient thermoelectric material for refrigeration or portable power generation. In addition to its role as a thermoelectric material, bismuth telluride is also one of the most commonly studied topological insulators (TIs) to date.
In our present study, single crystals of Bi2Te3 have been grown by Chemical Vapor Transport (CVT) method. Stoichiometric amounts of high purity bismuth and tellurium were taken in a quartz ampoule, sealed and kept at 773 K for 8 hours. The synthesized material was ground into a fine powder and was taken in a fresh quartz ampoule with Iodine as the transporting agent and was sealed. By using a two zone horizontal resistive heating furnace, the source and growth temperature was maintained at 823 K and 698 K respectively. The source and growth zone temperatures were changed in order to achieve good nucleation and they were maintained at a constant temperature for 15 days to obtain good quality single crystals of Bi2Te3.
Cr2Ge2Te6 is particularly interesting since it is in the very rare class of ferromagnetic insulators, and possesses a layered, nearly two dimensional structure. Recently, this material has been revisited due to its small lattice mismatch with the topological insulator Bi2Te3, making it an ideal candidate as a substrate for devices. In the present study, Cr2Ge2Te6 and CrSi2Te6 single crystals were grown by self- flux Bridgman method. High purity powders of Cr,Ge,Te were mixed in the molar ratio of 1:1:6 with excess of 20% Te which acts as a flux. Similarly, Cr,Si,Te powders were mixed in the molar ratio of 1:2:6.The mixture is heated to 1273 K for 8 days and later annealed at 973 K under argon atmosphere in order to remove the excess Te. Structural investigations using X-ray diffraction and Raman confirmed the crystallinity of rhombohedral Cr2Ge2Te6 and CrSi2Te6 single crystals. The SEM images shows step like growth features. AFM and MFM studies were also done and the details will be presented.
S04-P42 Characterization of G2-sized quasi-mono Si directionally solidified in TMF
Frank M. Kiessling2,*, Natasha Dropka1, Christiane Frank-Rotsch1, Torunn Ervik1, Dieter Linke1, Robert Menzel1, Thomas Richter2, Lamine Sylla2
1 Leibniz-Institut für Kristallzüchtung (IKZ), Max-Born-Str. 2, D-12489 Berlin (Germany) 2 SolarWorld Innovations GmbH, Berthelsdorfer Straße 111 A, 09599 Freiberg/Sachsen (Germany) The motivation for improving the performance of solar cells is high, as this leads to a significant cost reduction in terms of price/Wp. Directional solidification (DS) is the standard process for large-scale production of multi-crystalline Si ingots for Si-based solar cells. A strong focus towards higher efficiencies by reducing lifetime limiting defects forces manufacturers to develop new growth technologies. The last few years have seen several new approaches, which aim to eliminate or mitigate the defect density in DS-Si. One of these approaches is the growth of quasi-mono ingots using seeds on the bottom of the crucible. In addition to the challenging growth process, multiple seeds are needed. It is essential to control defects from the seed junctions [1] as well as those formed at the crucible walls. Grains and their boundaries are known to be major sources for the development of unfavorable recombination active dislocation clusters. In order to study the influence of travelling magnetic fields (TMFs) on the growth conditions and, hence, the defect development, quasi-mono silicon ingots have been directionally solidified in a vertical gradient freeze-type furnace equipped with KRISTMAG-heaters [2]. As-grown G2-sized silicon ingots of 38 x 38 x 23 cm3 in volume were cut vertically and their defect structure was analysed. Information was obtained on the curvature of the solid-liquid interface, the grains nucleated at the crucible walls and the electrical activity of dislocations. A main focus of this investigation was the control of dislocation formation, which can easily originate from the seed junction (see Fig. 1a and 1b).
a) b) Figure1 a) Bottow view on the as grown ingot showing the fully geometry of the used seed. b) Photoluminescence image of a vertical cut. No dislocation cascade is observed in the middle, which are known to originate from the junction between the two seeds.
References: [1] M.G. Tsoutsouva,V.A. Oliveira, D. Camel, J. Baruchel, B. Marie, and T.A. Lafford, Acta Materialia 88 (2015) 112-120. [2] D. Linke, N. Dropka, F.M. Kiessling, M. König, J. Krause, R.-P. Lange, D. Sontag, Solar Energy Materials and Solar Cells 130 (2014) 652-660.
* Corresponding author, phone / fax: ++ 49 (30) 63 92 30 33 / 30 03, E‐mail: frank.kiessling@ikz‐berlin.de
S04-P43 β-Ga2O3 Crystals Grown from Al2O3-Ga2O3 Melt
Nikolaev Vladimir1,2,3, Maslov Viktor1,2*, Krymov Vladimir 1,2, Kalashnikov Evgenij4, Romanov Alexey1,2
1 Ioffe Physical Technical Institute, 26 Politekhnicheskaya str., Saint Petersburg, 194021 Russia 2ITMO University, 49 Kronverkskiy prospect, Saint Petersburg, 197101, Russia 3 Perfect Crystals LLC, 28 Politekhnicheskaya str., Saint Petersburg, 194064 Russia 4MGOU, Radio str., 10, Moscow, 105005, Russia.
e-mail: [email protected]
Tabular β-Ga2O3 single crystals (Fig.1) were grown by free crystallization from Ga2O3 -Al2O3 melt in sapphire crucible [1]. Growth mechanisms and properties of the crystals have been studied; main features of optical and mechanical behavior of the crystals have been revealed. It was shown some cleavage planes in the crystals; parallel to the pinacoid and monohedron planes are perfect; parallel to the planes of the rhombic prisms are imperfect. The crystals had block structure and some pores with diameter from 0,01 to 0,5 mm. The total content of Al in grown crystals was about 5 at. %. The cleaved crystal plates have been successfully tested for gas transport epitaxial growth of nitride semiconductor films [2].
Figure 1. Single crystal β-Ga2O3 plate
References: [1] V.N. Maslov, V.M. Krymov, M.N. Blashenkov, A. A. Golovatenko, V.I. Nikolaev, Tech. Phys. Lett. 40 (2014) 303–305 [2] V.I. Nikolaev, A.I. Pechnikov, V.N. Maslov, A.A. Golovatenko, V.M. Krymov, S.I. Stepanov, V.E. Bougrov, A.E.Romanov GaN growth on β-Ga2 O3 substrates by HVPE, Materials Phys. and Mechanics 22 (2015) 59–63.
S04-P44 Growth, structural and magnetic characterization of highly ordered Co2FeSi single crystals
R. Mohankumar*1, M. Manivel Raja2, S. Ganesamoorthy3, J. Kumar*1, C. Ferrari4, L. Nasi4, L. Lazzarini4
1 Crystal Growth Centre, Anna University, Chennai – 600 025, India. 2 Defence Metallurgical Research Laboratory, Hyderabad – 500 058, India. 3 Material Science Group, IGCAR, Kalpakkam – 603102, India. 4IMEM-CNR Institute, Parco Area delle Scienze 37/A Parma – 43124, Italy. *email :[email protected], [email protected]
Half metallic ferromagnets are expected to make spintronic devices such as magnetic tunnel junctions (MTJ) and spin injectors, due to their high spin polarized current to semiconductors [1]. Among the Half metallic ferromagnets Heusler type Co2FeSi crystallizes in L21 structure and has received considerable attention due to its high Curie temperature (1100 K), complete spin polarization and high magnetic moment (5.97 µB) [2]. Alloying of ternary intermetallics always ends up with several disorders (A2 type, B2 Type and Do3 type) and this shows challenges to separate its intrinsic and extrinsic properties. Hence, the growth and characterization of high quality single crystals are required to get more information on its intrinsic properties. Co2FeSi single crystals are grown using four mirror optical floating zone technique under Ar atmosphere. High pure arc melted polycrystalline Co2FeSi alloy was used for seed and feed rod preparation. The presence of L21 ordering in grown single crystalline Co2FeSi was confirmed using X-Ray Diffraction and Mössbauer spectroscopic measurements. The measured magnetic moment agrees well with that of the magnetic moment calculated using DFT calculations [3].
References: [1] Felser C., Fecher G. H., Spintronics: From Materials to Devices, Springer, Berlin (2012). [2] Wurmehl S., Fecher G. H., Kandpal H. C., Ksenofontov V., Felser C., Phy Rev B, 72 (2005) 184434. [3] Mohankumar R., Ramasubramaniyan S., Rajagopalan M., Manivel Raja M., Kamat S. V., Kumar J., J. Mater. Sci, 50 (2015) 1287.
S04-P45 Effect of crucible geometry and fixed heat exchangers in the solid-liquid interface for growing CdZnTe bulk crystals using a Vertical Gradient Freeze technique
REPISO Eva 1, CORROCHANO Alvaro1, RUBIO Sandra1, PLAZA Jose Luis1, TSYBRII Zinoviia2, VUICHYK Mykola2, DIEGUEZ Ernesto1*
1Depart. Physics of Materials, Universidad Autónoma de Madrid (UAM), Madrid (Spain) 2Institute of Semiconductor Physics (ISP), Kiev (Ukraine) *email: [email protected]
CdTe alloy materials are extensively used on security and medical applications as bulk materials, in particular CdZnTe (Zn=4%) (CZT) could be the key for achieving the realization of drugs and explosive detectors [1]. This material presents many difficulties in the bulk growth to get large size, free from defects and homogenous dopant material along the whole ingot; but the crucible shape and the heat exchange have been considered as key parameters that considerably influence the material quality [2]. On the other hand, the simulations carried out in the frame of the crystal growth processes have revealed to give very helpful approaches for improving the materials quality, giving clear indications of the best experimental results [3]. In this work, the commercial CrysMAS code has been used in order to select the best growth conditions in the case of bulk CZT crystals by the Vertical Gradient Freeze (VGF) technique. The boundary conditions have been chosen from the geometry of the VGF equipment available in the laboratory, which is normally applied for growing two inches CZT diameter crystals, together with the real temperature gradients from a real CZT bulk growth. Different PBN crucible with quartz envelopes geometries such as flat, conical and seeded bottom shaped have been simulated, with and without the attachment of a heat exchanger system, considering the growth rate and the shape of the solid-liquid interface as the critical parameters for selection of the preferential geometry. It has been found that the conical shape provides no significant benefits over the flat one, owing that a convex interface is never obtained when the shape of the crucible is constant. Otherwise the implementation of a hollow cylinder of Pt, W, PBN and SiC has been analyzed with the objective of improving the solid-liquid interface. The results of the simulation when a W hollow cylinder is used as heat exchanger in a flat crucible bottom shows an improvement in the shape of the solid liquid interface with a slightly convex interface shape along the half part of the growth ingot, a situation which is more complex when other bottom shaped conical crucible are used. Results related with the seeded bottom crucible together with the possibility of a movable heat exchanger will be discussed.
References: [1] M. C. Kemp, IEEE 1, 1 (2011) 282-292 [2] V. Carcelén, N. Vijayan, E. Dieguez, A. Zappettini, M. Zha, L. Sylla, A. Fauler and M. Fiederle, Journal of Optoelectronics and Advanced Materials, 10 11 (2008) 3135-3140 [3] N. Zhang, H. G. Park, J. J. Derby, Journal of Crystal Growth, 367 (2013) 27-34
S04-P47 High purity Germanium Crystal Growth
Aravazhi Shanmugam
Umicore Electro-Optic Materials Watertorenstraat 33 B-2250, Olen Belgium Email : [email protected]
High purity germanium crystals (HPGe) are excellent candidates for high resolution gamma ray detection and recently for dark matter research (WIMP). In this regard, worldwide attention has been focused on fulfilling the crystal growth needs of high quality HPGe crystals of increasing size and narrow purity range. Unlike standard Czochralski germanium crystal growth that focuses on the dislocation free nature of crystals with excellent dopant control; the prerequisite for HPGe growth are (1) an ultra clean crystal growth process such that extremely stringent purity levels can be reached and (2) a special crystal growth control in order to meet the specific crystalline quality and boule size. Since the early 50’s, UM-EOM started with the production of high quality germanium crystals for a wide range of applications : electronic, micro-electronic, infrared and high purity Ge. Over the past decades, Umicore Electro-Optic Materials (UM-EOM) has established itself as a world leader in most of these fields. During the presentation, an overview of the crystal growth capabilities of HPGe at UM-EOM will be given. The importance of various crystal specifications, growth methods and characterization methods will be discussed. This work forms a basis for the successful production of high quality HPGe crystals to meet the ever more stringent specifications, like increased boule size and reduced impurity range.
Key Words: Germanium, crystal growth, high purity materials, gamma ray detection, dark matter
S04-P48 The influence of finite silicon electrical conductivity on melt flow and dopant transport in floating zone crystal growth process
Kirils Surovovs*1, Andrejs Sabanskis1, Janis Virbulis1
1University of Latvia, Zellu street 8, LV-1002, Riga (Latvia) *email: [email protected]
Present work is devoted to the numerical modelling of silicon single crystal growth with floating zone (FZ) method (Figure 1.a). A 4 inch system from Institute for Crystal Growth, Berlin is used [1]. Specific attention is paid to calculation of electromagnetic (EM) field in the vicinity of external triple point, where the previously used high-frequency approximation with surface currents is less precise due to significant difference between conductivities of solid and liquid silicon. Local 2D (in Figure 1.b heat source density Q is shown) and 3D volumetric calculations of EM field in the vicinity of external triple point showed significantly more power in melt and less – in crystal. Calculated redistribution of electric current is parameterized and used in more precise simulations of interface shapes and melt flow. Melt flow and dopant transport are calculated using FZSiFOAM program, which is based on OpenFOAM code library. It calculates non-stationary melt flow, temperature and dopant concentration. A sample of obtained temperature field is shown in Figure 1.c. To describe induced heat sources and Lorentz force more precisely, changes in the boundary conditions of existing programs are applied. Modifications are verified by comparing calculated radial electrical resistivity distributions with experiments for various crystal pulling rates (see Figure 1.d and 1.e for radial resistivity profiles). It was shown that concentration boundary conditions on the free melt surface are more important than the precise description of local EM field near the external triple point.
Figure 1. a) Overall scheme of FZ system; b) Heat source density in silicon from 2D EM calculations; c)Temperature field from 3D melt flow calculations; d) Radial resistivity distribution in obtained crystal for different crystal pulling velocities; e) Average crystal resistivity (solid lines) and deflection of the resistivity profile (dashed lines) for different crystal pulling velocities.
References: [1] R. Menzel., “Growth conditions for large diameter FZ Si single crystals”, Ph. D. Thesis, Technischen Universität Berlin, 2013.
S04-P49 3D simulation of feed rod melting in floating zone silicon single crystal growth
Plāte Matīss*1, Krauze Armands1,Virbulis Jānis1
1Faculty of Physics and Mathematics, University of Latvia, Zeļļu 8, Rīga, Latvia *[email protected]
A three dimensional (3D) transient model of the feed rod melting in the floating zone (FZ) silicon single crystal growth process is presented. The system geometry [1] and process parameters from a converged state of quasi-stationary axisymmetric calculations of global heat transfer and phase boundaries are used as initial condition for the time dependent simulations. Introduction to the considered FZ process is given in Fig. 1. Transient models of the 3D heat conduction, high- frequency electromagnetic field and the fluid film [2] are coupled to obtain the local melting rate on the open melting front. The calculations show that the inductor slit configuration determines the melting rate distribution, and the azimuthal profile of the feed rod rim stabilizes in few rotation periods, see Fig. 2. A study of varied feed rod and inductor parameters is carried out. Although the absolute changes of feed rod profile shape do not exceed 1 mm for the investigated parameter range, these differences are crucial when comparing the simulations with experimental data.
Feed rod
Inductor Melt
Crystal
A B C
Figure 1. Introduction to the considered FZ process. Panel A: 3D model of the 4” FZ system. Panel B: discretization of the feed rod domain with finite element mesh used to obtain the initial state (left) and finite volume mesh for the transient heat transfer calculations (right). Panel C: temperature field and the modelled surfaces given as 1 – melting interface, 2 – open melting front and 3 – feed rod side surface.
vm, mm/min
Figure 2. Left: distribution of the local melting rate on the open melting front of a converged state. Right: azimuthal profile of the feed rod rim at various time instants during the transient simulation. References: [1] Rost H.-J., Menzel R., Luedge A., Riemann H. Journal of Crystal Growth, 360 (2012) pp. 43 – 46 [2] Ratnieks G., Muiznieks A., Muhlbauer A., Journal of Crystal Growth, 255 (2003) pp. 227 – 240
S04-P50 Crystal growth and characterization of an oxy-fluoride crystal (BaCaBO3F) doped with Yb3 ions for self-frequency doubling: a thrilling challenge
Federico Khaled1, Suchinda Sattayaporn1, Pascal Loiseau1, Gérard Aka1, and Lucian Gheorghe2
1PSL Research University, Chimie ParisTech – CNRS, Institut de Recherche de Chimie Paris, 75005 Paris, France 2 National Institute for Laser, Plasma and Radiation Physics - LSSQE, Bucharest Romania *email: [email protected]
Self-frequency doubling crystals are very promising materials because they allow efficient emission in the visible range from high-efficient frequency conversion of the solid-state infrared laser emissions, while being very compact. We will present the crystal growth and the potential as SFD candidate of an oxy-fluoride crystal that can be obtained by the Czochralski method: Yb:BaCaBO3F (YB:BCBF). This compound presents a congruent melting behavior at 1100°C. Based on ionic radii, Yb3+ luminescent ions are assumed to substitute for Ca2+ ions. Therefore, two different mechanisms for charge compensation might occur: cationic co-doping with Na+ in the 2+ Ca site, leading to BaCa1-2xYbxNaxBO3F, or anionic replacement of fluoride by oxygen, leading to BaCa1-xYbxBO3(F1-xOx). The atmosphere (N2) and the nature of the crucible (Pt) were optimized for the growth of the un-doped material. According to crystal growth experiments (Fig 1), the first mechanism seems to be the most favorable towards getting good optical quality crystals. Even though only one insertion site for rare-earth ions was assumed, low-temperature absorption and EPR spectra tend to indicate multiple environments for the Yb3+ ions. Along with that, the segregation coefficient of Yb3+ was found to be close to 3 (measurements done by ICP- AES and EDX), while the one for Na+ charge compensating ions is lower than unity. All this leads to some naked eye defects (precipitate phases and scattering centers), lowering the crystal quality compared to the un-doped material. Also, the replacement of some Ba2+ by Sr2+ was attempted to improve the mechanical properties. By the way, better crystal quality with less naked eyed defects was observed. Recently, the author of [1] assumed a reversible phase transition from space group R3to space 3- group P-62m at 242°C in the undoped material, linked to the rearrangement of some (BO3) groups in the (ab) plane. However XRD experiments on samples with more than 1%at Yb3+ do not present the R3 superstructure peaks at room temperature. Moreover, Raman analysis on samples with different Yb3+ concentration indicates a different behavior. Two hypotheses can be made: either the ytterbium helps to stabilize the P-62m structure at room temperature, either ytterbium ions create disorder leading to a more symmetric apparent structure. The inhomogeneous ytterbium concentration along the crystal is not convenient for obtaining optical and laser applications. Therefore, the key issue for using Yb:BCBF as a SFD crystal remains the crystal growth. Crystal growth experiments, along with spectral properties and early infrared laser operation will be presented.
Fig 1. BCBF crystals doped with Yb3+ (left), co-doped Yb3+/ Na+ (middle) and co-doped Yb3+/ Na+/ Sr2+ (right) References: [1] R.K. Li et al., J. Cryst. Growth, 382 (2013), pp 47-51.
S04-P51 Ge-containing Quartz Single Crystals - New Advanced Piezoelectric Material
Balitsky S.Vladimir*1, Balitsky V. Denis2, Balitskaya V. Liudmila1, Setkova V. Tatiana1, Nekrasov N. Aleksey1
1 Institute of Experimental Mineralogy RAS, Acad.Osipian 4, Chernogolovka (Russia) 2 Baccarat (France) *email: [email protected]
This work describes some problems of crystal growth and main properties of Ge-containing α- quartz a new piezoelectric monocrystalline material. Natural and synthetic quartz are used widely in piezoengineering, acoustoelectronics, optics and other fields of science and technics for many years. Piezoelectric constants as well electromechanical coupling coefficient of quartz are lower than for other piezoelectric (germanium dioxide, gallium orthophosphate, berlinite, langasites et al.), but the quality factor is higher. The performance of piezoelectric quartz elements is limited by temperature of 280–290°С because of proximity of phase transformation and as a result: frequency drift is observed. That is why, a development of new more effective piezoelectric materials, which have relatively high quality factor and in the same time work at high temperatures (400–800°С) is actual. In last 15 years, the gallium orthophosphate (α-GaPO4) and some langasites were more perspective single crystal materials. However, growth of large and perfect crystals involves a lot of technical difficulties as for example for GaPO4: absence of large and quality seeds and twins. From other hand, the langasites are very inhomogeneous because of complex composition, so the quality factor is low. This work shows scientific substantiates of reliable laboratory method of single crystal s growth of Ge-containing quartz based on study of morphology of crystals, internal structure and determination of piezoelectric properties. The quite perfect single crystals of Ge-containing quartz with content of GeO2 12-14 wt. % were grown in aqueous fluoride fluids at temperatures of 500- 600°C and pressures of 70-150 MPa. Piezoelectric characteristics of the as-grown crystals are near to gallium orthophosphate, α → β transition is increased to 840°C and it rises more at increasing of germanium content. The elements prepared from germanium quartz are greatly increase the temperature limits of equipment operability. The electromechanical coupling coefficient of Ge- containing quartz is also near to gallium orthophosphate. Dielectric loss tangent of Ge-containing quartz single crystals in two to three orders of magnitude lower than that of natural and standard synthetic quartz. Thus, the experimental results allow consider single crystals of high germanium quartz as promising piezoelectric material which is suitable for many traditional piezoelectric applications and in new high performant engines as a component of combustion control. The use of Ge- containing quartz single crystals can contribute to efficiency of combustion and solving one of the major environmental problems of the limitation of ejections of CO2 and CO to the atmosphere. This work was supported by RFBR (Grant 14-42-03654).
S04-P52 Dislocation multiplication during Czochralski growth of germanium: Numerical studies and experimental results
Miller Wolfram*1, Czupalla Matthias1, Abrosimov Nikolay1, Uta Juda1
1Leibniz Institute for Crystal Growth (IKZ), Max-Born-Str. 2, 12489 Berlin (Germany)
*email: [email protected]
The growth of germanium crystals with well-defined dislocation densities by means of Czochralski method is still a challenge. Especially, when growing germanium crystals with high purity by inductive heating the control of the thermal field inside the crystal during the growth process becomes difficult.
Wang et al. measured the dislocation density as a function of the vertical position in the crystal grown [1]. They compared the data with a computed ones based on the vertical temperature gradient. The radial distribution was not considered. We studied the thermal stress and the evolution of the dislocation density by means of dynamic global simulations employing the software tool CGsim. The Alexander-Haasen-Sumino model is used to compute the evolution of the dislocation density. However, there is some uncertainty in the value of some input parameters. Therefore, we have checked the influence of certain parameters on the dislocation density by varying the parameters and performing several runs for the same growth process. Another point of investigations was the thermal field in the vicinity of the melt/crystal interface. It is significantly influenced by the melt convection. On the other hand the thermal field is critical for the evolution of dislocation especially in this region because of its high temperature and hence of high velocity of dislocations. The numerical simulations have been performed for the furnace geometry and parameters of real growth experiments. The results of the calculations will discussed in comparison with the etch pit density measurements on wafers from these experiments.
References: [1] Guojian Wang,Yutong Guan, Hao Mei, Dongming Mei, Gang Yang, Jayesh Govani, J. Crystal Growth 393 (2014) 54
Acknowledgement
The help of Vasif Mamedov, Kirill Mazaev, and Andrey Smirnov in setting up the runs is gratefully acknowledged.
S04-P54 New technological approaches for electroless deposition of metal contacts on CdZnTe single crystals.
Manuele Bettelli*1, Giacomo Benassi2, Lucia Nasi1, Nicola Zambelli2, Davide Calestani1, Enos Gombia1, Leonardo Abbene3, Fabio Principato3, Andrea Zappettini1
1IMEM-CNR, Parco delle Scienze 37A, Parma (Italy) 2due2lab s.r.l., Parco delle Scienze 37A, Parma (Italy) 3Dept. of Physics and Chemistry, University of Palermo, Palermo (Italy) *[email protected]
Since many years our group growth Cd0.9Zn0.1Te with Boron Oxide Encapsulated Vertical Bridgman technique. The encapsulant prevents the contact between the growing crystal and the crucible quartz, thus improveing the quality of grown material. The monocrystalline material can be used to realize X-ray detectors, a major issue for their preparation being the deposition of the contacts. In particular, due to CdZnTe thermal instability above 150 degree Celsius, thermal annealing of contacts after deposition is not possible. Also for this reason, mechanical stability of contacts is usually poor. For the deposition of contacts we have adopted the electroless technique which is more rapid and economic then thermal evaporated or sputtering. Blocking contacts are usually adopted to realize high-resolution spectrometers, where minimization of dark current is required. On the other hand, one of the main exploitation fields for CdZnTe detectors is related to high flux applications. In this case, the use of ohmic contacts is preferred due to their capability to extract with high efficiency photo-generated carriers. Indium is traditionally employed to realize ohmic contacts on high resistivity CdZnTe crystals. However, indium electroless deposition is not easy, and evaporated Indium contacts usually show a poor mechanical stability. In this work, we describe a procedure to obtain gold and nickel contacts by electroless deposition. Deposited layer thickness up to 1 micron has been obtained. Current-voltage characterization has been carried out, paying attention to cut surface conduction by using a guard- ring. A ohmic behavior was found for nickel contacts and the contact resistivity seemed to be negligible with respect to material resistivity that is very important to have a high and homogenous electric field in the detector. Gold contacts showed blocking characteristic. In order to improve the mechanical stability of this contacts we have replaced the solvent in the electroless solution, a very good result was been obtained with the replacement of water with methanol. The obtained layers show good adhesion and can withstand standard tape test. EDS-TEM investigations demonstrate that in both the cases, the good adhesion is correlated with the good CdZnTe stoichiometry under the contact layer. CdZnTe planar detectors have been realized and spectroscopic characteristics have been obtained. Detectors with symmetric nickel contacts have been compared with detectors realized with nickel and gold contacts. In this work, the response of detectors with nickel contacts under high flux conditions is tested and reported.
S04-P55 Impurity distribution in characteristic of multicrystalline silicon growth mode
Nepomnyashchikh A.I., Presnjakov R.V. Vinogradov Institute of Geochemistry SB RAS, Irkutsk, 664033, Russia [email protected] At present multicrystalline silicon (mc-Si) is the basic material for solar cell production [1]. The basic problem restraining solar energy growth is the price for raw silicon. From this viewpoint, mostly promising is the refined metallurgical silicon with substance proportion from 99.9 at.% to 99.999 at.% in approaching to the regions of impurity solid solutions in silicon [2]. The key issue is to define the limit of impurity concentrations for refined silicon to obtain the material with set properties. The directional solidification of silicon proceeds along with segregation of metal impurities and formation of macro- and micro structure of the ingot. The features of heat and mass transfer, which set the parameters of growth process (e.g. velocity and gradients), affect the effective distribution coefficient of impurities. Experimental ingots mc-Si based on metallurgical silicon of set composition (Table 1) were grown under optimum conditions: 1) rotation of crucible- melt-crystal with minimum rate sufficient to equalize the thermal field; 2) movement of the crucible-melt-crystal in the zone with temperature gradient at sufficiently low rate to prevent concentration supercooling at the crystal interface [3]. The result of calculation of the effective distribution coefficients (keff) of these elements in the approximation of complete mixing of the melt (1) shows reduction of their values (Table 1) at increasing the impurity concentrations in the initial charge (C0): k 1 C C k (1 f ) eff (1), 0 eff where f is the fraction of crystallized silicon.
16 -3 Table 1. Main element contents in the initial charges to grow mc-Si (C0, × 10 cm ), effective 16 distribution coefficients of impurities corresponding to charges № 1-5, Cl - solubility limit (× 10 cm-3) [2]
Fe Ni V Ge Mn Co
C0 keff C0 keff C0 keff C0 keff C0 keff C0 keff №1 8450 0,002 387 0,006 544 0,00004 13 0,33 342 0,001 734 0,00001 №2 61 0,015 1,0 0,04 2,7 0,0015 0,008 0,33 0,39 - 1,8 0,001 №3 53 0,02 0,73 0,04 6,0 0,00015 0,02 0,33 1,0 0,017 4,6 0,0002 №4 18 0,04 0,21 0,04 2,0 0,003 0,01 0,33 0,29 0,035 1,6 0,0005 №5 2,6 - 0,03 - 0,3 0,01 0,002 - 0,04 - 0,2 - Cl 1,3 1,0 0,03 unlimited 1,5 4,0
We have identified the pattern of impurity distribution in the mc-Si ingots, indicating that the free convection in the melt takes place along with the significant impact of the diffusion substance transfer. With this in mind, we believe that for higher physical quality of mc-Si ingot the increased purity of raw silicon is the necessary condition, and the growth mode corresponding to this purity is a sufficient condition.
References: 1. Global market outlook for photovoltaics 2013-2017. (http://www.epia.org/) 2. Nakajima K., Usami N. Crystal growth of silicon for solar cells. – Springer Berlin Heidelberg. – 2009. – 259 p. 3. Nepomnyashchikh A.I., Presnyakov R.V., Eliseev I.A., Sokol'nikova Y.V. Specific features of multicrystalline silicon growth from high-purity commercial silicon // Technical Physics Letters, 37, 8 (2011) 739-742.
S04-P56 Growth of TbFe0.5Mn0.5O3 and Tb0.5Sr0.5MnO3 Single Crystals Using Optical Float-Zone Technique Hariharan Nhalil and Suja Elizabeth Department of Physics, Indian Institute of Science, Bangalore, India 560012
Single crystal growth of two materials, TbFe0.5Mn0.5O3 and Tb0.5Sr0.5MnO3, are discussed in detail. Both TbFe0.5Mn0.5O3 and Tb0.5Sr0.5MnO3 show interesting magnetic properties .TbFe0.5Mn0.5O3 single crystal is grown by optical float-zone method. High purity precursors Tb4O7, Fe2O3 and MnO2 are taken in stoichiometric ratio and mixed thoroughly using a mortar and pestle for several hours. After mixing properly, the material is sintered at 1200 °C for 24 hours. The sintered material is again mixed properly and calcined at 1250 °C for another 24 hours. The phase purity of the synthesized material is confirmed through room temperature powder XRD. Once the phase purity is confirmed, the powdered sample is made into ingots of sufficient length to be used as the feed rod in the optical float-zone furnace. A small piece of the same rod can be used as seed rod. Growth was performed at ambient pressure and in air atmosphere. The growth rate was 5mm/hr and the upper and lower shaft rotation rates being 30 and 35 rotations/min, respectively. Tb0.5Sr0.5MnO3 single crystal is also grown optical float-zone technique. High purity precursors Tb4O7, SrCO3 and MnO2 taken in stoichiometric ratio are mixed thoroughly using a mortar and pestle. After mixing properly, the material is sintered first at 1250 °C for 24 hours and again at 1300 °C for another 24 hours with intermediate grinding. Phase pure powdered sample is made in to feed and seed rods. The growth conditions were similar to TbFe0.5Mn0.5O3 except the growth rate. A growth rate of 3mm/hr is used for Tb0.5Sr0.5MnO3. Good quality single crystals are obtained in both case and the single crystalline nature is confirmed through Laue photograph.
S04-P57 3+ 3+ SrMoO4:Ho :Tm crystal as new active material for mid – IR laser Dunaeva E.E.*, Ivleva L.I., Doroshenko M.E., Zverev P.G., Nekhoroshikh A.V., Osiko V.V. A.M. Prokhorov General Physics Institute Russian Academy of Sciences, Vavilov str., 38, Moscow 119991, Russia *email: [email protected]
Solid state lasers, which operate in the spectral region around 2 µm, have great market potential for the use in LIDAR and gas sensing systems. Due to intense absorption by H2O these lasers can have many practical applications in a medical treatment. Crystalline materials doped with Tm3+ and 3+ 3 3 3+ Ho ions for developing 2 µm laser are based on the F4 → H6 optical transition of Tm (1.9 µm) 5 5 3+ 3+ and the I7 → I8 transition of Ho (2.1 µm). Tm ions can also be used as a sensitizer to transfer an absorbed pump energy to Ho3+ ions, so that high power commercial laser diodes at 790 nm can be used to pump Tm3+/Ho3+ co-doped systems. The tungstate and molybdate sheelite crystals doped with RE ions can combine good laser and nonlinear-optical properties and can be effectively used for developing of compact lasers with Raman self conversion. Recently it has been shown that SrMoO4 crystals exhibit high Raman gain coefficient [1]. The SrMoO4 crystal has good chemical stability and moisture resistance. Sheelite type structure of SrMoO4 crystal allows introducing RE ions in concentrations sufficient for laser generation. The strongest Raman mode (887 cm-1) corresponds to the breathing oscillation of four 3+ 3+ oxygen atoms. The development of SrMoO4 crystals doped with Tm /Ho ions could provide the oscillation at the main laser wavelength (1.9-2.1 µm) as well as at 2.22–2.6 µm and 2.77-3.38 µm the first and second Stokes components. In this work we have developed the growth technology of high optical quality SrMoO4 crystals doped with Ho3+/Tm3+ ions by Czochralski method from the melt in the air. We have obtained the 3+ 3+ 3+ concentration series of Ho :SrMoO4, Tm :SrMoO4 and SrMoO4 crystals co-doped with Tm (7.9·1019 cm-3) and Ho3+ (8.0·1019 cm-3). Typical dimensions of the crystals were 15x12x70mm. The SrMoO4 crystals were grown along the [100] crystallographic direction perpendicular to the optical C axis, that is characterized by the maximal Raman scattering cross-section. Due to similar ionic radius trivalent RE ions can replace Sr2+, but this requires special charge compensation. That is why Ho3+/Tm3+ ions were added into the melt in the niobates form. 3+ 3+ The spectroscopic investigations of Tm /Ho :SrMoO4 crystal have shown the absorption cross section of Tm3+ ions at 790 nm is strongly anisotropic. It reaches 1.1·10-20 cm2 for σ-polarized radiation, that is twice higher than that for π-polarized and higher than that in YAG and YLF 3+ 3+ crystals. The polarized fluorescence spectra of Tm /Ho :SrMoO4 crystal were measured under 3+ 3+ 795 nm excitation at T=300K and T=77K. Laser oscillations for Tm /Ho :SrMoO4 pumped by laser diode (790 nm) produced 1.6 mW output power at about 2 μm with an absorbed pump power of 90 mW with slope efficiency of 3%. The optimization of crystal composition and improvement of the cavity configuration could result in the increase of laser parameters. We believe, that 3+ 3+ Tm /Ho :SrMoO4 crystal can be a perspective material for developing mid-IR lasers with self- Raman conversion of radiation inside the active medium.
References: [1] Basiev T.T., Zverev P.G., Karasik A.Ya., Osiko V.V., Sobol A.A., Chunaev D.S., Journal of Experimental and Theoretical Physics, 99 (2004) 934–941.
S04-P59 Structural properties and spinodal decomposition of bulk ternary semiconductor compounds with oxygen in the anion sublattice
Natalia Podolska*1,2
1Saint-Petersburg Branch of Joint Supercomputer Centre, 26 Politehnicheskaia str., Saint-Petersburg (Russia) 2Ioffe Institute, 26 Politehnicheskaia str., Saint-Petersburg (Russia) *email: [email protected]
Semiconductor compounds with oxygen in the anion sublattice, such as CdO, ZnO, MgO, BeO and their ternary alloys (CdZnO, BeZnO, MgZnO), attract a very high attention in the last years due to wide perspectives for modern opto- (especial for green spectral region) and microelectronics [1- 4]. However, their specific properties and tendency to phase separation (both composition fluctuations and several crystal phase coexisting) produce many problems with reproducible growth of materials, based on these ternaries compounds and, consequently, with application to practice [5]. Additionally, there is a lack of experimental and theoretical works on structural (including interatomic distances) and thermodynamic properties of these semiconductor alloys. In the paper, we present the analysis of the structural (anion-cation, cation-cation and anion- anion distances) and thermodynamic properties (mixing energy, interaction energy and phase diagrams) of bulk wurtzite and zinc blende ZnxCd1-xO, ZnxBe1-xO and ZnxMg1-xO semiconductors as a function of composition "x". Good agreement with the experimental data was demonstrated. The reported study was partly supported by RFBR (Russian Foundation for Basic Research), research project for young researchers No.14-08-31581.
1400 Binodal Experimental data: 1200 Spinodal Brown J.J. and Hummel F.A., J.Electron.Soc. 111 (1964) 1052 Ishihara J. et al., Appl.Phys.Lett. 89 (2006) 091914 1000 Gruber T. et al., Appl.Phys.Lett. 83 (2003) 3290 800 Singh A. et al., ECS J.Solid State Sci.Technol. 2 (2013) Q136 Chien K.F. et al., J.Cryst.Growth 378 (2013) 208
600 Bertram F. et al., Appl.Phys.Lett. 88 (2006) 061915 400 Jiang J. et al., Journal of Alloys and Compounds 547 (2013) 59 Temperature (K) T = 978.8 K @ x=0.43 Shtepliuk I. et al., App.Surf.Science 276 (2013) 550 200 C Sartel C. et al., J.Vac.Sci.Technol.A 29 (2011) 03A114 Ohashi T. et al., Jap.J.App.Phy. 46 (2007) 2516 0 0.0 0.2 0.4 0.6 0.8 1.0 CdO mole fraction in CdZnO Figure 1. Phase diagrams of wurtzite CdZnO computed with the thermodynamic properties derived in this work. Solid line is binodal curve and dash-dotted line is spinodal curve. Circles are experimental data (right): grey circles denote unstable phase and black circles denote stable phase.
References: [1] Lee D.-H., Kim S., Lee S. Y., Thin Solid Films 519 (2011) 4361 [2] Lange M., Dietrich C. P., Brachwitz K., Stölzel M., Lorenz M., and Grundmann M., Phys.Status Solidi RRL 6 (2012) 31 [3] Jiang J., Zhu L. P., He H. P., Li Y., Guo Y. M., Cao L., Li Y. G., Wu K. W., Zhang L. Q., and Ye Z. Z., J. Appl. Phys. 112 (2012) 083513 [4] Özgür Ü., Alivov Y. I., Liu C., Teke A., Reshchikov M. A., Doan S., Avrutin V., Cho S.-J., and Morkoç H., J. Appl. Phys. 98 (2005) 041301 [5] Venkatachalapathy V., Galeckas A., Trunk M., Zhang T., Azarov A., and Kuznetsov A. Yu., Phys. Rev. B 83 (2011) 125315
S04-P60 Li2MoO4 crystal growth from solution activated by low-frequency vibrations
Andrey Sadovskiy*, Olga Barinova, Svetlana Kirsanova, Stanislav Belov, Ivan Ermochenkov, Marina Zykova, Andrew Khomyakov, Elena Mozhevitina, Igor Avetissov
D.Mendeleyev University of Chemical Technology of Russia, Miusskaya pl.9, Moscow (Russia) *email: [email protected]
Molybdenum based crystals are known as effective materials for cryogenic phonon-scintillating detectors and they are widely used for 100Mo 2β-decay investigations and dark matter search [1]. The most perspective detectors so called «active» detectors allow realizing the generation of rare nuclear event and its registration in the same crystal. The crystal materials for these detectors have basically a scheelite-type structure (CaMoO4, CdMoO4), and a high light yield at low temperature. Unfortunately, all of them have long-lived radioactive isotopes (48Са,116Cd) entangles neutrinoless 2β-decay searches. In [2] we have analyzed the properties of CZ-grown 50 mm diameter transparent Li2MoO4 crystals and showed the difference in Raman spectra for ||с oriented and c oriented crystals and the 2- absence of MoO4 complex distortions. In this research we try to get ultra-low-background radioactive detector material based on Li2MoO4 crystal grown from water solution. One of the main problems of solution growth technique is a small growth rate. The Li2MoO4 solution is very complex and has large size associates which decrease the solution viscosity and reduce the growth rate. In [3] it was demonstrated that application of axial vibration control (AVC) technique could change a liquid structure by destroying associates. We have grown Li2MoO4 crystals from AVC activated water solution and investigated their spectral and physical properties in comparison with CZ-grown and normally water grown crystals as well as a crystal purity. It was found out that AVC-crystals were grown with the rate in 2 times higher comparing to normally grown crystals. The purity of AVC grown crystals analyzed ICP-MS towards U and Th was <0.01 ppb and <0.05 ppb, correspondingly. The AVC-grown crystals had structure (rocking curves) and spectral (transmission, Raman) characteristics close or higher than the CZ-grown crystals. The research was financially supported by the Ministry of Science and Education of Russia grant N 14.577.21.0146.
References: [1] V.B.Mikhailik, H.Kraus. J.Phys.D: Appl.Phys. 39 (2006) 1181-1191 [2] O.Barinova, S.Kirsanova, A. Sadovskiy,I. Avetissov J.Cryst.Growth 401c (2014) 853-856 [3] A.Sadovskiy, E. Sukhanova, S. Belov, V. Kostikov, M.Zykova, V. Artyshenko, E. Zharikov, I. Avetissov J.Cryst.Growth 417 (2015) 16-24
S04-P63 Investigation of some key working parameters in a Kyropoulos process for silicon using numerical modeling.
Nouri Ahmed *1, 2, Delannoy Yves 1, Lhomond Leslie 1, Chichignoud Guy 1,3, Helifa Bachir 2, Lefkaier Ibn Khaldoun 2, Zaidat Kader 1
1 Univ. Grenoble Alpes, SIMAP, F-38000 Grenoble, France 2 LPM laboratory, Laghouat University, 3000Laghouat, Algeria 3 CNRS, SIMAP, F-38000 Grenoble, France *email: [email protected]
The Kyropoulos crystal growth technique can produce high quality bulk crystals for applications requiring low dislocation density thanks to lower thermal gradients in the melt. Our work investigates the growth of square shaped silicon ingots for photovoltaic applications using Kyropoulos process. We present our numerical simulation of silicon ingots solidification in a modified DSS furnace with three heating zones operating as a Kyropoulos machine. Due to the square geometry of the crucible, 3D modeling was carried out to calculate the temperature distribution as well as fluid dynamics and solidification. Experimental and numerical investigations progressed in parallel to study the growth conditions. The obtained experimental results are favorably in agreement with the simulation model results. We compare, in this work, different Kyropoulos configurations and different operating parameters of heating distribution to highlight the effects of these modifications on the final solidified crystal.
S04-P64 Effectivity of chemical vapor transport for ZnO single crystal growth based on HCl vapors
Colibaba Gleb* 1,2, Shtepliuk Ivan3, Goncearenco Evgenii1, Inculet Ion1
1Moldova State University, A. Mateevici 60, MD-2009, Chisinau, Moldova 2Kazan Federal University, Kremlevskaya 18, 420008, Kazan, RF 3 Linkoping University, 581 83, Linkoping, Sweden *email: [email protected]
The thermodynamic analysis for use of HCl as a chemical vapor transport agent (TA) for ZnO single crystals growth in the closed growth chambers is carried out in comparison with Cl2, H2 and CO. High density of products for HCl+ZnO interaction, that is favorably for high quality of grown crystals, as well as low temperature dependence of the product densities limiting the rate of ZnO mass transport are predicted. The thermodynamic analysis for use of HCl+H2 and HCl+carbon mixtures is carried out and the possibility of increase in the growth rate is shown (Fig. 1(a)).
The influence of the growth temperature in the range of 775-1050 °С, density of HCl/HCl+H2/HCl+C TA and undercooling were investigated experimentally on the rate of ZnO mass transport. It is shown that the use of hydrogen and C/CO as a TA for ZnO is limited by low structural perfection of the obtained crystals and their destruction during a post-growth cooling because of a strong mechanical contact between grown materials and walls of quartz growth chambers. The use of HCl with a high density up to several atm is favorable for the growth of voids free crystals; however, it is limited by the low rate of mass transport. The use of HCl+H2 gas mixture or HCl+C as a TA is useful for 950-1050 °С growth temperature range and also has following advantages: (i) the increase of growth rate in 4-6 times up to 1 mm per day (Fig. 1(b)); (ii) reduction of the growth nucleus density down to 1-3 cm-2; (iii) seeded growth of single crystals (having diameter up to 2 cm) densely filling of the growth chamber volume; (iv) absence of the essential attachment effect and destruction of crystals during a post-growth cooling and not typically low dislocation density down to 0-4 mm-2. The use of HCl+C TA is more preferred and stable as it allow to avoid necessity of continuous supply of hydrogen to the quartz growth chamber.
Figure 1. Temperature dependence of the pressure of products for HCl+H2+ZnO interaction (a) (loaded pressure of HCl and H2 = 1 atm). Influence of the growth temperature on ZnO mass transport rate (b). This work was supported by the Moldavian National grant No.14.819.02.14A, and partially by the Russian Government (agreement No.02.A03.21.0002) to support the Program of Competitive Growth of Kazan Federal University among World’s Leading Academic Centers.
S04-P66 Temperature dependent optical absorption of strontium titanate
Kok, Dirk Johannes 1*, Irmscher, Klaus1, Naumann, Martin1, Guguschev, Christo 1, Galazka, Zbigniew1 and Uecker, Reinhard 1
1Leibniz Institute for Crystal Growth, Max-Born-Str. 2, Berlin (Germany) *email: [email protected]
SrTiO3 is a prevalent epitaxy substrate for numerous oxide films and the only substrate crystal for all known oxide based two dimensional free electron gas systems [1]. At present, the performance of such epitaxial structures suffers from low quality of the available substrates which are commercially grown by the flame fusion (Verneuil) method [2,3]. The most preferred growth method for high-quality bulk oxide crystals is the Czochralski method. But in case of SrTiO3, growth instabilities such as foot formation and spiraling make it impractical. These instabilities indicate insufficient radiative heat transport through the crystal at high temperatures. To investigate the temperature dependence of the radiative heat transport, the optical absorption edge and the near infrared absorption of SrTiO3 were measured at temperatures from 4 K to 1703 K. The absorption edge decreases from 3.27 eV at 4 K to 1.9 eV at 1703 K and is extrapolated to approximately 1.3 eV at the melting point (2350 K). Because of free carrier absorption the transmission in the near IR decreases rapidly above 1400 K. At 1673 K it is only about 50% of the room temperature value. The free carriers are mainly generated by thermal excitation of electrons over the band gap. The measured red shift of the optical absorption edge and the rising free carrier absorption strongly narrow the spectral range of transmission and impede radiative heat transport. To minimize problems associated with radiative heat transport through the growing crystal, single crystal growth experiments were performed using the top-seeded solution growth method (i.e. TiO2-rich melt) at temperatures below 1540°C [4]. High quality, cylindrical SrTiO3 crystals were obtained with this method, with none of the instabilities characteristic of high temperature growth evident.
Figure 1. Measured and extrapolated band gap of SrTiO3.
References: [1] A. Ohtomo, D. A. Muller, J. L. Grazul, and H. Y. Hwang, Nature, 419 (2002) 378. [2] J. Bednorz and H. Scheel, J. Cryst. Growth 41 (1977) 5. [3] S. Thiel, C. W. Schneider, L. Fitting Kourkoutis, D. A. Muller, N. Reyren, A. D. Caviglia, S. Gariglio, J.- M. Triscone, and J. Mannhart, Phys. Rev. Lett. 102 (2009) 046809. [4] Guguschev, C.; Klimm, D.; Langhans, F.; Galazka, Z.; Kok, D.; Juda, U. & Uecker, R, Cryst.Eng.Com 16 (2014) 1735.
SESSION 5 Advance in Crystal Growth Technology
Numerical modeling and experimental validation of electromagnetical stirring in unidirectional solidification of multicrystalline silicon Negrila Radu Andrei1, Popescu Alexandra1 ,Vizman Daniel*1 1Faculty of Physics, West University of Timisoara, Bd. V. Parvan 4, 300223, Timisoara, Romania *email: [email protected]
The quality of multicrystalline silicon grown by directional solidification (DS) method is strongly related with the control of the impurities distribution in the mould. It is well known that melt convection plays an important role in the impurities distribution. Therefore, a control of melt convection will improve the quality and yield of the solidification process by influencing the interface shape and dopant and impurities distribution in a beneficial way. For a better control of the flow in the whole melt volume, we propose a stirring method (figure 1) based on the idea of a combination between a static magnetic field B and an electrical current I, giving rise to an electromagnetic force which has a significant melt stirring effect, even for small values of I and B[1,2].
Figure 1. Schematic representation of the electromagnetic stirring method In order to understand the basic features of the melt flow in a DS-like configuration under electromagnetic stirring, an isothermal model experiment in a rectangular crucible filled with a room temperature GaInSn melt and a corresponding time-dependent numerical model, were developed. Experimental velocity profiles measured by Ultrasound Doppler Velocimetry confirmed the flow structure obtained in the numerical simulations. A parametrical study for a range of I and B values was performed, in the case of a symmetrical electrode positioning along the diagonal of the free melt surface. The resulting flow structure was analyzed and described in terms of a vortex or a poloidal recirculation domination and a transition between the two. A characteristic parameter was defined to quantify the different flow structures. Through the use of scaling analysis, two dimensionless numbers corresponding to the two Lorentz force components were identified and a good correlation between their values, flow structure and maximal velocity was observed. This correlation makes possible the prediction of the flow structure for any set of the system parameters I and B and a characteristic crucible length. The same conclusions would hold for a silicon melt if the dimensionless numbers are conserved by choosing different I and B in respect with the different material constants. The main contribution of this idea is to provide some additional growth parameters (like intensity of electrical current and position of the electrodes) easy to be adjusted in order to control the melt flow and interface shape.
[1] D. Vizman, C. Tanasie, J. Cryst. Growth 372 (2013) 1-8 [2] R.A. Negrila, A. Popescu, D. Vizman, Eur. J. of Mechanics-B/Fluids 52 (2015) 147-159
Crystal Growth of Cd1-xZnxTe by the Traveling Heater Method in Microgravity on Board of Foton-M4 Spacecraft E. B. Borisenko1, N. N. Kolesnikov1, A. S. Senchenkov2, M. Fiederle3
1 Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Russia e-mail: [email protected] 2 Research and Development Institute for Launch Complexes, Moscow, Russia 3 Materials Science Center, University of Freiburg, Freiburg, Germany
The task of crystal growth of CdTe and Cd1-xZnxTe (CZT) bulk specimens is stipulated by needs in high-resolution ionizing-radiation detectors. These crystals, especially the ternary solution doped with 6-10 at.% Zn, are very efficient for performance even at room temperature, without cooling. These materials are attractive due to their high atomic number, high specific resistivity associated with low leakage current, wide band gap, which provide high resolution and long-term stability of X-ray and gamma-ray detectors at room temperature. The purpose is to grow perfect bulk crystals, with low density of structural defects and homogeneous stoichiometric content. Using of the traveling heater method (THM) provides the solution-in-melt growth, which results in purification from foreign impurities and more uniform composition than in the case of the traditional Bridgman (HPVB) or High Pressure Vertical Zone Melting (HPVZM) growth. But more than this, since a crystal is grown from solution in melt via Te liquid zone, the growing temperature was lowered considerably as compared to the melt growth, which allowed the experiment on board of the Foton-M4 spacecraft launched for two-month trip in space. Why we consider crystal growth in microgravity advantageous as compared to the terrestrial THM growth? Structural defects, structural and chemical heterogeneities, pores, grain boundaries appear due to gravitational convection. In space, in microgravity, diffusion and convection are approached to stationary processes far closer than at presence of the gravitational field. The crystals grown on board of Foton-M4 spacecraft and under terrestrial conditions via THM are considered in this study. The parameters of the crystal growth obtained from the diffusion and the convection mixing models conform to optimal experimental parameters under microgravity conditions [1]. A CZT feed and single crystalline CdTe seed were loaded in a quartz ampoule, the traveling Te-rich liquid zone was installed. The solvent zone width was 26 mm, the estimated temperature on the interface was 780 ºC. The pulling rate was 0.3 mm/h, by ~10 times lower than in the case of HPVB or HPVZM. The grown crystals were 32 mm in diameter and 42-43 mm in length. High- resistant crystals were obtained upon growth from the Te-rich solution. According to the X-ray diffraction data, the crystal grown in microgravity is a single crystal with a cubic phase with sphalerite lattice, a = 6.458Å, which coincides precisely with the calculated unit cell parameter for this composition. The measured IR transmission reaches ~70%. The measured Vickers microhardness HV under load 50 g is 640 MPa for the terrestrial crystal and 540 MPa for the crystal grown in Space. Spread of the data for is about 6% for the former crystal, and less than 2% for the latter crystal. We can conclude that the THM growth of CZT in microgravity results in production of the crystals with homogeneous composition and in improvement of structural perfection as compared to the crystals grown under terrestrial conditions. Consequently, THM growth in microgravity has a positive effect on many properties of these crystals.
References 1. A.S. Senchenkov, M. Fiederle, and N.N. Kolesnikov, IAC-14-A2.4.7.
Modified Bridgman technique for growing Sb-based binary compounds Pillaca Mirtha*1, Miller Wolfram2, Cocivera Viviane1, Maletin Tamara1, Gille Peter1 1Department of Earth and Environmental Sciences, Crystallography Section, Ludwig‐Maximilians‐Universität München, Theresienstrase 41, 80333 München (Germany) 2Leibniz Institute for Crystal Growth (IKZ), Max‐Born‐Str. 2, 12489 Berlin (Germany) *email: [email protected]
Many binary intermetallic compounds cannot be crystallized from congruent melts but have to be grown below their specific peritectic temperature. E.g. FeSb2 and CoSb3 which are considered interesting materials for thermoelectric applications can only be grown from Sb-rich solutions containing more than 90 at. % Sb. Moreover, due to the relatively high Sb vapor pressure crystal growth has to be carried out in closed ampoules, e.g. using the Bridgman method from a high- temperature solution. In vertical Bridgman growth buoyancy-driven convection is very weak because of the vertically stable thermal conditions. Rotation of the ampoule increases the convection but numerical simulations show that this not is enough to evoke a sufficient mixing in the vicinity of the interface. Strong mixing is mandatory in order to remove the rejected Sb excess from the phase boundary of the growing crystal. Without sufficient mixing second-phase inclusions have been found in the crystal grown.
Crystals of both FeSb2 and CoSb3 grown by the vertical Bridgman method exhibit a high density of Sb inclusions, even with extremely low growth rates of less than 1 mm/d. Three-dimensional calculations of melt convection by employing the commercial software ANSYS-cfx show that a much better mixing is achieved by tilting the Bridgman furnace. Computations have been performed for a tilting angle of 75° with respect to the axis of gravity. Now, there is a temperature variation in horizontal direction, which causes a Rayleigh-Benard instability and hence a convection. Additional rotation of the inclined ampoule adds a forced convection resulting in a time-dependent behaviour of the melt flow. This provides an efficient transport all along the interface. Experiments using this Inclined Rotary Bridgman technique resulted in single-phase ingots of FeSb2 and CoSb3.
Experimental evidence that a high electric field acts as an efficient external parameter during crystalline growth of bulk oxide
R. Haumont1,2, P. Hicher1, R. Saint-Martin1, X. Mininger3, P. Berthet1
1 Equipe Synthèse, Propriétés et Modélisation des Matériaux, ICMMO, CNRS-UMR8182, Université Paris Sud, 15 rue Georges Clémenceau, 91405 Orsay Cedex, France 2 Laboratoire Structures, Propriétés et Modélisation des Solides, CNRS-UMR8580, Ecole Centrale Paris, Grande Voie des Vignes, 92295, Chatenay-Malabry Cedex, France 3 Laboratoire de Génie Electrique de Paris, SUPELEC, CNRS-UMR 8507; Université Paris Sud, 11 rue Joliot Curie, 91192 Gif-sur-Yvette
The aim of the talk is to present a new way to design bulk functional oxide: a new crystal growth device, in which a high static external electric voltage (up to 14 kV) was added to a floating zone method. Our first experiments show that the application of such an electric field acts like an external force, introducing a pressure effect which is in direct competition with temperature in the solid/liquid thermodynamic equilibrium. High electric fields could therefore be an additional parameter in crystal growth, opening original routes to the synthesis of new materials.
ECCG5-2015 Bologna Italy High-pressure and ambient gas effect on the optical floating zone crystal growth of novel oxide and intermetallic compounds
Paul Sass*, Robert Schöndube
ScIDre GmbH –Scientific Instruments Dresden, Großenhainer Str, 101, 01127 Dresden (Germany) *email: [email protected]
Floating zone (FZ) techniques enable the growth of surpassing quality single crystals. The feasibility to control and to enhance parameters like growth atmosphere and temperature in a wide range during the FZ growth with optical radiation heating leads to the creation of heretofore unknown compounds with striking properties. Various novel oxide and intermetallic phases with complex behavior have been successfully grown with optical FZ methods. We illuminate the potentials of high pressures and different gases for the FZ crystal growth and place particular emphasis on strongly correlated materials. During the FZ growth process of intermetallic compounds, high-purity protective gases like argon are used to avoid reactions with the melt. Due to their low partial pressure in these atmospheres, volatile elements and constituents with low melting and boiling points can evaporate from the molten zone. Applying low gas pressures down to vacuum conditions can stimulate the volatilization of impurity elements and lead to melt purification during the growth process. However, the selective evaporation is normally an undesired phenomenon because it shifts the stoichiometry of the melt and the growing crystal. High-pressure atmospheres of inert gases substantially restrain the evaporation from the molten zone and enable the creation of intermetallic phases which would remain elusive under low ambient pressures. Elevated gas pressures are also used in the floating zone growth of oxides to reduce evaporation losses and to maintain the stoichiometry of the molten zone. Furthermore, specifically the O2 partial pressure interacts in subtle way with the thermodynamic stability of cationic valence states at melting temperature. Depending on the intended process, this interaction might lead to the necessity of elevated pressures of inert gases, precise gas mixtures or generally a well-controlled O2 partial pressure during the growth process. On the other hand, elevated oxygen pressure has been proved to affect directly the thermodynamic equilibrium and the solidification behavior of oxidic compounds. For some materials, which melt incongruently in air or at low and normal pressure, congruent melting can be achieved with significantly increased O2 pressure. The oxygen diffusion between the melting zone, the crystal and the atmosphere can be controlled by applying a wide range of ambient O2 pressures during the growth process. Thus, the O2 partial pressure affects not only the solidification mode of oxides but also the composition, homogeneity and physical properties of the crystals themselves. In recent times, floating zone crystal growth with ambient gas pressures > 15 MPa becomes feasible. We introduce and discuss several novel applications of high pressure and their advantages for the growth process.
Growth of Shaped Oxide Eutectics by the EFG Technique Stryukov Dmitry*, Shikunova Irina, Kurlov Vladimir
Institute of Solid State Physics Russian Academy of Sciences, 2 Academician Ossipyan str., 142432 Chernogolovka, Moscow District, Russia *email: [email protected]
Directionally solidified eutectic ceramic oxides have a high hardness, melting point, very good thermal conductivity, tensile strength and thermal shock resistance. They are very interesting and attractive as structural materials for high-technology applications (aeronautics, aerospace, power generator technologies etc.), first of all, because of their inherent high strength, high oxidation and creep resistance at temperatures up to 1600ºC. The optimization of standard solidification technologies and development of new techniques are actively pursued in order to increase the dimensions of ceramics, improve the quality, homogeneity and stability of microstructure, reduce the cost of material, and obtain complex shapes during the solidification process. Oxide eutectics of any predetermined cross-section, constant along the crystal length (rods of various cross-sections, ribbons, tubes, fibers, etc.), have been grown by the EFG technique, Fig. 1. The method has been used to obtain a variety of the shaped binary eutectics, such as Al2O3- Y3Al5O12, Al2O3-Er3Al5O12, Al2O3-GdAlO3, and one ternary eutectic system Al2O3-ZrO2(Y2O3). Mechanical properties and microstructure of various oxide eutectics (Fig. 2) depending on growth rates were investigated. The garnet eutectics have “chinese script” structure. The specific dimensions of phases corresponded to Hunt-Jackson law at growth rates from 30 to 300 mm per hour. Some perovskite eutectics contain rod-like structure with single crystalline phases, which makes them attractive for photonic applications.
Figure 1. Shaped Al2O3-Er3Al5O12 eutectics grown by the EFG method
Figure 2. Microstructure of Al2O3-Y3Al5O12 (at the left), Al2O3-ZrO2(Y2O3) (at the middle) and Al2O3- GdAlO3 (at the right) eutectics grown by the EFG method
High-pressure crystallization of organic compounds in a diamond-anvil cell
Michał Andrzejewski1, Andrzej Katrusiak1
1Department of Materials Chemistry, Adam Mickiewicz University, Umultowska 89b,61-614 Poznan (Poland) *email: [email protected]
Diamond-anvil cell (DAC) is a simple apparatus which provide possibility to study materials under extreme pressure conditions [1,2]. Thus, utilizing Xrays diffractometry, it is easy to observe structural changes in a single crystal. This is well known that pressure may induce phase transitions, resulting in new crystal forms. Hence, it is a perfect method for exploring phase diagrams and polymorphism. Moreover, there are many examples of significant geometric, conformational and packing changes in a crystal which are associated with physical properties like negative compressibility, spin cross-over, amorphisation, molecular conduction [3]. High-pressure crystallization in a DAC (both isochoric and isothermal) is a unique method for controlling a single crystal growth (Figure 1). It is crucial to select a proper solvent which is also pressure transmitting medium. Organic compounds, due to their low melting temperature, are effortless in crystallization and a sample may be prepared usually within few hours.
Figure 1. An isochoric growth of a single crystal in a diamond-anvil cell and the cross section of a DAC with two diamonds squeezing a sample in a metal gasket.
References: [1] Katrusiak A., Acta Cryst., A64 (2008) 135-148. [2] Merrill L., Bassett W. A., Rev. Sci. Instrum. 45, (1974), 290-294. [3] Tidey P.J., Wong H.L.S., Schroder M., Blake A.J., Coord. Chem. Rev. 277-278, (2014), 187-207.
Direct measurement of the crystallization pressure at the pore scale
Julie Desarnaud1*, Daniel Bonn1, Noushine Shahidzadeh1
University of Amsterdam , Institute of Physics, Science Park 904, 1098 XH Amsterdam (The Nederlands) *email: [email protected]
The precipitation of salt minerals in confinement (e.g. pores in porous media) is known to severely damage buildings, to be responsible for the weathering of rocks and to reduce the permeability in oil reservoirs. In all of these cases, crystal growth occurs within the pore spaces of the material, inducing mechanical stresses on the scale of the individual grains or pores. A condition for damage to occur is that the crystal continues to grow even in confinement, and that the resulting stress damages the rock or stone. Arguments explaining that growing crystals can exert a pressure have been given for more than 150 years; From the first experiments of Lavalle in 1853 and Becker et al 1905, it has been concluded that a crystal can grow under external pressure1. The authors argued that a crystal surface under pressure could grow and overcome the external forces resisting growth provided the surface is in contact with supersaturated solution1. Later, Correns2 gave the first equation for the crystallization pressure and its relation with the supersaturation , which was corrected subsequently by other authors 3. However, different experimental results for different salts published in the literature 4,5 open the debate on the mechanism involved in the development of such a pressure especially as according to both Riecke’s principle and crystal growth theories, a mechanically constrained crystal because of its higher solubility should dissolve4 rather than exert a pressure. Consequently, for understanding the deterioration mechanism of crystal growth, a direct measurement of the crystallization pressure exerted by crystals growing in a confined environment is needed. We present a novel method that we have developed in order to directly measure the crystallization pressure exerted by a growing microcrystal in a confined geometry under controlled environmental conditions6. This new method allows us to follow simultaneously the nucleation and spontaneous growth of the crystal from the salt solution and to measure the subsequent pressure developed at the pore scale. The important role played by the wetting properties and the nature of the salt on the development of a pressure during the growth will be discussed References: [1]. S.Taber. The growth of crystals under external pressure, American Journal of Science V,41, (1916) [2]. 532-556. [3]. CW.Correns , Growth and dissolution of crystals under linear pressure, Discuss Faraday Soc.5, (1949) 267-271. [4]. R.J.Flatt, M.Steiger, G.W.Scherer, A commented translation of the paper by C.W.Correns and W.Steiborn on crystallization pressure, Envion. Geol. 52 (2007) 187-203. [5]. J.Desarnaud et al. , Growth and Dissolution of Crystal under Load: New Experimental Results on KCl , Crystal growth and design 13 (20130, 1067-1074, [6]. K.Sekine, A.Okamoto, K.Hayashi, In situ observation of the crystallization pressure induced by halite crystal growth in a microfluidic channel. American Mineralogist, 96, (2011) 112-119. [7]. J.Desarnaud, D.Bonn, N.Shahidzadeh, Direct measurement of the crystallization pressure at the pore scale, submitted
POSTER
S05-P01 Isostructural phase transition of 2,4,5-triiodoimidazole at high pressure Kacper Rajewski, Michał Andrzejewski, Andrzej Katrusiak.
Adam Mickiewicz University, Department of Materials Chemistry, Unultowska 89b 61-614 Poznań email: [email protected]
Switchable polarization of NH•••N hydrogen bonds remains in a great interest of crystallographers due to their ferroelectric properties. This effect has been recently reported for dabco salts and halobenzimidazoles [2]. Halogen interactions are kind of electrostatic interaction that can be as strong as hydrogen bonds and may force different molecules arrangement in space. What is more X•••X interactions can significantly shorten NH•••N bond length and allow proton transfer along hydrogen bond chains. We have recently reported structural studies of several imidazole haloderivatives [2]. 2,4,5-Triiodoimidazole (TIIm) at ambient conditions crystallize in P21/a space group with Z’=3. High pressure experiments led to a new 2,4,5-triiodoimidazole ring arrangement. Phase transition is isostructural and nondestructive.
Figure 1. (a) structure of TIIm at ambient conditions, (b) high‐pressure structure of new phase
References: [1] S. Horiuchi, F. Kagawa, K. Hatahara, K. Kobayashi, R. Kumai, Y.i Murakami Y. Tokura, Above-room-temperature ferroelectricity and antiferroelectricity in benzimidazoles, 2012, Nature Communications 3, Article number: 1308. [2] M. Andrzejewski, J. Marciniak, K. Rajewski, A. Katrusiak, Halogen and hydrogen bonds architectures in switchable chains of di- and trihaloimidazoles, 2015, Cryst. Growth Des. 15 1658-1665
S05-P02 + - - + pH specific single crystal growth of N-H …Cl influenced [ZnCl4] [R] hybrid materials of 3D to 2D lattice dimensionality by organic variant: Microscopy, optical Eg and PL properties. Dinesh Jasrotia1*, Sanjay K. Verma1, B. Sridhar2 and Ajit Kumar1
1Department of physics ,Govt. Gandhi Memorial Science College, Jammu-180016, Jammu and Kashmir India. 2Laboratory of X-Ray Crystallography, CSIR-Indian Institute of Chemical Technology Hyderabad, India. *email: [email protected]
Single crystal growth process and detailed physicochemical characterization such as XRD, Structure stability with non-covalent interactions, UV-Vis spectroscopy, FESEM image analysis, lattice dimensionality (3D-2D) and luminescence property correlations were used in interweaving the design of two inorganic-organic hybrid materials. Single tube diffusion method in silica gel medium has been used to establish the conducive conditions for single crystal growth of bis(2- methylpyridine)tetrachlorozincate [MPCZ]. Gel medium with different pH were tried but diffraction quality single crystals were obtained at 5 pH of sodium metasilicate gel, ZnCl2 as lower reactant of 0.5M, 2-methylpyridine as upper reactant with conc. of 1M and Gel column length of 12 cm. Single crystal growth of bis(2-amino-5-chloropyridine)tetrachlorozincate [ACPCZ] has been performed by solution growth (SG) and slow cooling (SC) process by adding zinc chloride [0.092g], 2-Amino-5-chloropyridine [0.102g] and 5ml of HCl. Complete dissolution is achieved in 10 hours at 100oc and the solution was cooled slowly in 48 hours which results good quality single crystals of hybrid material. Single crystal X-ray diffraction structure analysis has been performed for MPCZ and ACPCZ hybrid compounds which depict that the N-H+…Cl- hydrogen interactions held the inorganic and organic moieties together into hybrid composite. In MPCZ hybrid material, organic moiety form 3D spreader shape pattern [6.89 x 4.44 x 4.15Å] and the inorganic moiety link the train of spreaders along ac-plane whereas the change in organic in ACPCZ moiety has 2D shear grade pattern of inorganic-organic components along b-axis with steepness grade of 1.29 and angle of inclination of 49.5o. FESEM image of MPCZ depicts that the surface of the hybrid materials filled with spherical granules and the shape descriptor indicates the average granular size of 28nm and circularity of 0.964 whereas the image of ACPCZ shows variation in spatial parameters of average granular size of 60nm due to alteration of organic derivative from 2-methylpyridine to 2-amino-5-chloropyridine. The change in optical energy direct band gap value from 3.01eV for MPCZ to 3.42eV for ACPCZ indicates the role of organic compounds in optical properties of hybrid materials. The photoluminescence emission spectra is observed in the wavelength range of 384 to 590 nm with maximum peak intensity of 9.66 a.u. at 438 nm for MPCZ and 388 to 600 nm with maximum peak intensity of 9.91 a.u. at 442 nm for ACPCZ, indicate the emission spectra lies in visible range.
Fig.: Photoluminescence and physicochemical depiction of [ZnCl4]- [R]+ hybrids.
S05-P04 Heptadecane and Gallium Crystallization in Hydrodynamic Czochralski Model
Berdnikov Vladimir1, Prostomolotov Anatoly2*, Verezub Nataliya2, Vinokurov Victor1
1Institute of Thermophysics of Siberian Branch of Russian Academy of Sciences, Lavrentev ave. 1, Novosibirsk (Russia) 2Institute for Problems in Mechanics of Russian Academy of Sciences, Vernadskogo ave. 101(1), Moscow (Russia) *email: [email protected]
This work presents a development of our investigations made without crystallization process by using ethanol as the modeling medium [1]. Processes of convective heat transfer and crystallization were studied on basis of the simplified, but the common calculation-experimental Czochralski model by using the two materials having the room melting temperatures: 1 – heptadecane having a low thermal conductivity and 2 – gallium having a high its value. The transparency of heptadecane melt (with melting temperature at 295 K) allowed to visualize a melt stream and geometry of its crystallized mass in this experiment and to provide the data for a verification of the corresponding calculation model. The results of such verification were successful and they are shown in Fig. 1. Numerical modeling has allowed to study parametrically the heat fluxes on the cooled disc and a convexity of melt-crystal interface for both these substances in the modes of thermal and mixed convection (i.e. with an additional crystal rotation). The means of effective influence on melt- crystal interface based on the controlled change of crystal rotation rate during growth process [2] have been analyzed.
1 1 2 2
b
а
1 1 2 2
d c
Figure 1. Crystallization of heptadecane (1 – cooled disk, 2 – crystalline portion) during thermal convection (a,b) and at joint action of thermal convection and crystal rotation (c,d): a,c – streamlines (left of the axis) and temperature contours [K] (right of the axis); b,d – photo of crystalline portion of this material (dark area).
References: [1] Berdnikov V.S., Prostomolotov A.I., Verezub N.A., J. of Crystal Growth, 401 (2014) 106. [2] Verezub N.A., Nutsubidze M.N., Prostomolotov A.I., Fluid Dynamics, 30-4 (1995) 510.
S05-P06 Growth of large size YAG:Ce crystals with homogenous distribution of Ce3+ ions by HDC method for WLED application
Nizhankovskyi S.V.*1, Tan’ko A.V.1, Savin Yu.N. 1
1Institute for Single Crystals, State Scientific Institution “Institute for Single Crystals” of National Academy of Sciences of Ukraine, Lenin 60, Ave, 61001, Kharkiv, Ukraine *email: [email protected]
Due to the high temperature stability and efficiency of luminescence, high thermal conductivity YAG:Ce garnet crystals have promising application in high-power white light-emitting diodes (WLED) as luminescent converters of blue light emitted by InGaN LED (460 nm). One of the most effective methods for growing of large size garnet crystals is horizontal directional crystallisation method (HDC). This method is a variation of zone melting, and allows to use its advantages associated with the ability to control the composition of the ingot along its length [1]. The aim of this work was to specify the conditions for growing large-size YAG:Ce crystals with a uniform distribution of the activator (Се3+ ions) along of crystal length and optimize their light- converting characteristics. It is found that the distribution of the activator in the crystal greatly depends on its distribution in the starting material, the ratio of the melt zone to the length of the crystal, the convective conditions in the melt, and other factors. It is shown that the use of a gradient doping of starting material allows one to obtain YAG:Ce crystals (up to 100×150×25 mm3) with high homogeneity of Ce3+ ion distribution (ΔC <8-10%), high optical and luminescent properties (Fig. 1a, b). Investigation of light-converting characteristics of YAG:Ce crystalline plates made of grown crystals showed that the color emission characteristics depends not only on the concentration of ions of Ce3+, but also on surface morphology of the plates (Fig. 1c). As a result of parameters optimization we showed that the of the possibility of creating WLED with YAG:Ce crystalline plates with correlated color temperature of ТCC ≈ 5000-6000 K and color rendering index CRI ≈60- 70.
Figure 1. (a)-YAG:Ce crystal grown by HDC method ; (b) -YAG:Ce crystalline plates; (c) – Color characteristics of LED with YAG:Ce crystalline plate. References: [1] S.V. Nizhankovskiy, E.V. Krivonosov, V.V. Baranov Inorganic materials, V.48, (2012), pp. 1111-1114.
S05-P07 The approach for reconstruction of GaSb:Te space crystal growing
Prostomolotov Anatoly1*, Verezub Nataliya1, Voloshin Alexey2, Nishinaga Tatau3
1Institute for Problems in Mechanics of Russian Academy of Sciences, 101-1 Vernadskogo ave., Moscow (Russia) 2Institute of Crystallography of Russian Academy of Sciences, 59 Leninskii ave., Moscow (Russia) 3Department of Electronic Engineering of University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo (Japan) *email: [email protected]
Quantitative X-ray topography of GaSb:Te crystal, grown during chinese unmanned space experiment [1] has showed a high structural perfection in its greater area, which corresponds to the crystallization of a rounded interface. At the same time, the defects in the field of a facet growth have been revealed after some time of the crystallization onset. The control of parameters during the growth process was absent. It was a reason for a reconstruction of the crystal growth history using a two-dimensional map of the measured Te concentrations in the crystal and mathematical modeling of the growth process, and taking into account of possible factors that influenced on the growth crystal characteristics [2]. The work has developed the mathematical models of different levels of complexity for calculating the crystallization process of GaSb:Te (from semi-analytic and 2D- hydrodynamic, describing a convective heat and mass transfer in the melt [3] to the conjugate thermal models that calculate the crystallization process in the real heating conditions and geometry of ampoule assembly). An applicability of analytical models (Barton Prima-Slichter – BPS and Ostrogorsky-Muller – OM) was analysed in comparison with 2D-modeling of convective impurity transport. It gave a possibility to consider BPS-model as a more accurate one, as well as offer its formula expressions for highly elongated melt areas and large velocities. It was shown the non-monotonic variation of macro-inhomogeneity impurity distribution on the crystallization interface (CI) upon the Grashoff number [3]. The influence of the heating conditions and the ampoule velocity on the crystallization rate and CI shape was investigated. It was studied the influence of main factors that influenced on the crystal quality: on Keff values, facet growth and transverse impurity inhomogeneity on the CI. The main factors were the thermal conditions (the values of the axial and radial temperature gradients, cooling rate), and the transverse ampoule size. It may be noted that the space experiment was carried out in conditions close to optimal. The realized values of the crystal growth rate have provided an acceptable level of radial inhomogeneity and temperature gradient – the relatively small size of the facet growth. The small diameter of the growth ampoule has provided a large "margin of safety" in relation of a convective influence on the heat transfer. The only deficiency of this experiment was the facet growth some time after the onset of crystallization. It was shown that the moment of the additional free surface formation near CI corresponds to the contact of the melt with the graphite insert. The non-coaxial contact relatively to the ampoule may be as a possible reason of a thermal asymmetry and a growth process disturbance. The facet growth was caused by such sharp change of the thermal conditions that led to the stronger thermocapillary effect and dramatically increasing the convection velocity. For Keff(Vmax) dependence it corresponds to a shift in the field of sharp change of Keff for the small variations of thermal parameters. It explains the observed features of the impurity distribution in the field of facet growth.
References: [1] Ge P., Nishinaga T., Huo C. et al., Microgravity Q., 3 2-4 (1993) 161. [2] Voloshin A.E., Nishinaga T., Ge P., Huo C., J. of Crystal Growth, 234 (2002) 12 [3] Prostomolotov A.I., Verezub N.A., Voloshin A.E., J. of Crystal Growth, 401 (2014) 111.
S05-P08 Influence of melt transparency on critical growth rate of sapphire V.V. Baranov*1, S.V. Nizhankovskyi 1
1Institute for Single Crystals, State Scientific Institution “Institute for Single Crystals” of National Academy of Sciences of Ukraine, Lenin 60, Ave, 61001, Kharkiv, Ukraine *email:[email protected]
The main factor which limits the rate of crystal growth is morphological instability (MI) of the crystallization front. One of the problems arising at investigation of the conditions of the occurrence of MI at the growth of high-temperature semitransparent sapphire is the necessity to take into account radiative supercooling of the melt in the vicinity of the crystallization front. This requires knowledge of the optical properties of the melt. In the present work there were established the degree of melt transparency in the vicinity of the crystallization front, as well as the influence of the melt transparency and the content of impurities on the critical growth rate of sapphire and Ti:sapphire crystals. The study was realized on the base of the analysis of the MI instability taking into account radiative heat transfer [1] and experimental data on the conditions of the growth of sapphire by the method of horizontally directed crystallization. The values of the absorption coefficients in the melt in the vicinity of the crystallization front (averaged according to Planck and P -1 R -1 Rosseland) were found to be L ≈13.5 сm and L ≈ 20 сm , respectively. The value of the melt supercooling caused by radiative heat transfer is ≈ 0.3-0.5 оС (Figure 1). It is shown that the critical growth rate of sapphire is close to the limiting case of the growth of absolutely pure sapphire (Сim = 0) (Figure 2, curves 2, 3). At the growth of Ti:sapphire with a high content of impurities MI is defined by the concentration supercooling of the melt, but the critical crystal growth rate also noticeably depends on the melt transparency (Figure 2, curves 1 ).
T,K 2324 2324
2322 S L 1 2320 2320
2 z,mm
0. 004 0. 003 0. 002 0. 001 0. 001 0. 002 4 3 2 112
Figure 1 Temperature distribution in the vicinity of the crystallization front at the growth of sapphire - (1) and Ti:sapphire ( Ti concentration in the melt is 1 mol. % ) - (2) .
Figure 2 Critical growth rate of sapphire, Сim=0. 05 mol. % - (2), Сim= 0 mol. % - (3) and Ti:sapphire (CTi=1 mol. %) - (1) depending on the value of the absorption coefficient in the melt averaged according to Planck (a) and Rosseland (b). References: [1]. Yuferev V.S., Chvoj Z., Kolesnikova E.N. // Journal of Crystal Growth. 1991. V.108 P. 367.
S05-P09 Growth of high optical quality ZnS single crystals by solid phase recrystallization technique at barothermal treatment
Eugeni Gavrishuk1, Vladimir Ikonnikov1*, Tatyana Kotereva1,Vladimir Pimenov1, Dmitry Savin1, Pavel Yunin2, Elena Mozhevitina3, Roman Avetisov3
1G.G. Devyatykh Institute of Chemistry of High-Purity Substances RAS, 49 Troponina St., Nizhny Novgorod (Russia) 2Institute for Physics of Microstructures RAS, Nizhny Novgorod (Russia), 3D. Mendeleyev University of Chemical Technology of Russia, Miusskaya pl.9, Moscow (Russia) *email: [email protected]
A large number of techniques is used for the growth of extra pure and high quality ZnS crystals which is very attractive as a laser material and component phosphors. The melt growth techniques do not allow producing extra pure ZnS, because of high contaminating action of setup materials at high temperatures. The chemical transport reactions technique is conducted at lower temperatures, but it contaminates the growing crystals by additional reagents. ZnS single crystals growing from vapor demonstrate an inconstant stoichiometry. In this situation a solid phase recrystallization (SPR) technique is regarded as a promising alternative for growing crystals of high purity and structural perfection [1]. It was successfully used to grow ZnSe, and ZnS single crystals of at ambient pressure close to atmospheric. The main disadvantages of this SPR technique is the formation of twins and the process duration, which amount up to 20 days at of 900 to 1100°C temperatures. It is difficult to apply higher temperatures due to zinc chalcogenides sublimation. An implementation of the SPR technique under isostatic pressure makes it possible to increase the temperature to 1300°C and to reduce the process time up to 1-2 days. In the research we conducted a solid phase recrystallization of polycrystalline ZnS under barothermal exposure (PAr = 90-200 MPa, T=1000-1200°C, t=22-44 hours). The polycrystalline ZnS with 10 microns average grain size produced by CVD technique was used as a raw material [2]. According to XRD the obtained ZnS samples after the barothermal processing composed of individual single crystals with a size of up to 15×15×6 mm. Nearby single crystals had at is very different orientation (parallel to the surface of various atomic planes), and slightly different orientation (disoriented relative to each other only a few degrees). The values of the rocking curve FMWH in the /2-scan for various single crystals varied in 0.04° to 0.7° range. The crystal's transmission in 0.35-14 microns range was close to the theoretical value. The purity as-grown crystals examined by ICP-MS technique was <10-4 wt.%. The main impurities (Fe,Cu) occurred from the gas-static setup. We reduced their concentrations in several times by placing ZnS samples in a tungsten foil container. The obtained results offer the challenge for growing ZnS and ZnSe perfect single crystal by a solid phase recrystallization under barothermal impact. The research was supported by the Russian Science Foundation grant N 15-13-10028
References: [1] R. Triboulet. Cryst. Res. Technol. 38(3-5) (2003) 215 – 224 [2] E. M. Gavrishchuk, V. B. Ikonnikov, D. V. Savin. Inorganic Materials 50(3) (2014) 222-227
S05-P10 Sapphire Shaped Crystals for Medicine
Kurlov Vladimir, Shikunova Irina*, Stryukov Dmitry
Institute of Solid State Physics (ISSP), 2 Academician Ossipyan str., 142432, Chernogolovka (Russia) *email: [email protected]
Excellent combination of mechanical and optical properties of sapphire together with chemical inertness and biocompatibility makes it an attractive structural material for medicine. We have developed new medical instruments and devices for laser photodynamic therapy and thermal therapy, laser surgery, fluorescent diagnostics, and cryosurgery based on sapphire crystals of various shapes with capillary channels in their volume grown by the EFG technique. Sapphire needle capillaries were developed as new laser waveguide introducers for delivery radiation into a tumor during interstitial laser photodynamic therapy, thermotherapy, and ablation of tumors. These needles allow one to increase the irradiation volume substantially, to obtain an optimal light or temperature distribution (Fig. 1) to simplify the design, and to eliminate a system for cooling the device. Sapphire scalpels with simultaneous incision and rapid real-time feedback analysis for on-line fluorescent diagnostics of tissues during surgery during surgical operation have been developed. The principle of the new system is based on the use of isolated capillary channels in the volume of the sapphire scalpel for introducing of quartz waveguides, Fig. 2. One of the waveguides is used for delivering the laser radiation directly to the narrow region of the cutting edge and local excitation of photoluminescence. Another one is used for catching and transfer of photoluminescence to spectrometer. The system for removal of brain tumors based on a sapphire multi-channel probe with demarcation of borders of a tumor by fluorescent diagnostics with simultaneous coagulation and aspiration was developed, Fig. 3. It carries out simultaneous laser coagulation for a hemostasis, tumor aspiration via the through channel of a sapphire probe, and also makes local optical measurements of properties of brain tissue for more exact and full removal of malignant tissue. Sapphire cryocooler-ligthguide for simultaneous or sequential laser therapy and cryoablation have been developed, Fig. 4. This allows to create the desired temperature gradient and to realize the fluorescent diagnostics of biological tissue during or after cryotherapy.
Figure 1. The geometry of light field in sapphire needle (OD 1.2 mm, ID 0.5 mm) combined with quartz fiber.
Figure 2. The sapphire blade with capillary channels of 0.5 mm diameter.
Figure 3. Sapphire multichannel probe for neurosurgery
Figure 4. Сryocooler-lightguide
S05-P11 Salt stains from evaporating droplets Noushine Shahidzadeh*1, Julie Desarnaud1, Marc Prat2, Daniel Bonn1
1University of Amsterdam, Institute of Physics,WZI, Science Park 904, 1098 XH Amsterdam (The Netherlands) 2Université de Toulouse, INPT, UPS, IMFT, Toulouse (Franc)
*email: [email protected]
In many applications such as the purification of pharmaceuticals, de-icing of airplanes, inkjet printing and coating applications, a phase change happens within the drop because of solvent evaporation, temperature changes or chemical reactions, which consequently lead to liquid to solid transitions in the droplets. Although the deposition pattern has been much studied for evaporating droplets of colloidal suspensions, very few studies exist of evaporating salt solutions, in spite of the fact that in many practical situations water contains dissolved salts, and that the much-studied colloidal systems are usually considered to be models for atomic systems. We therefore investigate the crystallization and resulting deposition patterns at microscale for drops of aqueous solutions of two different salts (NaCl and CaSO4) that evaporate on surfaces with different wettability and thermal conductivity. These salts are selected firstly because of their importance in many natural and industrial processes and secondly because they have different crystalline structures and precipitation pathways. Our results show that crystallization patterns of evaporating salt solutions are different from the stains reported for evaporating colloidal suspensions. This happens because during the solvent evaporation, the salts crystallize and grow. The resulting patterns of salt crystal stains are found to be predominantly controlled by the wetting properties of the crystal as well as the pathway of nucleation and growth, and are independent of the evaporation rate and thermal conductivity of the substrates.
Figure 1. Phase-contrast micrographs of the growth of CaSO4 polymorphs at the contact line for various contact angles θ of the droplet with the glass substrate: a)~5°; b) ~13°;c) ~30°; d) ~90°: rapid growth of gypsum crystals and remaining mesoscopic clusters1.
References: [1] N.Shahidzadeh, M.Schut, J.Desarnaud, M.Prat, D.Bonn, Scientific Reports 5, (2015),10335.
S05-P12 Crystal growth under high electric field: Analysis of the nucleation process
P. Hicher1*, R. Haumont1,2, R. Saint-Martin1, T. Baudin1, P. Berthet1
1 Equipe Synthèse, Propriétés et Modélisation des Matériaux, ICMMO, CNRS-UMR8182, Université Paris Sud, 15 rue Georges Clémenceau, 91405 Orsay Cedex, France 2 Laboratoire Structures, Propriétés et Modélisation des Solides, CNRS-UMR8580, Ecole Centrale Paris, Grande Voie des Vignes, 92295, Chatenay-Malabry Cedex, France
*e-mail: [email protected]
Single crystals of high quality and finely orientated are essential for the study of intrinsically anisotropic physical properties. Indeed, properties of interest such as ferroic properties are conditioned by the material’s structure, its chemical purity, crystallization quality and crystallographic orientation. During crystal growth, the crystallization interface plays a key role in the growth quality and orientation. Indeed, the crystallization front is the seat of mater diffusion and energy transfer. Therefore, in order to grow high quality single crystals, control over the growth interface is essential. Herein, we report first results on the effect of an applied external electric field on the first stage of crystal growth, the nucleation. A device of strong external electric field has been designed to fit in an optical mirror furnace. The interest of proceeding to crystal growth under an applied electric field resides in the fact that such an external field is able to perturb the growth interface and may, consequently, lead to a controlled crystallization front. Several works have shown that it is indeed possible to use the electric field as a motion force of crystallization which can, in some cases increase and, in other cases, decrease the nucleation rate regarding its effect on the activation energy of nuclei [1,2,3]. The purpose of this work is to better apprehend the effect of an external electric field on the nucleation stage of oxides materials growth with the aim to, at term, be able to promote an orientation of growth of interest with the use of an external electric field as an additional parameter to temperature and gas pressure. First results show that the applied external electric field acts upon the first stages of crystal growth in terms of grains’ number, size and orientation.
[1] W. Huang, S. Uda, S. Koh, Journal of Crystal Growth 307 (2007) 432-439 [2] R. Ghanasekaran, P. Ramasamy, Journal of Crystal Growth 79 (1986) 993-996 [3] D. Kashichiev, Journal of Crystal Growth 13/14 (1972) 128-130
SESSION 6
Mesocrystals and Nonclassical Crystallisation ⁄ Growth of Biological Materials and Biologically-Controlled Growth
Multi Scale Approach of the Bio Crystal Status and Growth in Mollusc Shells Alain Baronnet CINaM-CNRS & Aix-Marseille Université, Campus Luminy, 13288-Marseille cedex, France [email protected] The way living organisms proceed to build up their partly crystalline shell or skeleton is still an enigma for bio mineralogists, and there is yet no fully satisfying answer as to the crystal growth processes involved. However consensus is reached that we deal here with non classical crystallisation. Beyond the fascinating question, there is the challenge of finding a new way to nucleate and grow crystals. To constrain the possible growth mechanisms involved in shells it was first a high need of thorough characterization of the organo-mineral composite of the Ca-carbonate shell of some molluscs, the latter being considered as model cases of biomineralization [1]. We present here mainly photon and electron microscopy observations on marine and terrestrial gastropod and bivalve microstructures, made in presence of recognized and acceptable artifacts. The organo-mineral composite appears simultaneously at at least three levels of scale, with the smallest at the nanometer scale. Organic matter component may show up as a pore-filling gel, sheets, fibers and "nodes". The mostly crystalline component resembles the corresponding abiotic Ca-carbonate polymorphs regarding their crystal-chemical, diffraction and optical properties. However quasi atomic structure imaging by high-resolution transmission electron microscopy (HRTEM) shows locally considerable elastic 2+ 2- distorsions of the Ca - CO3 ionic columns, when in direct contact with fibrillar or sheet-like organic matter. Numerous cationic and anionic vacancies are also diagnostic of such biogenic carbonates and bulk dislocations are absent. Growth twinning may be present as in abiotic counterparts [2]. When averaged such crystalline matter appears as partly disordered, i.e., may be seen as intermediate between the perfectly crystalline state and the amorphous state. At the higher submicron scale, mostly crystalline, interconnected, granules are ubiquitous building units of hardest parts of the shell [3]. They arrange as linear chains (third- order lamellae of the cross-lamellar microstructure), sheets (nacreous layer) or may form 3-D microstructures (prismatic layer). Contiguous granules interpenetrate, strongly suggesting they were emplaced as a soft, i.e. non crystalline, material. In case of aragonitic fibers (e.g., land snails), growth twin planes propagate perfectly from granule-to-granule along the fibers which further supports that carbonate crystallisation takes place after granule emplacement and that crystallisation propagates across their contact. The growth mechanisms at work at the very border of the shell of farmed Crassostrea gigas are then reported to illustrate the dynamics of shell growth. Here bio crystals of the prismatic layer nucleate each already as a single crystal on a unique Ca-free organic nodule located on the periostracum. Crystalline but xenomorph nuclei grow first by granule addition according to a 2-D process until they meet, thus squeezing the organic wall between them. Then the tiling pattern is maintained and strengthened in each shell scale while the secreting mantle is "pulling" prisms normal to it. The smooth growth front, irrespective of local crystallographic orientations and microstructures, indicates a rate- and shape-controlling mantle acting very close to the shell when mineralizing (interstitial growth). Occasional morphological instabilities of prisms in spite of small growth rate support bulk diffusion-limited supply of Ca, and thus rather crystal growth from an hydrogel [4] than crystal growth from a conventional aqueous solution. At any stage of the shell development, the crystalline matter is found isolated from the surrounding by organic matter and resulting isolated compartment growth mechanisms are found the same for land or marine species. By the way, environmental signatures in a shell are not direct, as mitigated by the metabolism of the shell-bearing organism. The shell development of molluscs appears thus largely bio-controlled at any scale so that their species-specific shape be maintained.
References: [1] Addadi L., Joester D, Nudelman F, Weiner S. Chem. Eur., 12 (2006) 980. [2] Kobayashi I., Akai J. Jour. Geol. Soc. Japan, 100, 2, (1994) 177 [3] Baronnet A., Cuif J.P., Dauphin Y., Farre B., Nouet J. Min. Mag., 72, 2 (2008) 539 [4] Asenath-Smith E., Li H., Keen E.C., Seh Z.W., Estroff L.A. Adv. Funct. Mat., 22, 14 (2012) 2891
Bio-inspired Composite Crystals: Incorporation of nanoparticles in calcite and zinc oxide single crystal
1 2 2 1 Alex Kulak , Pengcheng Yang , Mona Semsarilar , Oscar Cespedes , Yi-Yeoun Kim1, Steven P. Armes2, Fiona C. Meldrum1*
1School of Chemistry, University of Leeds, Leeds, UK 2Department of Chemistry, University of Sheffield, Sheffield, UK
Composite materials based on inorganic host materials with well-defined structures and combined functions with guest inorganic components had been centre of most pursued advanced materials due to their extraordinary properties, which is origin from synergetic effects between the components. Many biominerals created in nature, showed this unique feature, where significant amounts of macromolecules and small molecules are intimately incorporated in single crystal domain, without disrupting the 3-D crystal lattice structures. The exceptional hardness and toughness of biominerals account for this structural architecture. In this work we present a facile one-pot method of the formation of novel heterostructures in which inorganic nanoparticles are homogeneously distributed throughout an inorganic single crystal matrix. Our strategy uses nanoparticles functionalised with diblock copolymers as a soluble crystal growth additive. We show that gold and magnetic nanopaticles can be incorporated in the crystals (calcite and zinc oxide) in the presence of suitable block-copolymers. The encapsulation of magnetite nanoparticles(MNP) and gold nanoparticles (GNP) into a single crystals is investigated aiming at producing crystals with new functions and properties. The encapsulation is achieved by precipitating calcium carbonate or zinc oxide in the presence of nanoparticles with their surfaces modified by various chemicals. Two different MNP were used, one with arylsulfonyl groups and another with alkylsulfonyl. It is shown that the level of incorporation in the host crystals depends strongly on the nature of crystal and organic fragment attaches to MNP. A good degree of encapsulation of MNP in the crystals is obtained. In the case of GNPs was used zwitterionic diblock copolymer.
Fig. 1: TEM image of a thin section through MNPs in calcite; insert: a high resolution TEM image showing the continuity of the crystal lattice around an embedded magnetite particle.
Optimization of Crystallization using Dialysis Combined with Temperature Control
Niels Junius1, Esko Oksanen2, Maxime Terrien3, Christophe Berzin1, Jean-Luc Ferrer1 and Monika Budayova-Spano*1
1Institut de Biologie Structurale UMR 5075 CEA-CNRS-UJF, 71 Avenue des Martyrs, Grenoble (France) 2European Spallation Source, P.O. Box 176, Lund (Sweden) 3Laboratory of Pulp and Paper Science and Graphic Arts, Grenoble INP-Pagora, Grenoble (France) *email: [email protected]
We have constructed a prototype of an integrated apparatus for the rational optimization of crystal growth by mapping and manipulating temperature-precipitant concentration phase diagrams [1]. Much instrumentation development in crystallization has concentrated on massive parallelization of experiments and reduction of sample volume per experiment to find initial crystallization conditions. Improving the size and diffraction quality of the crystals often requires decoupling crystal nucleation and growth. This in turn requires controlling variables such as precipitant and protein concentration, equilibration rate, temperature, that are all difficult parameters to control in the existing setups. The success of the temperature controlled batch method, of which the initial aim was to grow very large crystals for neutron crystallography [2,3], convinced us that the rational optimization of the crystal growth has potential in structural biology. Our approach differs from the current paradigm, since we propose serial instead of parallel experiments, exploring multiple crystallization conditions with the same protein sample. The sample is not consumed in the experiment and the conditions can be changed in a reversible fashion. A major feature of our instrument is the software integration that allows visualization of the crystals and in situ control of the temperature and composition of the crystallization solution. Rational crystallization optimization strategies presented here allow tailoring of crystal size, and diffraction quality, significantly reducing the time, effort and amount of expensive protein material required for structure determination. The goal of the presentation is to demonstrate that a thorough knowledge of the phase diagram is vital in any crystallization experiment. The relevance in selection of the starting position and kinetic pathway undertaken to control most of the final properties of the synthesized crystals is shown.
References: [1] Budayova-Spano M., Patent FR10/57354, UJF (2010) (Extension: EP117730945, US13821053, JP2013528746). [2] Budayova-Spano M., Dauvergne F., Audifren M., Bactivelane T., Cusack S., Acta Crystallogr, D63 (2007) 339-347. [3] Oksanen E., Blakeley M.P., Bonneté F., Dauvergne M.-T., Dauvergne F., Budayova-Spano M., J. R. Soc. Interface, 6 (2009) S599-S610.
Influence of shear rate and surface area on nucleation kinetics in aqueous solutions of glycine and urea reveals nonclassical nucleation mechanisms
Carol Forsyth, Danielle Trap, Jan Sefcik*
Department of Chemical and Process Engineering, University of Strathclyde, G1 1XJ, Glasgow, UK [email protected] Understanding crystal nucleation from solution is important for rationally designing and controlling manufacturing processes that involve crystallization. Both batch and continuous industrial crystallization processes typically involve fluid flow where supersaturated solutions and/or suspensions of growing crystals are pumped or agitated. It is well known that fluid shear can induce secondary nucleation and it has been also experimentally demonstrated that primary nucleation can be affected by fluid shear as well [1,2]. In order to gain further experimental evidence to facilitate improved understanding of effects of fluid shear on primary nucleation and underlying nucleation mechanisms, we investigated nucleation in aqueous solutions of glycine and urea under various flow conditions at a constant temperature. Solutions were prepared by nanofiltration followed by slow cooling and they were then subjected to either controlled fluid shear in Couette cells or agitation with magnetic stirring bars under isothermal conditions. The onset of nucleation was always associated with a rapid increase in turbidity, so induction times were readily obtained. The role of surface area was also studied by changing the diameter of the inner cylinder of the Couette cell. Due to the stochastic nature of nucleation, experiments were repeated numerous times and a statistical analysis was performed to show that the number of repetitions was sufficient for accurate trends to be deduced. In glycine solutions, the induction times of sheared solutions were considerably lower than unsheared solutions, while a great care was taken to avoid seeding in solution or at solid-liquid interfaces. This suggested that fluid shear had a profound influence on primary nucleation in these solutions. In sheared solutions, a large number of small crystals formed in close succession, causing solutions to rapidly go turbid, so it is proposed that shear enhanced the formation of a primary nucleus which then initiated extensive secondary nucleation [3]. Increasing the average shear rate was found to reduce the induction time in a power law relationship with an exponent of 0.98±0.1. This indicated that the total strain applied was important for control of nucleation. Increasing the surface area was found to notably decrease the induction times, which indicated that the surface also played an important role. In situ dynamic light scattering measurements showed that colloidal scale liquid-like clusters observed in mesostructured amino acid aqueous solutions [4] were increasing their mean size upon continued shearing of solutions. This is consistent with these mesoscale clusters (in the bulk liquid phase and/or at the solid-liquid interface) being involved in the primary nucleation pathway in this system as proposed recently [1,5], where larger clusters correlated with shorter nucleation induction times. In urea solutions, study of induction times showed that nucleation appeared to be enhanced by agitation and unstirred solutions had significantly longer induction times than stirred ones. Surprisingly, a significant fraction of magnetically agitated vials (about 20%) appeared to nucleate during the first few seconds of agitation, followed by the rest of vials over an extended period of time. This trend was further investigated and it was found that longer aging of solutions at a constant temperature resulted in a larger fraction of vials nucleating during the first few seconds of agitation. Since urea is a very fast growing system (with crystal growth rate about 1 mm/s under conditions studied), this was clearly not due to secondary nucleation, and it thus provides a strong indication of a nonclassical nucleation mechanism in this system. References: [1] Jawor-Baczynska, A., Sefcik, J., Moore, B. D., Crystal Growth & Design, 13 (2013), 470. [2] Liu, J., Rasmuson, A. C., Crystal Growth & Design, 13 (2013), 4385. [3] Forsyth, C., Mulheran, P. A., Forsyth, C., Haw, M. D., Burns, I. S., Sefcik, J., Crystal Growth &Design, 15 (2015), 94. [4] Jawor-Baczynska, A., Moore, B. D., Lee, H. S., McCormick, A. V., Sefcik, J., Faraday Discussions, 167 (2013), 425. [5] Jawor-Baczynska, A., Moore, B. D., Sefcik, J., Faraday Discussions, (2015), doi: 10.1039/C4FD00262H.
Infrared light-induced protein crystallization
Kowacz Magdalena*1, Marchel Mateusz1, Juknaitė Lina2, Esperança José M. S. S.1, Romão Maria João.2, Carvalho Ana Luísa.2, Rebelo Luís Paulo N.*1
1Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Av. da República, 2780- 157 Oeiras, Portugal 2UCIBIO - REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal *email: [email protected]; [email protected]
In this work we show that electromagnetic radiation in the infrared (IR) range can i) induce protein nucleation from a metastable solution and ii) support proper ordering of biomacromolecules into a crystal under conditions where, in the absence of radiation, only non-specific aggregation takes place. To uncover the underlying mechanism we have performed Fourier-transform Infrared Spectroscopy studies revealing that the IR radiation can enhance mutual correlations of water molecules in the protein hydration shell (makes protein interfacial water more structured). Our results indicate that IR light induces changes comparable to those brought about by lowering the temperature of water of hydration and thus encourages enhanced ordering of the water network. Furthermore, the exposure of the protein solution to the IR radiation exerts an effect similar to protein solubilisation (and native structure stabilization) by a buffer medium. The structured water layer effectively “melts” upon addition of high concentration of inorganic salt. The IR-induced mutual correlation of water molecules results in an ordered interfacial layer that is polarized which can give origin to attractive interactions between like-charged biomacromolecules and hence promote nucleation. Nevertheless, the structured character of the hydration shell should help keeping individual protein molecules separated in solution (association without coalescence) until the structure is destroyed e.g. by addition of salts. These features are of great practical importance for protein crystallization. Inducing attraction of protein molecules at low protein concentration should allow proteins to meet in space and find proper mutual orientation (often referred as a rate limiting step in crystallization) before the crowding in solution (e.g. in the course of vapour diffusion experiments) restricts geometrical rearrangements. Enveloping protein within a protective layer of structured water, supporting protein native state, should further facilitate steric adjustments before specific intermolecular contacts can form (following disruption of ordered surface water e.g. on increasing precipitant concentration). Therefore, our results indicate that IR radiation can be used to promote and kinetically control protein crystal formation. Examples are shown for both model as well as “real-case” proteins that are difficult to crystallize.
Figure 1. IR and temperature induced changes in FTIR spectra of protein solution and corresponding crystallization outcomes
Precursor-based bioinspired synthesis of magnetite nanocrystals
Mirabello Giulia1, Söğütoğlu Leyla-Can 1, Lendesr Jos J.M.1, Sommerdijk Nico A.J.M*1.
1Eindhoven University of Technology, Building Helix Het Kranenveld 14 P.O. Box 513 5600 MB, Eindhoven (Netherlands) *email: [email protected] Magnetite (Fe3O4) is a widespread magnetic iron oxide, encountered in many biological and geological systems [1]. It also has many technological applications, e.g. in magnetic data storage materials, inks, ferrofluids, scavengers in water purification, but also in magnetic resonance imaging and controlled drug delivery [2-4]. Its magnetic properties depend largely on the size and shape of the crystals, and at room temperature only 20-80 nm particles display single- domain ferrimagnetic behavior. In Nature, magnetotactic bacteria synthesize 30-140 nm magnetite crystals, magnetically and crystallographically aligned in chains, thereby using their magnetic properties for navigation in the Earth’s magnetic field [5]. While many biomineralization systems can be mimicked synthetically using additives and templates [6], achieving control over the nucleation and growth of iron oxides is difficult, as they are only poorly soluble in water, generally leading to polydisperse products. Nature’s strategy to overcome this issue is the use of precursor phases for efficient transport of material and controlled conversion into crystalline products [7]. Indeed, ferrihydrite (Feh) has been identified as a precursor in the magnetosomes of magnetotactic bacteria and the outer layer of chiton teeth [8-9]. In our work presented here, we studied two synthetic routes to magnetite in water and at room temperature, one starting from iron(II) through partial oxidation with potassium nitrate (KNO3) and one starting from iron(III) through partial reduction with cysteine (Cys). In both cases, we make use of precursor phases (white rust or Fe(OH)2 for partial oxidation, and ferrihydrite or Fe(OH)3 for partial reduction), from which the more stable magnetite is formed in a second step. Further, we employ a computer-controlled titration setup to keep the reaction pH and reactant addition rates under control. We thus aim at extending the control over aqueous magnetite formation by combining all these strategies. For the partial oxidation method, we show that is it possible to tune the crystal size of the final product by changing the initial iron concentration, from 11 nm to 148 nm by going from 0.5 mM to 40 mM iron(II). This correlation probably arises because the dimensions of the Fe(OH)2 precursor are affected similarly by the iron(II) concentration. In the partial reduction route, the Cys was used as a sequestrant and reducing agent for iron(III), which is present in solution or in the solid state as ferrihydrite. When the Cys is added to a solution of iron(III) and then the pH is increased to alkaline conditions, the final product is magnetite. In contrast, when the Cys solution is added to a solution containing Feh in the solid state, the Feh dissolves by forming a chelate complex with the Cys and then at alkaline pH goethite (α-FeOOH) is obtained. The presented results show that magnetite can controllably be formed in water and at room temperature, through various strategies, by combining precursor phases with controlled reactant titration.
Figure 1. TEM images of magnetite nanocrystals synthesized by partial oxidation at different iron concentrations. a) 40 mM iron concentration, crystal size 148 ± 33 nm; b) 10 mM iron concentration, crystal size 34 ± 9 nm; 0.9 mM iron concentration, crystal size 21 ± 5 nm. (scale bare 500 nm) References: [1] Author A., Author B., Author C., Journal, volume (year) page. (font: Times New Roman, size: 11, left aligned) [1] R. M. Cornell, U. Schwertmann, The iron oxides: structure, properties, reaction , occurrences and uses. (Wiley- VCH Verlag GmbH & Co. KGaA, 2003). [2] A.-H. Lu, E. L. Salabas, F. Schüth, Angewandte Chemie International Edition 46 (2007), 1222. [3] S. Laurent et al., Chemical Reviews 108 (2008) 2064. [4] C. T. Yavuz et al., Science 314 (2006) 964. [5]F. R. B. a. B. D.A., Contributions to Microbiology 16 (2009) 182. [6] A. Finnemore et al., Nat Commun 3(2012) 966. [7] D. Faivre, T. U. Godec, Angewandte Chemie International Edition 54(2015) 4728. [8] Baumgartner J. et al., Proc. Natl. Acad. Sci. U. S. A, 110 (2013), 14883. [9] Gordon L. M. et al., Angewandte Chemie International Edition 53(2014) 11506.
Co-processing of Metformin Hydrochloride with Hydroxypropyl Methylcellulose and Sodium Carboxymethlycellulose during Crystallization to Manufacture Extended Release Tablets
Erdemir Deniz*, Chang Shih-Ying, Wong Benjamin , Rosenbaum Tamar, Kientzler Donald, Wang Steve, Desai Divyakant, Kiang San
Drug Product Science and Technology, Bristol Myers Squibb, 1 Squibb Drive, New Brunswick NJ (USA) *email: [email protected]
Metformin with the dose range of 500 mg to 2550 mg is the first-line therapy for the treatment of type 2 diabetes. The main challenge is to deliver the dose range using fewer easy to swallow small size extended release tablets. In addition, the manufacturing process for extended release tablets is challenging due to poor compactibility of metformin. To improve metformin compactibility and reduce tablet size, a co-processing approach was explored. In this approach, metformin was dissolved in water (solvent) and release controlling polymers, hydroxypropyl methylcellulose (HPMC) and sodium carboxymethlycellulose (NaCMC), were suspended in acetone/ethyl acetate mixture (anti-solvent). Mixing of solvent and anti-solvent formed metformin crystals agglomerated with polymers. The agglomerates were filtered and dried using an agitated dryer. They were lubricated with magnesium stearate and compressed into tablets. We demonstrated that this process could accommodate higher drug load to achieve the target dissolution profile and bioequivalence, leading to reduced tablet mass and size. The intimate mixing of HPMC and NaCMC with metformin HCl through co-processing reduced the risk of segregation during downstream handling and tableting. Moreover, with the improved metformin-polymer agglomerate compactibility and flow, a direct compression method was feasible reducing the overall manufacturing cycle time.
Heterogeneous nucleation and growth of calcium phosphate films on mica sheets by vapour diffusion
Jaime Gómez Morales *, Cristóbal Verdugo Escamilla, Lourdes Vega Espinar, Jose Manuel Delgado López, José Antonio Gavira Gallardo,
1Laboratorio de Estudios Cristalográficos. IACT (CSIC-UGR), Avda. Las Palmeras, 4. 18100 Armilla (Spain) *email: [email protected]
Nucleation and growth of calcium phosphate on metallic substrates (mainly Ti and its alloys) is a subject of intensive research because of the importance of coated implants for load bearing applications in the orthopedic and dental fields. Few studies, however, have been carried out using non-metallic substrates. Besides its interest at a fundamental level, these studies may have also a biomedical relevance for the preparation of implants for non-load bearing applications, or as a model for phosphorus recovery from waste water, or else for the preparation of biomimetic functionalized surfaces with potential capability to induce the nucleation of protein crystals. In this work we propose for the first time the vapor diffusion sitting drop method [1] to deposit bioinspired calcium phosphate films on non-metallic substrates, i.e. mica muscovite. Later on the capability of these films to induce the nucleation of proteins will be assessed using lysozyme as model protein. Coated experiments have been carried out in a crystallization mushroom using 12 mica sheets immersed in droplets composed of 50mM Ca(CH3COO)2 and 30mM (NH4)2HPO4 (Ca/P=5/3). A 3 mL aliquot of a 40mM NH4HCO3 solution was used as source of NH3 and CO2 gases. Experiments lasted 1, 7, 14 and 21 days. Additionally, polyacrylic acid (PAA) was used as an additive. Characterization was performed by optical microscopy OM, XRD, FT-IR and SEM. Deposited calcium phosphate layers are composed of apatite nanocrystals (Ap) and octacalcium phosphate (OCP), with increased amount of OCP at higher crystallization times. In the presence of PAA deposited layers are composed of amorphous calcium phosphate (ACP). Preliminary results of lysozyme crystallization indicate that coated mica sheets induce heterogeneous nucleation and promote the growth along surface-liquid interface generating unexpected flat crystals.
Figure 1.Thin films composed of Ap nanocrystals and OCP produced by vapour diffusion method
References: [1] J. Gómez-Morales, J.M. Delgado-López, M. Iafisco A. Hernández, M. Prat, Cryst Growth Des.11 (2011) 4802. [2] G. Tosi, S. Fermani, G. Falini, J.A. Gavira, J. M. Garcia Ruiz, Cryst Growth Des.,11 (2011) 1542
POSTER
S06-P01 An Approach for Controlling Epitaxial Growth of Protein Crystal by Using Microfluidic Device
Masatoshi Maeki*1,2, Ashtamurthy Pawate3, Masakazu Sugishima4, Keiichi Watanabe5, Manabu Tokeshi1, Paul J. A. Kenis3, Masaya Miyazaki2
1Hokkaido University, 13 Kita 8 Nishi, Kita-ku, Sapporo (Japan) 2National Institute of Advanced Industrial Science and Technology (AIST), 807-1 Shuku, Tosu (Japan) 3University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana (U.S.A) 4 Kurume University School of Medicine, 67 Asahi-machi, Kurume (Japan) 5Saga University, 1 Honjo, Saga, (Japan) *email: [email protected]
Three-dimensional analysis of protein provides essential information to the field of drug discovery and elucidation of protein functions. However, generating high quality protein crystals is considered as a bottleneck in the structure determination process. A microfluidic device for protein crystallization has been reported as a useful tool to explore protein crystallization condition. We have also reported the potential of the microdroplet for controlling single crystallization of protein. In this study, we demonstrated an approach for controlling epitaxial growth of protein crystals by using microfluidic device. Two types of microfluidic devices were fabricated to confirm the effect of micro-space on the protein crystallization. The depth of crystallization chambers was 10 µm and 50 µm. Lysozyme, glucokinase from Pseudoalteromonas sp. AS-131 (PsGK), and heme oxygenase (HO) complex were used as model proteins. Lysozyme and HO-complex were crystallized in an incubator at 20°C. Protein crystallization experiment for PsGK was also performed in a cold room at 4°C. At first, we carried out protein crystallization experiments by conventional method. Figure 1 (a) shows the PsGK crystal prepared by conventional crystallization method and was aggregated significantly. On the other hand, the microfluidic-based crystallization method can produce single PsGK crystal in each crystallization chamber within the microfluidic device. However, the growth behavior of protein crystal was dramatically changed by depth of the crystallization chamber, as shown in Figure 1 (c) and (d). The rod-shaped PsGK crystal and plate-shaped PsGK crystal formed in 50 μm and 10 µm crystallization chambers, respectively. We also found that the same crystal face was preferentially grown by using 10 µm crystallization chamber. In case of lysozyme crystallization, the lysozyme crystals were grown along to the (1 1 0) face. For these results, we consider that the space limitation affects adsorption behavior of the protein molecules to the crystal surface and induces epitaxial growth of protein crystal. Consequently, our microfluidic-based approach provides a simple preparation method of the high quality protein crystals.
Figure 1. (a) PsGK crystal prepared by conventional method. (b) Microfluidic device used in this study. There are 24 crystallization chambers. (c) PsGK crystal formed in the 50 µm crystallization chamber. (d) PsGK crystal formed in the 10 µm crystallization chamber. Scale bar represents 200 µm.
S06-P02 Biogenic and non-biogenic struvite
Jolanta Prywer
Institute of Physics, Lodz University of Technology, ul. Wólczańska 219, 90-924 Łódź, (Poland) email: [email protected]
The investigations of biogenic and non-biogenic struvite are performed in relation to infectious urinary stone formation - struvite is the main component of this kind of stones. Biogenic struvite is formed in artificial urine in the presence of microorganisms Proteus mirabilis (P. mirabilis). Non- biogenic struvite is formed after addition of aqueous ammonia solution to the solution of artificial urine. Such an addition emulates real infection similar to those caused by P. mirabilis. Both biogenic and non-biogenic struvite crystals possess well developed crystallographic surfaces. However, only biogenic struvite shows very characteristic surface structure [1]. The structure of individual surfaces of biogenic struvite looks as if it was built from small crystallites. On the basis of Scanning Electron Microscopy micrographs gaps between small units from which the crystal is built may be identified, suggesting the porous nature of struvite. The size of the gaps is in the range from tens to hundreds of nanometres. Taking in account this size it may be stated that biogenic struvite is macroporous material. The internal structure revealed with the aid of Focused Ion Beam microscope demonstrates that the porosity is characteristic not only for the crystal surface but also for the volume of crystals [1]. The porosity is a unique feature of biogenic struvite. Biogenic and non-biogenic struvite differs from each other also by crystal morphology while the habit remains almost unchanged [2]. The differences in struvite morphologies of biogenic and non-biogenic struvite are explained by electrostatic action between bacteria and crystal surfaces and by the differences in relative growth rates of individual faces. In the presence of P. mirabilis struvite crystals grow with relative growth rates in narrower range compared with those growing in the absence of P. mirabilis [2]. Consequently, the growth in the presence of P. mirabilis gives struvite crystals more regular compared with those in the absence of bacteria. It is suggested that P. mirabilis cells mediate the struvite crystal formation by some physicochemical processes resulting in the homogeneity in morphology. Summarizing, biogenic struvite differs substantially from non-biogenic struvite. This means that P. mirabilis are not only passive centres of nucleation, but actively mediate in growth processes.
Figure 1. Biogenic (a) and non-biogenic (b) struvite. Scale bar: 10 m.
References: [1] Prywer J., Torzewska A., Płociński T., Urological Research, 40 (2012) 699–707. [2] Sadowski R. R., Prywer J., Torzewska A., Cryst. Res. Technol. 49 (2014) 478–489. The work was supported by the National Science Centre (Poland), Project No. 2013/11/B/ST3/03871.
S06-P03 Influence of tetrasodium pyrophosphate on struvite and carbonate apatite formation
Marcin Olszynski*1, Jolanta Prywer1, Ewa Mielniczek-Brzóska2
1Institute of Physics, Lodz University of Technology, ul. Wólczańska 219, 93-005 Łódź (Poland) 2Institute of Chemistry, Environmental Protection and Biotechnology, Jan Długosz University of Częstochowa, ul. Armii Krajowej 13/15, 42-200 Częstochowa (Poland)
*email: [email protected]
Struvite and carbonate apatite (CA) are the main components of the so-called infectious urinary stones. This kind of stones is formed when the urinary tract is colonized by bacteria producing urease. The presence of urease in urine causes the series of chemical reactions resulting in increase in pH and creation of supersaturation conditions for struvite and CA precipitation. Treatment of infectious urinary stones is still a medical problem not fully solved. Modern treatment procedures for infectious urinary stones do not bring completely positive clinical responses and, additionally, the recurrence after treatment is on the level of 50% [1]. For these reasons, in recent years many studies on the effect of different substances on the formations of struvite and CA have been undertaken [2, 3]. The main aim of these studies is to find substances which potentially can improve the effectiveness of treatment and decrease of recurrence level of infectious urinary stones. In the present research we focus on the effect of tetrasodium pyrophosphate (abbreviated as NaPP) on the nucleation and growth of struvite and CA in the environment of artificial urine. The main goal of this research is to determine the effects of NaPP on the course and effectiveness of precipitation processes occurring in the urine and evaluate the potential application of NaPP as a inhibitor of infectious urinary stone formation. Our spectrophotometric results supported by microscopic observations clearly show that the increasing concentration of NaPP causes the delay of struvite nucleation and for a sufficiently high concentration the crystallization processes are completely stopped. However, the presence of NaPP leads to easier precipitation of amorphous phases e.g. CA. These results are explained based on the chemical speciation analysis.
Figure 1. Struvite (arrow 1) and CA (arrow 2) formed in the solution of artificial urine in the absence (a) and presence of NaPP (b). Scale bar:50 µm. Acknowledgements This work has been supported by the National Science Centre (Poland), Grant No. DEC- 2013/11/B/ST3/03871.
References: [1] L. Benramdane, M. Bouatia, M.O.B. Idrissi, M. Draoui, Spectrosc. Lett. 41 (2008) 72–80. [2] J. Prywer, M. Olszynski, J. Cryst. Growth, 375 (2013) 108-114. [3] C.K. Chauchan, M.J. Joshi, Urol. Res. 36 (2008) 265-273.
S06-P04 Investigation of bacterial factors responsible for aggregation process of carbonate apatite
Jolanta Prywer1, Rafal R. Sadowski*1, Agnieszka Torzewska2
1Institute of Physics, Lodz University of Technology, ul. Wólczańska 219, 93-005 Łódź (Poland) 2Department of Immunobiology of Bacteria, Institute of Microbiology, Biotechnology and Immunology, University of Lodz, ul. Banacha 12/16, 90-237 Łódź (Poland) *email: [email protected]
The investigations are performed in relation to infectious urinary stone formation. This is because that carbonate apatite, CA, is one of the main component of this kind of stones. Infectious urinary stones are formed when urinary tract is infected by microorganisms producing urease, mainly Proteus mirabilis (P. mirabilis). Even in the case of healthy person it may happen that some phases may be formed within urinary tract due to high supersaturation of appropriate species in urine. Usually, the formed phases are small enough (less than 2 µm) to excrete out the urinary tract, without causing damage of the epithelial cells. Therefore, it seems that the nucleation and the preliminary growth process are not the most important mechanisms leading to urinary stone formation. Urinary stones cause problems when precipitating phases became large enough to retain inside the urinary tract. Therefore, the aggregation is suspected to be one of the primary causes for urinary stone formation. CA is present as an amorphous precipitate and does not form crystals of defined morphology. It can easily aggregate with each other and with other components of the infectious urinary stones. The aggregation of particles precipitating from solutions is governed mainly by surfaces charges characterized by zeta potential. In our previous work [1] zeta potential of CA, struvite (other component of urinary stone) and bacteria have been measured and on this basis their aggregation in artificial urine have been studied. On the basis of the results it is stated that from these three components CA has the greatest ability to aggregate [1]. We have also observed an increased aggregation process in the presence of bacteria. This results suggest that some bacterial factors are responsible for increased aggregation of CA. Therefore, the aim of the current studies is to analyze an influence of some bacterial factors on the precipitation of CA and its aggregation. In particular, bacterial lipopolysaccharides (LPS) - the major outer surface membrane components of P. mirabilis - are chosen to verify their ability to increase the aggregation of CA. The sizes of CA aggregates formed without bacteria but for different concentrations of LPS are compared with the sizes of CA formed in the presence of bacteria. We also present particularly design experiment in which polystyrene latex beads, of dimensions close to the dimensions of bacteria, are overcoated with LPS and in this way they mimic the presence of bacteria in the solution of artificial urine. The results of our investigations give new and interesting findings.
Acknowledgements This work has been supported by the National Science Centre (Poland), Grant No. DEC- 2013/11/B/ST3/03871.
References: [1] Prywer J., Sadowski R. R., Torzewska A., Crystal Growth & Design 15 (2015) 1446-1451.
S06-P06 Prenucleation clusters – quatarons – and crystal growth
Askhabov Askhab
Institute of Geology of Komi SC UB RAS, Syktyvkar (Russia), [email protected] The situation with relatively stable existence of prenucleation clusters in crystal-forming media after long enough discussions of last years has considerably changed [1]. It is already recognized that formation of nuclei occurs through such clusters (the so-called two-step [2] or quataron [3] mechanism of nucleation). However till now that fact that growth of crystals also occurs by means of such clusters (the quataron model of growth of crystals) is practically ignored. This model acts as alternative to two known concepts of crystals formation, confronting during all 20th century. We mean the so-called Kossel concept usually named classical according to which crystals grow by joining of separate atoms, ions, molecules, and Balarev concept of nonclassical growth in which the basic building units are already formed crystalline particles (microblocks). The essence of the quataron concept, we develop, consists in that at growth of crystals the basic building units are special pre-crystallization clusters of "hidden" phase named quatarons [3]. At that quatarons owing to specific character of their structure and properties form a special form of the atomic-molecular organization of matter in the nanoworld. Quatarons, despite weak binding energies (mainly, van der Waals bonds) keep their integrity, but represent dynamic structures. In this they are similar to structureless molecules (clusters) of 4He3 [4]. In the process of increase in the sizes (change of number and type of bonds between atoms) quatarons evolve from almost structureless to more or less ordered objects. At establishing of chemical bonds between atoms, quatarons form rigid structures (quatarons of carbon, for example, are transformed into fullerenes [5]). Easiness of change of distances between atoms and angles of bonds between them, characteristic of quatarons, makes quatarons ideal building units. They practically without resistance can join any faces of a crystal and reconstruct on them. Meanwhile the most probable form of reorganization of quatarons on a growing face of a crystal is the formation of two- dimensional nuclei. It is specially noted that only quataron concept operates with nonequilibrium structural units at description of crystals growth, the process, in turn, is possible only in nonequilibrium conditions, this being one of the advantages of the quataron concept. At the same time, giving preference to the quataron mechanism of crystals growth, we cannot exclude multi-route character of this process. In the growth of crystals both separate atoms (ions), and molecular complexes, and substructural cluster units, and three-dimensional nuclei, and crystal blocks can take part. This work is supported by RFBR (14-05-00592а) and Grant of the President of the Russian Federation for support of Leading Science School (SC-4795.2014.5). References [1] Gebauer A. et al. Chem. Soc. Rev., 3 (2014) 43 2348-2371. [2] Vekilov P. Nanoscale, 2 (2010) 2346-2357. [3] Askhabov A. Proc. of Russ. Miner. Society, 4 (2004) 133 108-123. [4] Voigtsberger J. et al. Nature Comm. (2014) 5:5765 doi: 10.1038/ncomms.6765. [5] Askhabov A. Physics of the Solid State, 47 (2005) 6 1186-1190.
SESSION 7
In-situ Monitoring ⁄ Control of Crystal Growth Processes ⁄ Crystal morphology
Mechanistic insights into the early stages of crystallization of rare-earth carbonates
Rodriguez-Blanco, Juan Diego *1, Dideriksen, Knud1, Tobler, Dominique J.1, Sand, Karina K.2, Vallina, Beatriz3, Benning, Liane G.3,4, Stipp, Susan1
1Department of Chemistry, Nano-Science Center, University of Copenhagen, Copenhagen (Denmark) 2Lawrence Berkeley National Laboratories, Berkeley, California (USA) 3School of Earth and Environment, University of Leeds, Leeds (United Kingdom) 4Research Center for Geosciences, GFZ, Interface Geochemistry Section, Potsdam, Germany *email: [email protected]
Rare-earth element (REE) carbonates are important compounds that are usually found in carbonatite deposits (e.g., Bayan Obo, China; Mountain Pass, USA). Their consumption is considered an economic indicator because there is currently a strong demand for several REE (e.g., La, Nd, Eu, Dy) and this demand is expected to increase even more in the next decades. Two of the most important minerals in carbonatite deposits are lanthanites (REE2(CO3)3·8H2O) and bastnaesites (REE(OH,F)CO3), which include La, Ce, Pr, and Nd as major elements but also often traces of heavier rare-earth elements (e.g., Sm, Eu, Dy). Most research to date has focused on the structural determination and crystal chemistry of natural samples. However, there is little information about the crystallisation mechanisms of these minerals, the mobility and fate of the REE during their formation and the factors governing mineral stability. Do REE-carbonates crystallise in the same way as other divalent metal carbonates (e.g., Ca2+, Mg2+ [1]), through the breakdown of a nanoparticulate amorphous precursor? Or do they form through oriented attachment of nanocrystalline particles as for other salt systems (e.g., CaSO4 [2])?
To answer these questions, we applied UV-Vis spectrophotometry combined with synchrotron- based pair distribution function (PDF) analysis, Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD), to quantify changes in the REE3+-bearing carbonate local structure, composition, stability and crystallization pathways. Our results revealed that all REE3+ carbonates form from amorphous precursors at ambient temperature and the ionic potential of the REE3+ cation controls the hydration, precursor lifetime and the crystallisation kinetics of the REE3+ carbonates. Furthermore, PDF results confirmed short range ordering (<15 Å) and showed that the local structure differed depending on the REE3+ cation. Our new data identify the parameters that kinetically control the crystallisation of REE-bearing carbonates from solution, providing critical information to help with prospecting approaches to locate new REE deposits, reprocessing ores or recycling materials that contain REE to enhance recovery.
References: [1] Rodriguez-Blanco J.D., Shaw S., Benning L.G. Nanoscale, 3 (2011) 265-271. [2] Van Driessche A.E.S., Benning L.G., Rodriguez-Blanco J.D., Ossorio M., Bots P., García-Ruiz J.M. (2012) Science, 336 (2012) 69-72.
From Amino Acids to Cements: Crystallization Studied by CLASSIC NMR
Hughes, Colan E.1*; Williams, P. Andrew1; Keast, Victoria L.1; Edwards-Gau, Gregory R.1; Charalampopoulos, Vasileios G.1; Harris, Kenneth D. M.1; Gardner, Laura J.2; Walling, Sam A.2; Bernal, Susan A.2; Provis, John L.2
1School of Chemistry, Cardiff University, Park Place, Cardiff, CF10 3AT (U.K.) 2Department of Materials Science and Engineering, University of Sheffield, Mappin Street, Sheffield, S1 3JD (U.K.) *email: [email protected]
The CLASSIC (Combined Liquid- And Solid-State In-situ Crystallization) NMR technique [1] has been developed recently to monitor the evolution of both solid and liquid phases as a function of time during crystallization. By using NMR methods that selectively detect different motional regimes, the technique achieves essentially simultaneous monitoring of NMR spectra of both the crystallization solution and the crystalline products (including transformations of the solid phase). Variants of this strategy have been applied to study a range of crystallization systems, including amino acids (both proteinogenic and aminobenzoic acids), phosphine oxides, co-crystal systems (both stoichiometric and solid solutions) and cements. These studies have led to new insights on polymorphic evolution, discovery of hitherto unknown intermediates in crystallization pathways, understanding of the pre-nucleation state of solutions and knowledge of crystallization kinetics [2]. The versatility of the technique will be illustrated by studies of the competitive growth kinetics of polymorphs of glycine (Figure 1a) and the formation of distinct aluminium sites during the setting of a hydraulic cement (Figure 1b). The results for glycine demonstrate that the presence of a small, undissolved amount of the thermodynamically stable but slow-growing γ polymorph has a complex effect on crystallization from water. Whilst the formation of the α polymorph is observed as anticipated, the growth kinetics are affected significantly by the presence of the γ polymorph. For the calcium aluminate cement, the observation that different types of aluminium coordination site are present at different stages of the hydration reaction allows known physical changes in the formation of this type of cement to be understood on the basis of the chemical changes occurring.
Figure 1. (a) 13C NMR peak intensities for the (red) and (green) polymorphs of glycine during crystallization from 27 H2O by slow cooling. (b) Solid-state Al NMR spectra recorded as a function of time during the hydration reaction of calcium aluminate cement. Spectral evolution over 12 hours is shown.
References: [1] Hughes, C. E., Williams, P. A., Harris, K. D. M. Angew. Chemie Int. Ed., 2014, 53, 8939-8943. [2] Hughes, C. E., Williams, P. A., Keast, V. L., Charalampopoulos, V. G., Edwards-Gau, G. R., Harris, K. D. M. Faraday Discuss., 2015, in press [DOI: 10.1039/C4FD00215F]
An Investigation into the Particle Growth Pathway of Precipitated Fenofibrate
Tierney, Teresa B.1, Rasmuson, Åke C.1,2, Hudson, Sarah P.*1
1Synthesis and Solid State Pharmaceutical Centre, Materials and Surface Science Institute, Chemical and Environmental Science, University of Limerick, Limerick, Ireland. 2Department of Chemical Engineering and Technology, KTH Royal Institute of Technology, Stockholm, Sweden *email: [email protected]
Nano to small-micron sized particles of the hydrophobic drug, fenofibrate, were prepared by controlled crystallisation in order to influence its dissolution behaviour. An antisolvent precipitation process successfully generated nanoparticles (200-300 nm) which matched the size and dissolution behaviour of a commercial wet-milled nanoformulation of the drug, but by a more energy/time/cost efficient approach. Although the nanoparticle formation process was straightforward, retaining the size of the freshly precipitated nanoparticles in suspension and during isolation was challenging. Additives were employed to temporarily stabilise the nanosuspension, and extend the time window for nanoparticle isolation. Precipitated particles were isolated by immediate freeze-drying, but stresses which occur during the drying process, were found to destabilise the fragile nanoparticle system. Freeze-drying did however induce an interesting growth pathway, whereby nanoparticle- based aggregates gradually evolved into uniform and highly-defined parallelepiped structures of ~4µm. While oven-drying produced similar structures, a visually different growth pattern was observed, due to faster kinetics at elevated oven-drying temperatures. Time-resolved morphological analysis of the freeze-dried particles initially induced speculation of a non-classical ‘mesocrystal’ growth pathway. However, an investigation of the electron diffraction patterns and cross-sectional inner surfaces of particles contradicted this initial hypothesis.
Figure 1. Two proposed particle growth pathways for precipitated, freeze-dried fenofibrate
Growth of nanostructured carbon materials by Supersonic Molecular Beams of C60 on Cu studied by Surface Electron Spectroscopies
Aversa Lucrezia*1, Tatti Roberta1, Taioli Simone2,Garberoglio Giovanni2, Speranza Giorgio3, Cavaliere Emanuele4, Gavioli Luca4, Iannotta Salvatore5, Verucchi Roberto1
1IMEM-CNR Trento, Via alla Cascata 56/C, Povo (TN) (Italy) 2ECT* and TIFPA, Via Sommarive 18, Povo(TN) (Italy) 3CMM-FBK, Via Sommarive 18, Povo (TN) (Italy) 4Università Cattolica del Sacro Cuore, Via Musei 41, Brescia (Italy) 5IMEM-CNR, Parco Area Delle Scienze 37/A, Parma (Italy) *email: [email protected]
Fullerene (C60) is a molecule fully formed of carbon that can be used, owing to its electronic and mechanical properties, as precursor for the growth of carbon-based materials. The interaction of C60 particles, using Supersonic Molecular Beams that are characterized by a tunable translational kinetic energy, with metal surfaces can produce different processes starting from chemisorption up to cage opening or breaking, either thermally or kinetically, opening the way to the formation of nanostructured carbon materials. Having in mind the primary target, i.e. the strong interaction with the surface and formation of new carbon materials, we achieved the synthesis of graphene, single layer thin film on Cu(111) surface kept at 645°C by using C60 precursor and the Supersonic Molecular Beam Epitaxy (SuMBE) approach. This result has never been observed in the same experimental conditions in molecular beam epitaxy experiments (MBE) and has been investigated by experimental and theoretical studies, paving the way for graphene synthesis on other metal substrates even at lower processing temperatures. In this work we present the investigation of C60 impacts on copper at different kinetic energies with the aim of breaking it and forming carbon- based materials. Using a variety of electron spectroscopy (XPS, UPS, AES) and microscopy techniques (STM), Raman characterization and first-principles simulations, we discuss the chemical-physical mechanisms on which thermally-assisted graphene growth by SuMBE is achieved.
Grain growth competition in directionally solidified multi-crystalline silicon studied with in situ X-ray imaging techniques
Thècle Riberi-Béridot*1, Nathalie Mangelinck-Noël1, Amina Tandjaoui2, Guillaume Reinhart1, Maria Tsoutsouva1, Gabrielle Regula1, José Baruchel3
1Aix-Marseille Université, CNRS, IM2NP UMR CNRS 7334, Campus Saint Jérôme, case 142, 13397 Marseille Cedex 20 (France) 2Laboratoire de Mécanique de Lille (UMR CNRS 8107), Ecole Centrale de Lille, CS-20048, F-59651 Villeneuve d’Ascq Cedex (France) 3ESRF, 71, avenue des Martyrs, CS40220, 38043 Grenoble Cedex 9 (France) *email: [email protected]
Crystalline silicon (Si)-based photovoltaic cell technology is well-established and currently represents about 90% of the world PV market. Grain structure, impurities and defects induced during the crystal growth process, have a major impact on the final PV efficiency. However, the involved fundamental mechanisms that define the final grain structure are still not fully understood preventing an efficient and reproducible control of the silicon crystallization. Experiments based on the Bridgman solidification technique with X-ray imaging are performed. The unique experimental device developed allows following in-situ and in real time the formation of the grain structure. During the solidification, two imaging characterisation techniques using X- ray synchrotron radiation at ESRF (Grenoble, France) are combined: X-ray radiography and X-ray Bragg diffraction topography. The X-ray radiography method brings information on the morphology and kinetics of the solid/liquid (S/L) interface. The X-ray Bragg diffraction topography gives additional information about the evolution of the grain shape and structure, the defect formation and the local level of crystal distortion during growth (Figure 1). Additionally, Electron Backscattered Diffraction (EBSD) has been used to reveal the crystalline orientations of the grains and the twin relationships. 500 µm Solid-liquid interface
(a) (b) (c) (d)
Figure 1. X-ray imaging topography during the solidification (cooling rate: R = 0.2 K/min at t0 to R = 4 K/min at t0 + 1200 s, temperature gradient: G = 20 K/cm) of a Si (6N) sample. Zoom on a diffraction spot at (a) t0 + 180 s; (b) t0 + 420 s; (c) t0 + 900 s; (d) t0 + 1246 s.
New grains formed during growth have two main origins: random nucleation and twinning. It is demonstrated that the solidified samples are dominated by ∑3 twin boundaries formed by twinning on {111} facets. Moreover, thanks to the in situ characterization of the growth, it is shown that twins nucleate on {111} facets located at the sides of the sample (Figure 1) and at grain boundary grooves. The occurrence of multiple ∑3 twins during growth prevents the initial grains from developing all along the sample, and twin boundaries with higher order coincidence site lattices can form at the encounter of two grains in twin position. The grain competition phenomenon following nucleation and twinning acts as a grain selection mechanism leading to the final grain structure.
Evaporation Crystallization of Glycine J. Puranen, M. Louhi-Kultanen Laboratory of Separation Technology, School of Engineering Science, Lappeenranta University of Technology; P.O. Box 20, FIN-53851 Lappeenranta Finland [email protected]
For many decades, understanding and controlling of solution crystallization and crystal polymorphism have been areas of intensive research. In order to ensure that the correct polymorph is produced, the ability to monitor and control the crystallization process and polymorph transformation is critical. Amino acids are widely used as model compounds because of their well-known physical properties and their ability to crystallize in a range of polymorphs. The simplest amino acid is glycine (NH2CH2COOH), which is found in various proteins and enzymes. Glycine crystallizes in three polymorphic forms at atmospheric pressure: α, β and γ, from which the β form is a metastable form. The present study focuses on the evaporation crystallization of glycine from aqueous solutions and water-ethanol mixtures with different ratios at controlled conditions (i.e. aerodynamic conditions, temperature, air humidity and mass transfer between the gas and liquid) with an evaporation chamber equipment developed especially for polymorph screening. This approach provides more precise analysis results for polymorph screening and evaporation rates, as well as enhancing control of solvent evaporation at the desired temperature. Evaporation crystallization experiments were carried out with the evaporation chamber equipment at 40 °C, 50 °C and 60 °C with constant flow velocities of 0.2 and 0.3 m/s at ambient pressure and temperature. In this study, the obtained polymorphs of glycine crystals (analyzed with X-Ray powder diffraction and optical microscopy) and the empirical evaporation rates are assessed and evaluated. The influence of the evaporation rate of the solvent and solvent mixtures on the crystal formation and crystal structure of the glycine is also discussed.
Polymer versus monomer action on the growth and habit modification of sodium chloride crystals
E. Townsend1, W.J.P. van Enckevort1, J.A.M. Meijer2, E.Vlieg1
1Radboud University Nijmegen, The Netherlands; 2Akzo Nobel B.V., Deventer, The Netherlands
In this investigation, we have looked into the use of polymers and monomers as habit modifiers and anticaking agents for sodium chloride. We show that amide functional groups cause {111} faces to propagate on sodium chloride crystals and that polymer amides give a 1-2 orders of magnitude greater effect than the corresponding monomers on the habit modification of sodium chloride. We have also shown that the alcohol functional group does not have an effect on the surface or habit modification but that, when in a polymer form, leads to macrostep formation and acts as a nucleation inhibitor. The latter also holds true for other polymers that we have also tested. Finally, we found that no amino acids, apart from glycine, have an effect on the morphology of NaCl crystals.
Application of LPE method for producing of high-performance scintillating screens based on the single crystalline films of multicomponent garnets
Yu. Zorenko1,2*, T. Zorenko1,2, V. Gorbenko1,2, T. Voznyak2, O. Sidletskiy3, Ya. Gerasymov3, A. Fedorov5
1Institute of Physics, Kazimierz Wielki University in Bydgoszcz, 2 Powstańców Wielkopolskich str., 85090 Bydgoszcz (Poland)
2Electronics Department, Ivan Franko National University of Lviv, 5 Dragomanova str.,79017 Lviv, Ukraine
3Institute for Single Crystal NAS of Ukraine, 60 Lenin av., 61178 Kharkiv (Ukraine) 4Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland) *email: [email protected]
The liquid phase epitaxy (LPE) play a key role at the obtaining the high–density single crystalline film (SCF) scintillators based on different oxide compounds [1, 2]. Most hot topic today is the creation of SCF scintillation screens in 2D/3D detectors used for micro-imaging applications under excitation by X-rays or synchrotron radiation [2]. This report presents our achievements in the development of new types of SCF scintillators based on the A3-xAl5-yGayO12:Ce garnet compounds; A=Gd, Lu, Tb and their combination at x=0÷3.0 and y=1.5÷3.5, using the LPE method from PbO and BaO based fluxes onto Y3Al5O12 and Gd3Al2.5Ga2.5O12 (GAGG) substrates. The bulk crystals of multicomponent garnets are now on the top list of most efficient oxide scintillators with the light yield (LY) up to 60000 Ph/MeV [3]. Therefore, creation of SCF analogues of such garnets is now very actual task in frame of producing scintillation screens for X-ray imaging with submicron spatial resolution [2]. We report in this work optimised content and excellent scintillation properties of SCF scintillators based on the Gd3-xLuxAl5-yGayO12:Ce, Gd3Al5-yGayO12:Ce and Tb3-xGdxAl5-yGayO12:Ce multicomponent garnets grown by LPE method. Namely, the Gd1.5Lu1.5Al2.75Ga2.25O12:Ce and Gd3Al2.5Ga2.5 O12:Ce SCF, grown from BaO based flux, shows comparable LY with high-quality Cz grown bulk crystals analogues but faster scintillation decay response. These SCF possesses the highest LY values from all obtained in our group garnet SCF scintillators exceeding by at least 1.6-1.7 times the LY of best samples LuAG:Ce SCF analogues, grown from PbO based flux. At the same time, the quality of these SCF scintillators is strongly influenced by the high-viscosity of BaO based melt. The LY of SCF of Gd1.5Lu1.5Al3-2.75Ga2-2.25O12:Ce and Gd3Al3-2.75Ga2-2.25O12:Ce garnets, grown from PbO based flux, is notable lower (by at least 2.5 and 6.5 times, respectively) than LY of their analogues grown from BaO flux due to strong quenching influence of Pb2+ flux related impurity. Meanwhile, these SCF also possesses very fast scintillation response. With the aim of enhancing the energy transfer from the garnet host to the Ce3+ ions, the SCF of the Tb3Al5-yGayO12:Ce and Tb3-xGdxAl5-yGayO12:Ce garnets were crystallized by the LPE method onto GAGG substrates and the luminescent and scintillation properties of these SCFs were studied as well. Due to the efficient Tb3+Ce3+ and Gd3+Tb3+ Ce3+ energy transfer in the mentioned garnet matrices, we have observed strong increasing the LY of SCFs of these compositions. Namely, the LY of Tb3Al3Ga2O12:Ce and Tb1,5Gd1,5Al3 Ga2O12:Ce SCF, grown from PbO-based flux are equal to 1.2 and 1.5 with respect to LuAG:Ce SCF and comparable with the LY of Gd3Al2Ga3O12:Ce and Gd3Ga2.5 Al5O12:Ce bulk crystals. To our knowledge, these are the highest LY values obtained in SCF scintillators so far, prepared from PbO based flux [4]. The role of Ga3+ co-doping in the improvement of the efficiency energy transfer in Tb3-xGdxAl5-yGayO12:Ce matrixes was discussed. The comparison between the luminescent and scintillation properties of A3-xAl5-yGayO12:Ce SCF; A=Gd, Lu, Tb, grown from PbO and BaO fluxes was performed as well. References: [1] Yu. Zorenko, V. Gorbenko, T. Martin, P.-A. Douissard, , et all, Radiation Measurements 56 (2013) 415. [2] Т. Мartin, A. Koch, Journal of Synchrotron Radiation, 13 (2006) 180. [3] K. Kamada, T. Endo, K. Tsutumi, J. Pejchal, M. Nikl, et all., Cryst. Growth Des., 11 (2011) 4484. [4] P.-A. Douissard, T. Martin, F. Riva, Y. Zorenko, e. all, Proc. SCINT2015 conference, San-Francisco, 2015.
This work was realized within the Polish NCN No 2012/07/B/ST5/02376 and Ukrainian SL-20F projects.
POSTER
S07-P02 New crystallizer design for scaling salts crystal growth research avoiding crystal attrition
Torres-Serrano, Víctor Manuel*1,2, Wagterveld, Martijn1, Miedema,Henk1, Witkamp, Geert-Jan1,2
1Wetsus, European Centre of Excellence for Sustainable Water Technology, P. O. Box 1113 8900 CC, Leeuwarden (The Netherlands) 2Department of Biotechnology, Delft University of Technology, Julianalaan 672628 BC, Delft (The Netherlands) *email: [email protected], [email protected]
A special glass-made reactor design is used for the study of crystallization of calcium carbonate and other scaling salts offline and on-line. Changes in the (hydrodynamic) regime in the reactor, and the presence of foreign (organic and inorganic) substances, including fresh and recycled antiscalants on scaling salts crystal growth are investigated. The cylindrical crystallizer has a draft tube inside and it is special bottomed-shaped. This configuration helps to keep the solution in motion (in circles) very gently inside the reactor avoiding crystal attrition. Different positions and diameter/length ratios are tested to find the optimal hydrodynamic regime for crystal growth. Seeded Constant composition and non-seeded free-drift experiments are conducted under controlled experimental conditions. In the first case, and for calcium carbonate for instance, a metastable supersaturated solution containing Ca2+ and 2- CaCO3 and calcite seeds crystals is kept in motion by means of either mechanical agitation (impeller) or pneumatically. Pneumatic agitation is reached by pumping a N2 and CO2 gas mixture from the bottom of the reactor. Supersaturation is kept constant by maintaining pH constant (between 7.8 and 7.9) injecting the reactants (in this case NaHCO3 and CaCl2) gradually and separately, avoiding supersaturation to occur until the moment of mixing. The feeding CO2 partial pressure is also known at any moment and it is changed according to the pH value as well. The temperature is also controlled and fixed at 298 K by circulating cooling water through the reactor’s outer jacket. The partial pressures of gases in the head space are controlled by adding a CO2/N2 mixture, ensuring there is no CO2 exchange between the solution and the space on top of the reactor. Calcium carbonate crystal growth is then followed avoiding the effect of attrition, off line but also on-line. A closed loop including a flow cell is performed to follow the growth of the crystals by light scattering [1], Atomic force microscopy (AFM) [2,3] high speed imaging [4], infrared spectroscopy or Raman spectroscopy [5]. A new special reactor design offers (hydrodynamic) flexibility and the possibility of avoiding crystal attrition on the study of calcium carbonate crystal growth. By having the possibility of following the crystallization process online and avoiding attrition, it is possible to investigate more in detail the effects of the presence of foreign ions/impurities, and the effectiveness of fresh and recycled antiscalants. References: [1] Ralph. Jonasson, Kevin Rispler, Brian Wiwchar, William D. Gunter, Chemical Geology, 132 (1996) 215- 225. [2] Alexander E. S. van Driessche, Mike Sleutel, Crystal Research and Technology, 1-23 (2013) [3] Manijeh M. Reyhani, Allan Oliveira, Gordon M. Parkinson, Franca Jones, Andrew L. Rohl, Mark I. Ogden, International Journal of Modern Physics B, 16 (2002) 25-33 [4] Sigurd Bauerecker, Peter Ulbig, Victoria Buch, Luboš Vrbka, Pavel Jungwirth, Journal of Physical Chemistry C, 112 (2008) 7631-7636. [5] Jeroen Cornel, Marco Mazzoti, Industrial & Engineering Chemistry Research, 48 (2009) 10740-10745.
S07-P03 Development of in-situ observation svorontystem for high-temperature liquid/solid interfaces: application to solid-source solution growth of AlN
Yoshihiro Kangawa*1, Hideto Miyake2, Michał Boćkowski3, Koichi Kakimoto1
1RIAM, Kyushu University, Fukuoka 816-8580 (Japan) 2Graduate School of Regional Innovation Studies, Mie University, Mie 514-8507 (Japan) 3Institute of High Pressure Physics, PAS, Unipress, 01-142 Warsaw (Poland) *email: [email protected]
Aluminum nitride (AlN) and related compound semiconductors, such as AlGaN, have attracted much attention for use as active layers in deep-UV light-emitting diodes. In order to design AlGaN devices with low dislocation densities, it is indispensable to develop a high quality AlN substrate. In 2011, we have developed an AlN solid-source solution growth (3SG) method which used Li3N as a nitrogen source instead of N2 gas. [1] It was found that growth mode of the material influences on the dislocation propagation and annihilation phenomena. [2] In the present work, we developed an in-situ observation system for high-temperature liquid/solid interfaces, and applied it for 3SG of AlN to understand the initial growth mode. Figure 1 shows a schematic of the experimental apparatus used for in-situ observations of the morphologies of liquid/solid interfaces at high temperatures. We have observed the liquid/solid interfaces through transparent solid materials, i.e., quartz window and AlN/α-Al2O3 substrate. Here, the molar ratio of the source materials was Al:Li3N = 4:1. At high temperatures, Al and Li3N powders melt and form Li-Al-N solution. Figure 2 shows optical images of the Li-Al-N solution/substrate interface. At 23min after the temperature increase (1350°C), we observed the macrostep- Figure 1. Schematic of in- flow growth mode as seen in Fig. 2. Although the grown crystal situ observation system. was polycrystal under the present growth condition, the result suggests that this system could be a powerful tool for investigating inter-facial phenomena at high-temperature liquid/solid interfaces and optimizing crystal growth conditions. Acknowledgements: One of the authors (YK) thank the partial support by a FY2014 Research Exchange Program between Japan Society for the Promotion of Science (JSPS) and Polish Academy of Science (PAS), and KAKENHI Grant Number 25420712. References: [1] Y. Kangawa, R. Toki, T. Yayama, B. M. Epelbaum, K. Kakimoto, Appl. Phys. Express, 4 (2011) 095501. [2] Y. Kangawa, H. Suetsugu, M. Knetzger, E. Meissner, K. Hazu, S. F. Chichibu, T. Kajiwara, S. Tanaka, Y. Iwasaki, K. Kakimoto, Jpn. J. Appl. Phys. (Submitted).
S07-P06 Peculiarities of sapphire nitridation under the influence of the high-energy electron beam Milakhin Denis*1, Malin Timur1, Mansurov Vladimir1, Galitsin Yuri1, Zhuravlev Konstantin1, Bakarov Askhat
1Rzhanov Institute of Semiconductor Physics of the Siberian Branch of the Russian Academy of Science, 630090, Novosibirsk, Russia *email: [email protected]
Nitridation of the sapphire is the most important step in the growth of the III-nitrides on the sapphire. This process involves exposing a substrate to a flow of ammonia at an elevated temperature. Nitridation of the reconstructed surface of the sapphire enriched by aluminum atoms is of special interest, since the presence of metallic bonds on the surface improves the quality of the structure. The nitridation process during ammonia MBE has been studied using reflection high- energy electron diffraction as the reflex of the AlN crystalline phase appears near the reflex of the sapphire. The experimental results were processed in a special program, which measured the intensity of the most informative reflexes. Then, we plotted the dependence of the intensity of appeared reflexes of the AlN crystalline phase on time in the form of kinetic curves. During the processing of the experimental results of nitridation on the reconstructed surface of sapphire it has been found that high-energy electrons have an impact on the process. By heating of the samples by heat radiation from the heater, reconstruction of the surface (1x1) appears. Then the sample is heated to the temperature of 1150 C and the surface of the sapphire (1x1) starts to change to ( 31 31) R9° reconstruction. It is characterized by the sapphire surface depletion of oxygen and aluminum enrichment. However, in our previous work it is shown that there is only a partial recovery of aluminum to the metal state [1]. We have found out that the surface reconstruction of sapphire (1x1) is nitridized for 10 minutes in a 25 sccm ammonia flow, whereas the surface with the reconstruction of ( 31 31 ) R9° is not nitridized and the AlN crystalline phase is not formed. It has been noted that under the influence of fast electrons with the energy of 11 keV, the irradiated section of the ( 31 31 ) R9° reconstructed surface is destroyed within 10 minutes, the surface of the sapphire is restored to its original state with the reconstruction (1x1), and then it is successfully nitridized. To investigate the effect of a high-energy electron beam on the nitridation process, experiments were conducted to destroy the ( 31 31 ) R9° reconstruction to (1x1) at different temperatures (750 °C, 825 °C, 900 °C). The duration of the impact and the intensity of the electron beam varied. The influence of the pulse width depending on the pulse ratio to the kinetics of nitridation of sapphire was studied: in the first case, the momentum of an electron beam was continuous; in the second case the relative pulse duration was S = 2, and in the third one it was S = 20. So we could restore the nitridation kinetics in the absence of exposure to electrons. It has been shown that eliminating the influence of the electron beam the process of forming the AlN crystalline phase goes on appreciably slower and is different from the process in a continuous exposure in k = 6 times. In case of low intensity the nitridation process also slows down. Using the obtained kinetic curves of the nitridation process has made it possible to investigate the influence of the degree of completion of the process of nitridation on the further growth of the AlN buffer layer. This work is supported by RFBR (grant № 13-02-00985).
References: [1] D.S. Milakhin, T.V. Malin, V.G. Mansurov, J.G. Galitsin and K.S. Zhuravlev, Semiconductors, Volume 49, 2015, 925-931.
S07-P07 Using modifiers to mitigate salt crystallization damage in porous building materials: an optical microscopy study of borax and sodium sulfate Granneman Sanne*1, Lubelli Barbara1,2, van Hees Rob1,2,Shahidzadeh Noushine3
1Technical University of Delft, Julianalaan 134, Delft (The Netherlands), [email protected] 2TNO Technical Sciences, Van Mourik Broekmanweg 6, Delft (The Netherlands) 3University of Amsterdam, Institute of Physics, WZI, Science Park 904, Amsterdam (The Netherlands) *email: referring author email
Crystallization of soluble salts in porous building materials is a ubiquitous problem, and a threat to the preservation of our monumental buildings. Lime‐based mortars, commonly used in historic masonry, are especially prone to salt damage due to their low mechanical strength. The deterioration such as scaling and crumbling, is due to the pressure induced by the growing salt crystals from supersaturated solution inside pores [1]. So far, none of the existing solutions to improve the resistance of mortars to salt damage by changing their properties (e.g., using stronger binders or modifying water transport by the use of water‐ repellents) has been completely successful. In recent years, research has been undertaken aiming at influencing the crystallization behaviour by adding modifiers to the mortars instead of modifying the material properties [2]. The modifiers could prevent nucleation (inhibitors), promote nucleation of a certain crystal polymorph (promoters) and/or modify the habit of the crystals (habit modifiers). In this way, salt crystallization can be promoted rather at the surface of the material (efflorescence) than in the pores (crypto‐florescence). This might eventually result in a reduction of the damage. We have investigated the effectiveness of borax (Na2B4O7∙10H2O) as modifier of sodium sulfate, one of the most deleterious salts in buildings. The impact of different borax concentrations on conductivity and wetting properties of sodium sulfate solutions was measured using a Metrohm conductivity probe and the KRUSS apparatus. Furthermore, using direct imaging and optical microscopy [3,4], the nucleation, growth and crystallization pattern of sodium sulfate solutions in the presence of borax were followed in evaporating droplets on glass plates, at controlled temperature and relative humidity. The results were compared with the crystallization dynamics of each of the pure components (i.e., Na2SO4 and borax). Additionally, borax and sodium sulfate were crystallized consecutively (simulation of the situation in a mortar, where borax will already be present when salts enter the material), to observe any differences compared to experiments on mixtures. Our results show that the addition of borax increases the wetting properties of the salt solution (lower contact angle). The improvement of the spreading properties of the solution leads to a higher evaporation rate, which in turn promotes efflorescence. Furthermore, our experiments show how the addition of borax to sodium sulfate leads to changes in crystal morphology in comparison with pure salt solution.
References: [1] Espinosa-Marzal R.M, Scherer G.W., Accounts of chemical research, Advances in understanding damage by salt crystallization. 43 (2010), 897–905 [2] Granneman S.J.C., Ruiz-Agudo E., Lubelli B., van Hees, R.P.J., Rodriguez-Navarro, C., Proceedings of 1st International conference on Ageing of Materials and Structures, Study on effective modifiers for damaging salts in mortar , (2014), 604-611 [3] Shahidzadeh-Bonn N., Rafai S., Bonn D., Wegdam G., Langmuir, Salt crystallization during evaporation: impact of interfacial properties, 24 (2008), 8599-8605 4 Shahidzadeh N, Schut M., Desarnaud J., Prat M., Bonn D., Scientific Reports, Salt stains from evaporating droplets, 5 (2015), 10335.
S07-P08
Optimization of Cooling Crystallization of High Aspect Ratio Crystals in Batch and Continuous Operations for Size and Shape Control
David Acevedoa, Zoltak K. Nagya,*
aSchool of Chemical Engineering, Purdue University, West Lafayette, 47907, IN
The cooling crystallization for potassium dihydrogen phosphate (KDP) was optimized for: (a) batch and (b) continuous process. A two-dimensional population balance model was solved considering secondary nucleation, size independent growth, size independent dissolution and breakage. The breakage model was obtained from literature in which it was assumed that the rate of breakage is proportional to the product of the frequency and energy of the collisions between the crystals and the crystallizer and crystals will become prone to breakage only when their aspect ratio exceeds a certain limit.1 A non-linear optimization problem was solved via sequential quadratic programming in which the aspect ratio or mean size of the length direction was considered as objective function. Previous work the trade-off between the achievable size and shape of crystals for different classes of systems such as KDP while considering primary nucleation and growth.2
The temperature profile was considered as optimization variable for the batch scenario. The optimization results demonstrated that temperature cycling can maximize the growth of both crystal dimensions while minimizing the aspect ratio. Moreover, the continuous process considered is a multi-stage mixed suspension product removal crystallizer and various configurations were considered in order to evaluate the various possible optimal designs while considering the various types of mechanisms. The steady-state temperature at each stage and average working volume were considered as optimization variables for the continuous scenario. The shape and size of KDP were optimized for continuous and batch scenario in which the common trade-off between the objectives was minimized or eliminated by considering multiple mechanisms.
Keywords: Optimization, Shape, Breakage, Continuous crystallization
References: 1. Sato, K.; Nagai, H.; Hasegawa, K.; Tomori, K.; Kramer, H.J.M.; Jansens, P.J. Two‐ dimensional population balance model with breakage of high aspect ratio crystals for batch crystallization. Chemical Engineering Science. 2008, 63:3271‐3278. 2. Acevedo, D. Nagy, Z.K. Systematic classification of unseeded batch crystallization systems for achievable shape and size analysis. Journal of Crystal Growth. 2014, 394:97‐105.
S07-P10 Nanoconfined Crystal Growth investigated by Reflection Interference Contrast Microscopy
Felix Kohler1*, Dag Kristian Dysthe1
1University of Oslo, Sem Sælands vei 24, Oslo (Norway) *email: [email protected] A crystal growing against a surface exerts a force. A good understanding of this growing force is essential to describe the deformation of solids by stresses generated by crystallization. This is particularly relevant for the comprehension of damage by crystallization in porous building materials, which is of great economical importance and fundamental for methods that can help to preserve our cultural heritage [1, 2]. In addition, the fundamental knowledge of these forces is needed for geodynamic modelling that forms a basis for oil exploration and modelling of reservoir compaction. However, the exact behavior of the growth and the dissolution process in close contact to an interface are still not known in detail. The crystallization, the dissolution and the transport of material is mediated by a nanoconfined water film. In contradiction to some theoretical results, which predict a smooth interface, some recent experiments have shown that the nanoconfined growth surfaces are rough. We use methods such as reflective interference contrast microscopy (RICM) for in situ observations of NaClO3 crystals growing against a glass surface (Figure 1). In this study, brittle NaClO3 is used instead of plastically deforming crystals such as halite [3]. In order to carefully control the supersaturation of the fluid close to the crystal interface, we use a temperature regulated microfluidic system (Figure 2). In combination with theoretical studies and Kinetic Monte Carlo simulations we aim at providing more realistic descriptions of surface energies and energy barriers which are able to explain the discrepancies between experiments and the current theory.
Figure 1. Corner of NaClO3 Crystal observed by RICM Figure 2. Control of crystal growth in microfluidic cell. The temperature T2 at the place of the observed crystal is lower than in the rest of the system (T1
References: [1] G. W. Scherer, Cement and Concrete Research, 34 (2004) 1613 [2] Flatt, R. J. , Caruso, F., Sanchez, A. S. A. and Scherer, G. W., Nature Communications, 5 (2014) 4832 [3] Sekine, S., Okamoto, A.,Hayashi, American Mineralogist, 96 (2011) 1012
S07-P12 Microfluidics for in situ study of growth of calcium carbonate
Lei Li1, Dag Kristian Dysthe1*
1University of Oslo, SemSælandsvei 24, Oslo (Norway) *email: [email protected] The controllable synthesis of calcium carbonate (CaCO3) growth has received much attention due to its wide scientific and industrial applications such as paper, rubber, paint, etc. The growth of CaCO3 crystals depends significantly on the composition of the surrounding solution and on the types of surface active molecules. [1] We prepare CaCO3 crystals in a microfluidic cell by precipitation reaction of sodium carbonate with calcium chloride in water. The fluid flow minimizes the effect of convection, diffusion and turbulence due to concentration gradients. This leads to a highly controlled solution concentration around the crystal and allows to study the growth behavior of calcium carbonate with high resolution microscopy methods (Figure 1).For further analysis of the processes that appear in the channel ex situ Raman spectroscopy and scanning electron microscopy have been performed in addition.
A
B
Figure1. (A). Microfluidic network for crystal growth experiments with inlets for different fluids and outlet on right hand. (B). Growth patterns of calcium carbonate for varying supersaturation. Bright field microscopy images performed on Olympus GX71.
References: [1] Anja R., Dag K.D., Journal of Crystal Growth, 346(2012) 89.
S07-P13 In-situ Raman technique applied to monitoring phase transition of linear alkylbenzene sulphonate (LAS)
Boyang. Zou1*, Xiaojun Lai1, Dan Xu2 and Luis Martin de Juan2
1Institute of Particle Science and Engineering, School of Chemical and process Engineering, University of Leeds, Leeds, LS2 9JT, United Kingdom
2 Procter & Gamble, Newcastle Innovation Centre, Newcastle, United Kingdom *email:[email protected] Linear alkylbenzene sulphonate is one of the main components included in powdered washing detergents to help with stain removal. In aqueous solution it usually presents in a mixture of L1 (micelle phase) and La (lamellar phase, liquid crystal) over of wide range of composition, see figure 1. In the process, LAS and other various components are mixed into a slurry, thereafter pumped into a spray drying system. The physical and chemical properties of the spray dried powder are greatly affected by the properties of the slurry; these are essentially derived from the phase behaviours of LAS and the interactions among the different components within the system [1]. Analytical techniques such as SAXS, XRD & DSC are used for LAS phase study. Yet, some of them are either difficult to access or have high operating costs. Others are not suitable for liquid systems or require sample preparation. In this study, In-situ Raman technique is used to measure LAS surfactant with the advantages of requiring no sample preparation, less interference of aqueous media and run-time data output. The effect LAS solution concentration, temperature and ionic strength have on phase composition and transition is considered; these results show agreement with other research in this area [1]. Therefore, it can be concluded that Raman spectroscopy has potential for use in the study of surfactants.
a D - spacing b
Spherical Micelle
Water layer
Cross section Lamellar phase
Figure 1. a: LAS in 3 and 6 positional isomer[1];b: L1 (micelle phase) and La (lamellar phase, liquid crystal) structure References: [1] J. A. Stewart a , A. Saiani, et al., Journal of Dispersion Science and Technology. 2011. 32:12, 1700-1710.
S07-P14 Solubility studies of GaN in NH3/mineralizer-solutions
Thomas G. Steigerwald; Nicolas S.A. Alt; Anna-Carina L. Kimmel; Benjamin Hertweck; Eberhard Schluecker;
Institute of Process Machinery and Systems Engineering, Friedrich-Alexander-University Erlangen- Nuremberg, Erlangen, Deutschland
For the crystallization of binary and multinary nitrides, amides and imides of gallium, aluminum, silicon and germanium, the ammonothermal process is a suitable approach. This solvothermal synthesis uses supercritical ammonia atmosphere at temperatures up to 870 K and pressures of several hundred megapascal to recrystallize nitrides [1]. In the figure a typical autoclave with two temperature regions is shown, one region is the dissolution zone with a feedstock and the other the recrystallization zone with seed crystals. A defined temperature gradient between the two regions is needed, that causes thermal convection in the apparatus. With a baffle the convection can be adjusted specifically. For good crystal quality it is important to recrystallize near the thermodynamic equilibrium, which depends on the solubility of GaN in the ammonia/mineralizer-mixture. The synthesis takes place in thick walled autoclaves, which needs high maintenance for every single experimental run [2]. As research is still in its infancy, for every new precursor/mineralizer combination a lot of gravimetrically analyzed measurements have to be done. In this talk, the solubility curve of the GaN/NH4F/NH3-mixture is shown and reasons for the high time and resource consuming determination are discussed. One result is that solubility depends strongly on temperature. By the use of UV/Vis- spectroscopy it is possibly to estimate a temperature and pressure range where solution of GaN in the mineralizer/ammonia-mixture begins within a single experiment. In a custom-made optical cell the GaN/NH4F/NH3-mixture is analyzed and it could be shown, that some intermediates were formed at 550°C, which leads to a change in the wavelength of the irradiated light. Unfortunately this is only qualitative and not quantitative approach. In polar solvents, like ammonia, the dissolving capacity can be described by the dielectric constant. So as prospect for future research the electrochemical impedance spectroscopy, as it was done by M. Buback et al. for pure ammonia [3], shall be applied to ammonothermal systems to gather solubility data in a fast way. The challenge is a high-pressure, high temperature electrical lead through with low thermal gradients. So some technical drawings of a modified lead through are presented to fulfill these purposes.
[1] Ammonothermal Crystal Growth of GaN Using an NH4F Mineralizer, Q. Bao, et al., Crystal Growth & Design, 2013, 13, 4158-4161 [2] Ammonothermal crystal growth of gallium nitride – A brief discussion of critical issues, D. Ehrentraut, T. Fukuda, Journal of Crystal Growth, 312 (2010) 2514-2518. [3] The Static Dielectric Constant of Ammonia to High Pressures and Temperatures, M. Buback and W. D. Harder, Berichte der Bunsen-Gesellschaft, 1977, 81 (6), 603-614.
S07-P15 Analysis of temperature data obtained by measurements of temperature field at simulated vertical Bridgman crystal growth of PbCl2
Král Robert*1, Nitsch Karel1
1Institute of Physics Czech Academy of Sciences, Cukrovarnicka 10, 162 00 Prague (Czech Republic) *email: [email protected]
Recently, a new method for a direct measurement of the temperature field during simulated crystal growth of lead chloride (PbCl2) by the vertical Bridgman method has been developed [1]. This method allowed detail analysis of heat conditions in the system and determination of the position and the shape of crystal/melt interface. The temperature field presented in this study at first ampoule position, where there was more melt than the crystalline phase in the ampoule, in the steep temperature gradient (35 K/cm) under stationary conditions (zero pulling rate) was measured by four thermocouples. These thermocouples were placed in specially prepared quartz ampoule with four asymmetrically positioned capillaries along the ampoule axis. The temperature field was measured repeatedly four times. Obtained temperature data from all four thermocouples were projected as 2D planar cut under radial symmetry and denoted as isolevels. However, their conversion into isotherms by linear approximation for further analysis was required. Nevertheless, only isotherms 500 °C corresponding to the melting point of PbCl2 lead to identification of the position and shape of crystal/melt interface. Obtained temperature data were analyzed separately and together by calculating an average temperature field. Standard deviation of this average temperature field was evaluated and it was ca. 0.2 K in crystalline phase, 0.4 K in the melt, and 0.2 K in the atmosphere over the melt. Lower values of the standard deviation in the crystal and in the atmosphere points to stable heat flow conditions in these phases than in the melt. On the contrary, the higher standard deviation in the melt could be originated by the heat transport fluctuations caused by changes in the melt buoyancy. Furthermore, first and second derivation of temperature data in dependence on the vertical position in the ampoule measured by each thermocouple were evaluated. The first derivation showed two maxima in vertical position at around 7 and 49 mm, which were in agreement with both the vertical position of crystal/melt interface and melt surface captured, when the ampoule was pulled out from the furnace during simulated crystal growth. Moreover, the shape of the crystal/melt interface was determined by fitting the isotherms 500 °C with a circle function using a least square method. The position of the circle center as well as its radius were the key parameters determining if the shapes of the isotherm 500 °C were convex into the melt, concave, or planar ones. This contribution deals with a statistical evaluation of measured temperature data and continues in our previously presented work [1]. The goal of this work is to find suitable growth conditions for preparation of high quality single crystals of lead halides and ternary alkali lead halides considered to be suitable as hosts for mid-IR lasers [2].
Acknowledgment: This work was supported by the Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for Exploratory Research (AY) for JSPS Postdoctoral Fellowship for Foreign Researchers (P14040) and Czech project MEYS KONTAKT II, no. LH14266.
References: [1] R. Král, J. Cryst. Growth 360 (2010) 162–166. [2] R. Král, K. Nitsch, V. Babin, J. Šulc, H. Jelínková, Y. Yokota, A. Yoshikawa, M. Nikl, Opt. Mater. 36 (2013) 214–220.
S07-P16 Controlling Ice Growth Using Selective Infrared Radiation
Guy Shlomit*, Yashunsky Victor, Chayet Haim and Braslavsky Ido
Institute of Biochemistry, Food Science and Nutrition, Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel. *[email protected]
Freezing is used to preserve cells, tissues and food for a long period of time. However, ice formation during the preservation procedure can be destructive. For example, ice recrystallization is an Ostwald ripening process, in which larger ice crystals grow on the expense of the smaller ones. This process causes damages to food and biological systems, as a result of mechanical disruptions by the growing ice crystals during freezing and thawing. To achieve a successful cryopreservation, the formation of growing ice crystals must be controlled. This research examines the implication of selective infrared (IR) radiation on ice and partially frozen systems. We propose to control and manipulate ice growth using selective IR radiation, which is absorbed by the ice more efficiently than by water. Using the selective radiation, we have found a unique ice pattern, in the shape of holes and micro-channels. Pattern formation is found in nature in many scenarios, for example: desert vegetation and skin color of animals, such as fish and zebras. Those patterns resulted from processes of reaction-diffusion. We intend to use a reaction-diffusion model to explain the special ice pattern that was observed in our system. The model will include the heat that is created by the radiation and diffuses according to the temperature gradient. The temperature determines the phase, which is also time dependent. Based on these findings, we propose to combine ice binding materials, as they are used as a known method to control ice growth. Antifreeze proteins and the synthetic material Zirconium Acetate, by binding to an ice crystal, inhibit ice growth and depress ice recrystallization. They possess ice shaping properties as well. We will investigate the selective radiation in combination with ice binding materials as a method to control ice shaping, ice growth and recrystallization. The ice growth modifications can be used to improve cryopreservation procedures.
Acknowledgements: European Research Council (ERC) Israel Science Foundation (ISF)
S07-P17 Electron Microscopy Studies of Growth and Structure of MoS2-based Hydrodesulfurization Catalysts
Lars P. Hansen1, Erik Johnson2, Quentin M. Ramasse3, Christian Kisielowski4, Michael Brorson1 and Stig Helveg*1 1. Haldor Topsøe A/S, Nymøllevej 55, DK-2800 Kgs. Lyngby, Denmark. 2. Nano-Science Center, Niels Bohr Institute, Universitetsparken 5, DK-2100, Copenhagen, Denmark. 3. SuperSTEM Laboratory, STFC Daresbury, Keckwick Lane, Daresbury WA4 4AD, United Kingdom 4. Lawrence Berkeley National Laboratory, National Center for Electron Microscopy and Joint Center for Artificial Photosynthesis, Berkeley CA 94708, United States of America. *email: [email protected]
Production of transport fuels with ultra-low sulfur contents in oil refineries requires very efficient catalytic hydrodesulfurization processes. As new environmental legislation for clean fuels demands an enhanced removal of sulfur and other impurities from mineral oil, attention is currently being devoted to understand the catalysts’ structure-activity relationships. In oil refineries, the hydrodesulfurization catalysts are based on highly anisotropic MoS2 nanocrystals as the active component [1,2]. It is well-known that the catalytic reactivity of the MoS2 nanocrystals is associated with their exposed edges, size and morphology. However, although MoS2-based catalysts are synthesized at a very large scale in the refining industry, insight into the structure and dynamics of the MoS2 nanostructures has remained a challenge to unveil. Recent advancements have made (scanning) transmission electron microscopy (S/TEM) a powerful technique for studying individual (supported) nanoparticles at the atomic-level [3-5]. In this presentation, we demonstrate the application of such advancements for single atom sensitivity and in situ electron microscopy of MoS2-based hydrotreating catalysts. By means of time-resolved TEM imaging, the growth of MoS2 nanocrystals is monitored in situ during the sulfidation reaction that transforms a molybdenum oxide precursor material into highly dispersed MoS2 nanocrystals (Figure 1). Specifically, the time-resolved image series provide new information about the evolution of MoS2 nanocrystals with different size, morphology and stacking and thus uncover the nucleation and growth of the MoS2 nanocrystals. The in situ observations are beneficially combined with single-atom sensitive imaging by S/TEM, and thus provide unprecedented new insight into the formation of MoS2 nanocrystals with specific distribution of active sites.
Figure 1. (a) In situ sulfidation of molybdenum oxide precursor dispersed on a Mg-spinel support during exposure to 1 mbar H2S:H2 1:9 at 690 ºC. (b) High resolution STEM image of a region at the catalytically important edge of a MoS2 nanoparticle in (001) projection on a graphite support. [4,5].
References: [1] H. Topsøe et al, Hydrotreating Catalysis, vol. 11, Springer, Berlin (1996). [2] F. Besenbacher et al, Catal. Today, 130 (2008), p. 86. [3] C. Kisielowski et al, Angew. Chem., Int. Ed. 49 (2010), p. 2708. [4] L. P. Hansen et al, Angew. Chem., Int. Ed. 50 (2011), p. 1015 [5] L. P. Hansen et al., J. Phys. Chem. C 118 (2014), p. 22768
SESSION 8
Epitaxial Growth - Crystal Growth Interfaces
Analysis of critical thickness for generated misfit dislocation in GaInN/GaN superlattice on GaN by in situ X-ray diffraction Junya Ohsumi*1, Koji Ishihara1, Taiji Yamamoto1, Motoaki Iwaya1, Tetsuya Takeuchi1, Satoshi Kamiyama1, and Isamu Akasaki1,2 1Faculty of Science and Technology, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468-8502, Japan 2Akasaki Research Center, Furocho, Chikusa-ku, Nagoya University, Nagoya 464-8603, Japan *email: [email protected] The GaInN/GaN superlattice (SL) structure is used as the active layer in commercially available visible-light emitting devices. There are many interesting features that make these nitride semiconductor alloys especially useful for efficient light emitters. In addition, these materials are also useful as a high conversion efficiency solar cell. Most devices using GaInN/GaN SL are fabricated on GaN, because the growth of thick GaInN films with high crystallinity on substrates other than GaN is very difficult. Several studies have been previously conducted to elucidate the mechanism by which defects form via strain relaxation in GaInN/GaN SL structures, because it is necessary to minimize defect formation in order to improve device performance. However, current understanding of the critical layer thickness at which misfit dislocations are introduced in GaInN/GaN SL structures is insufficient. In this study, we observed the growth of the GaInN/GaN SL structure by in situ X-ray diffraction monitoring. The samples were grown on c-plane sapphire substrates using metalorganic vapor phase epitaxy apparatus with a horizontal face down 2” × 3” reactor. After the growth of a 3-μm-thick GaN template at 1,050 °C on c-plane sapphire covered with a
3 low-temperature GaN buffer layer using H2 carrier gas at 10 933 hPa, it was cooled to 750 °C and the carrier gas was changed to N2. Then, GaInN/GaN SL structure was grown 2 on the GaN template. The threading dislocation density of 10 the GaN template was ~3 × 108 cm-2. We evaluated the 1 GaInN films with symmetric (0002) Bragg diffraction using 10 an in situ XRD system. As the results, the satellite peaks Single layer
Thickness (nm) Thickness SL (only GaInN thickness)
0 from the -1st to the +1st order can be obtained from these in 10 situ X-ray diffraction spectrums. From the full width at half 0.0 0.1 0.2 0.3 maximums (FWHMs) of the 0th and -1st satellite peaks as a InN molar fraction function of the SL periods, we observed a clear trend in each Figure 1. Critical thickness of the FWHM. It was found that by analyzing this trend along with total GaInN thickness in florescence microscopic and transmission electron GaInN/GaN SL and single GaInN microscopic analysis, an analysis of the In segregation and layer as function of InN molar misfit dislocation are possible. Accordingly, if we employ in situ X-ray diffraction under various growth conditions, the optimization of the growth conditions will become easier because it would be possible to determine the number of periods at which In segregation and misfit dislocation increases by only one growth procedure. We also investigated the thickness of this saturated FWHMs for various InN molar fractions from the behavior of the FWHMs by in situ XRD measurements, as shown in Fig. 1. We also compared our experimental results of single GaInN samples. From this figure, critical thickness of GaInN and GaInN SL was almost same. In addition, we will discuss relaxation and surface state by AFM, SEM, and XRD mapping. Acknowledgement This study was partially supported by the Program for the Strategic Research Foundation at Private Universities, 2012–2016, supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) , a MEXT Grant-in-Aid for Specially Promoted Research #25000011, and the MEXT Grant- in-Aid for Scientific Research A #15H02019.
In situ observation of low temperature growth of Ge on Si(111) via RHEED
Andreas Grimm*1, 2, Andreas Fissel1, Eberhard Bugiel1, H. Jörg Osten1, 2,3, and Tobias F. Wietler1 ,2 ,3
1 Institute of Electronic Materials and Devices, Schneiderberg 32, D-30167 Hannover, Germany 2 Hannover School for Nanotechnology, Schneiderberg 39, D-30167 Hannover, Germany 3 Laboratory of Nano and Quantum Engineering, Schneiderberg 39, D-30167 Hannover, Germany *email: [email protected]
The integration of Ge into existing silicon-based technology is the key approach to new functionality extension of Moore´s Law. Ge provides the potential to combine photon based data processing with Si complementary metal oxide semiconductor processing (CMOS). Epitaxial Ge films enable a monolithic integration of optoelectronic devices into silicon-based technology. Ge used as buffer system, is a candidate for III-V integration on Si. Having strong light absorption in near-infrared wavelength range as well as a pseudo-direct band gap behaviour [1] Ge-based Laser systems or Ge photodetectors can be achieved [2,3]. The pseudo-direct band gap behaviour is only observed in tensile strained Ge films, which makes precise control of growth parameters and strain engineering necessary. Growth processes in MBE can be analysed and controlled using reflection high energy electron diffraction (RHEED). RHEED is the most widespread method for in situ analysis of thin film surface structure and provides an opportunity for real time observation of epitaxial growth. The initial stages of Stranski-Krastanov growth mode of Ge on Si(111) were investigated by Ichikawa and Ino [4] for a wide range of temperatures (from RT on with subsequent heating). Deelman et al. added in situ strain relaxation studies of Ge epitaxy on Si(111) for temperatures from 450 °C up to 700 °C [5,6]. Here, we investigate Ge epitaxy on Si(111) using RHEED in a growth temperature regime of 200 °C to 400 °C with growth rates ≈ 1 ML/min. The different stages of Stranski-Krastanov growth mode, i.e. wetting layer formation and subsequent islanding, are identified via spot intensity analysis [7]. With increasing Ge layer thickness strain is accumulated due to the lattice mismatch of 4.2% to Si. At a certain critical thickness dc, the film minimizes its total energy via elastic and plastic relaxation. Elastic relaxation proceeds via island formation whereas plastic relaxation is obtained by introduction of misfit dislocations. Hence, we obtained information about the critical layer thickness at low temperatures. The critical thickness dc for the inset of elastic/plastic relaxation is determined by spot intensity analysis to 3.1 < dc < 3.4 ML and is in good agreement with thermodynamic considerations. Additionally, RHEED provides in situ access to the degree of strain relaxation. The strain relaxation process is qualitatively made visible and corroborates spot intensity analysis (inset of relaxation around 3 ML ± 0.5 ML). The relaxation of grown Ge islands is verified by ex situ Transmission Electron Microscopy (TEM) investigations, which show partially relaxed Ge islands. An ordered dislocation network is already visible at growth temperatures of 200 ˚C.
References: [1] C. van de Walle, Phys. Rev. B 39 (1989) 1871. [2] S. Wirths, R. Geiger, von den Driesch, N., G. Mussler, T. Stoica, S. Mantl, Z. Ikonic, M. Luysberg, S. Chiussi, J. M. Hartmann, H. Sigg, J. Faist, D. Buca and D. Grützmacher, Nature Photon 9 (2015) 88. [3] J. Liu, R. Camacho-Aguilera, J. T. Bessette, X. Sun, X. Wang, Y. Cai, L. C. Kimerling and J. Michel, Thin Solid Films 520 (2012) 3354. [4] T. Ichikawa and S. Ino, Surface Science 136 (1984) 267. [5] P. W. Deelman, T. Thundat and L. J. Schowalter, Applied Surface Science 104-105 (1996) 510. [6] P. W. Deelman, J. Vac. Sci. Technol. A 15 (1997) 930. [7] K. Miki, K. Sakamoto and T. Sakamoto, MRS Proc. 148 (1989) 323.
Structural and electrical characteristics of AlGaN/GaN heterostuctures with thin AlN interlayer on sapphire substrate grown by MOCVD
Raju Ramesh*1, 1Kandasamy prabakaran 1 ,Ravi Loganathan1, 2Manavaimaran Balaji2, Eric Faulques3, Alexandre CRISCI4,Krishnan Baskar1
1Anna University,Crystal Growth Centre, Chennai,India 2Madras University, Centre for Nanoscience, Chennai, India 3AffInstitut des Matériaux Jean Rouxel, Université de Nantes,France 4Ingénieur d'études, CNRS, Laboratoire SIMaP,France *email: [email protected]
Thin AlN interlayers are widely used in (Al,Ga)N based high-electron-mobility transistors (HEMT) to improve the mobility of the two-dimensional electron gas forming at the GaN/(Al,Ga)N interface.[1,2]. AlGaN/GaN heterostructure with thin AlN inter layers (IL) of 1 to 3 nm thickness were grown on 2”c-plane sapphire substrates by metalorganic chemical vapour deposition. The structural, optical and electrical quality of epilayers have been characterized by high-resolution X-ray diffractometer (HRXRD), atomic force microscopy (AFM), photoluminescence spectra (PL), Raman scattering spectrometer and Hall measurement. The AlN- IL is believed to have a direct influence to improve the quality of the AlGaN epilayer. Upon optimizing AlN-ILthickness at 3 nm a high crystalline quality with a full width at half maxima (FWHM) for the (0002) and (10-12) planes of GaN as 373 and 672 arc-sec, respectively has been achieved. The AlGaN epilayer also revealed atomic level step with a root mean square (RMS) roughness of 0.16 nm (figure. 1a). In Raman spectra, the mode at 748 cm-1is attributed to the A1(LO) mode of AlGaN and AlN-IL effects. The 2DEG concentration has been found decrease 13 -2 12 -2 from 1.2 x10 cm to 9.8 x10 cm on increasing the AlN-IL thickness. On the other hand, the mobility of 2DEG was found to be increased (figure 1.b) The structural and electrical properties of AlGaN/GaN HEMTs with AlN-IL were characterized and the results have been discussed in detailed.
a b
Figure 1.(a) AFM images on the surface of AlGaN/GaN with 0-3 nm AlN interlayer (b)Hall mobility from 80K to 350 K
References: [1] Haoran Li., Stacia Keller., Silvia H Chan., Jing Lu., Steven P DenBaars and Umesh K Mishra Semicond. Sci. Technol., vol. 30 (2015), PP.055015 (7pp). [2] Tülek, R, Ilgaz, A, Gökden, A, Teke, A, Öztürk, M. K, Kasap, M & Özbay, E 2009, Journal of Applied Physics, vol. 105, no. 1, pp. 013707.
Two-dimensional Si/Si(111)-(7×7) nucleation affected by step permeability and sink to atomic steps
Rogilo Dmitry*1,2, Fedina Liudmila1,2, Kosolobov Sergey1,2, Ranguelov Bogdan3, Latyshev Alexander1,2
1Institute of Semiconductor Physics, pr. Lavrentieva 13, Novosibirsk (Russia) 2Novosibirsk State University, Pirogova Str. 2, Novosibirsk (Russia) 3Institute of Physical Chemistry, Bonchev Str. 11, Sofia (Bulgaria) *email: [email protected]
The two-dimensional nucleation and growth (2DNG) of Si is studied by in situ ultrahigh vacuum reflection electron microscopy (UHV REM) on the step-bunched Si(111)-(7×7) surface
( 10 μm wide terraces) and on extra-large (~100 μm) step-free terraces at 600–750°C. In both cases, the epitaxy starts with classical 2DNG. However, after Θ~100 ML Si deposition we observed the formation of pyramid-like waves in the former case (Fig. 1a) and many separate triangular pyramids in the latter case (Fig. 1b). We used the 2DNG on the step-bunched surface to obtain the dependences of both 2D island concentration N2D and critical top layer width λ on sample temperature T, deposition rate R, and initial terrace width. From the analysis of λ2(T,R) scaling we have detected at T≈720°C the transition from the diffusion limited growth kinetics to the kinetics limited by 0.9 eV barrier for the preferential attachment to descending steps [1]. We attribute this barrier to the impeded double kink nucleation at -type faceted step edges that provides the triangular faceting and the 2 permeability of steps. When comparing the λ (R) and the N2D(R) dependences, we first show that the kinetically limited sink of adatoms to descending permeable steps causes downhill adatom current and the increase of critical nucleus size i by up to 10 times at the top layer of the pyramid- like waves. In contrast to the step-bunched surface, Si deposition (Θ≈300 ML) onto the extra-large step-free terraces leads to the formation of many separate triangular pyramids (Fig. 1b). Based on the linear slope of pyramids’ layer coverage distribution (Fig. 1c), we conclude that the formation of pyramids at the step free surface is caused by the destabilizing net uphill adatom current triggered by -type island edge permeability in accordance with modern theoretical conceptions [2, 3].
The work is partially supported by projects of RFBR (No. 14-02-31440), MESRF (No. 14.621.21.0004), and RSF (No. 14-22-00143).
Figure 1. Si(111)-(7×7) surface morphology after prolonged Si deposition: (a) a pyramid-like wave formed on the step-bunched surface, (b) triangular pyramids formed on an extra-large step-free surface, and (c) its layer coverage distribution
References: [1] Rogilo D., Fedina L., Kosolobov S., Ranguelov B., Latyshev A., Phys. Rev. Lett., 111 (2013) 036105 [2] Hervieu Yu., Markov I., Surf. Sci., 628 (2014) 76 [3] Korutcheva E., Koroutchev K., Markov I., Eur. Phys. J. B, 86 (2013) 60
Epitaxial growth of Ge/Si nanostructures on Si surface patterned by ion irradiation
Zh.V. Smagina*1, A.V. Zinovyev1, N.P. Stepina1, A.F. Zinovieva1, S.A. Rudin1, P.L. Novikov1,2, V.A. Seleznev1, A.V.°Dvurechenskii1,2
1Institute of Semiconductor Physics SB RAS, Lavrentjeva 13, Novosibirsk, 630090 (Russia) 2Novosibirsk State University, Pirogova 2, Novosibirsk, 630090 (Russia) *email: [email protected]
Self-assembled Ge quantum dots (QD) on Si(100) have been intensively investigated as the basis of novel electronic and optical devices. The space-ordered arrays of Ge QDs with little dispersion of size are generally required for any practical applications. Many research groups work at the development of methods of ordered structures fabrication. In this work we have proposed a method of Ge QDs growth on prepatterned Si substrates obtained by a combination of nanoimprint lithography and ion irradiation. The original idea of the selective etching of irradiated Si domains was used to create the periodically stripped structure (80 nm-wide trenches, 100 nm-wide interspacing (ridges) on Si with relief height varyied from 10 to 80 nm. The shape and depth of the relief was controlled by the proper choice of ion dose and energy as well as by the number of etching steps [1]. It was found that during the heteroepitaxy of Ge on a prepatterned Si(100) surface the Ge nanoislands are arranged as linear chains on the ridges, if the trench depth is in the range of 15-30 nm, which is smaller than the projected ion range. The nanoislands grow inside trenches in the case of deep etching, during which radiation defects are removed almost completely. The island density and size strongly depend on the substrate temperature and deposition rate during epitaxy. The optimal temperature and deposition rate at which we obtain most homogeneous nanoislands arrays are 600°С and 0.1 ML/c, respectively. This method was used to create multilayer nanocluster structures, representing three-dimensional crystals of quantum dots in a crystalline matrix. Chemical content, structure and electronic properties of the grown structures were studied by Raman scattering, high resolution electron microscopy and photoluminescence (PL). Intensity of PL of structures with space-arranged islands was found to be three times greater than that in the case of randomly located islands. Transport measurements were carried out for the current lines oriented along or perpendicular to the dot chains. Strong anisotropy of the conductance was observed indicating one-dimensional (1D) character of electron transport. At low bias voltages the charge transport is described by Arrhenius law typical for 1D conductance and is determined by crucial role of highly resistive segments on the conducting paths. An evidence of line ordering of QDs was obtained from electron spin resonance (ESR) spectra. Recently it was found that the ESR line width is broadened with deviation of magnetic field from the growth direction for structures with non- ordered QDs [2]. This case is typical for Dyakonov-Perel spin relaxation, which is due to the random walk of electrons in the plane. In the case with ordering of dots along lines the directions of electron hops are not random, therefore we don’t observe the broadening of the ESR line width. The microscopic mechanism of atom diffusion on a prepatterned surface and growth of Ge/Si structures were studied by molecular dynamics and Monte Carlo simulations. The analysis has shown that introduction of ion-irradiation-induced interstitial atoms leads to the suppression of island nucleation inside trenches. The work was supported by RFBR (Grant 13-02-01181, 13-02-00901).
References: [1] Smagina Zh.V., Stepina N.P., Zinovyev V.A. et al., APL, v. 105 (2014), p. 153106. [2] Zinovieva A.F., Dvurechenskii A.V., Stepina N.P. et al., Phys. Rev. B, v. 77 (2008), p. 115319.
Self-assembled strained GeSi nanoscale structures grown by MBE on Si(100)
Alexandr Nikiforov1, 2, Vyacheslav Timofeev1, Artur Tuktamyshev1, Michail Esin1, Serge Teys1, Oleg Pchelyakov1, 2
1A.V. Rzhanov Institute of Semiconductor Physics SB RAS, Lavrentjeva 13, 630090 Novosibirsk, Russia 2National Research Tomsk State University, Lenin Prospect 36, 634050 Tomsk, Russia
Nanostructures are particularly important objects in the nano - and optoelectronics. The basic materials investigations have focused on the modification of the material to improve its optical and electronic properties in order to realize the efficient light emitting or absorption [1]. The experiments have been carried out by a molecular beam epitaxy (MBE) installation “Katun”. Ex situ scanning tunnel microscopy (STM) with an ultrahigh vacuum instrument “Omicron-Riber” was used for the observation of the surface morphology. The difference in surface energy for the strained planes of Ge(100) and Ge(105) is sufficiently small, hence the islands with {105} facet (hut-islands) are energetically more favorable in the low- temperature range as compared with the dome-islands which contain the facets with the surface energies significantly greater than the strained face of Ge(100). On the other hand, dome-islands are energetically more stable than the hut-islands due to the greater degree of the strain relaxation. At high temperatures, the value of the anisotropy becomes smaller due to the increase of the entropy and thereby the barrier lowers to the formation of dome-islands. By forming of the thin Ge wetting layer and the subsequent annealing process we have obtained nanowires which were observed at the annealing temperature of 450°C. In the beginning the Ge film grows at the temperature of 500°C then the temperature of the substrate is reduced and this layer is annealed for 10 hours (figure 1). The Ge thickness corresponds to the wetting layer with the accumulated elastic strains. The surface morphology of the Ge layer have been demonstrated in figure 4. We have carried out our experiments in the wide range of annealing temperatures of 300- 650°C. The same structures containing nanowires were obtained by Zhang et al. [2]. The work is supported by the RFBR ( Projects 14-29-07153) and by The Tomsk State University Academician D.I. Mendeleev Foundation Program (Research grant No 8.2.10.2015).
Figure 1. STM image (400x400 nm) of Ge film after 10 h annealing at 450oC.
References: [1] A.I. Yakimov, A.I. Nikiforov, V.A. Timofeev et al., Semicond. Sci. Technol. 26, 085018 (2011). [2] J.J. Zhang, A. Rastelli, O.G. Schmidt et al., Appl. Phys. Lett., 103, 083109 (2013).
Quantum dot chains in InAs/GaAs multistacked structures grown by MBE: a strain analysis by FEM Latini Valerio*,1, Placidi Ernesto1,2, Arciprete Fabrizio1, Magri Rita3, Patella Fulvia1
1Dipartimento di Fisica, Università di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133, Roma (Italy) 2CNR - Istituto di Struttura della Materia, Via del Fosso del Cavaliere 100, 00133 Roma (Italy) 3Dipartimento di Fisica, Università degli Studi di Modena e Reggio Emilia and Centro S3 CNR - Istituto di Nanoscienze, Via Campi 213/A, 41100 Modena (Italy) *email: [email protected]
A great interest in controlling the positions of Quantum Dots (QDs) over substrates has widely arisen over the last decades, because of its potential in the fields of quantum information and sophisticated optoelectronic devices [1]. Advances in the fabrication of ordered QD arrays have been obtained by combining bottom-up and top-down methods before and/or after the epitaxial growth. The bottom-up methods allow reaching higher crystalline quality and reducing the cost of processing; on the other hand they require the capability of closely tailoring the growth processes. Three-dimensional stacking of self-assembled QDs in multilayer structures provides an efficient tool to control both the vertical and lateral arrangement of QDs in several systems. In the case of InAs/GaAs we have shown [2] an innovative way to induce the self-assembling of chains of InAs QDs parallel to the direction over mounded GaAs surfaces, even from the first QD layer. In this work, we grew multilayer InAs/GaAs samples in a Molecular Beam Epitaxy (MBE) chamber under critical growth conditions [2] and we observed the occurrence of distanced sets of ordered n-fold parallel chains of QDs along the direction over mounded surfaces [3]. We measured the in-line distances along the QD chains to study the correlation among them. The shape of the in-line distance distributions suggested a progressive ordering of the QD positions with average distance of about 75 nm, as the number of layers was increased. In order to deepen our understanding of the QD arrangement, a sequence of several stacked layers was modelled to simulate an experimental InAs/GaAs(001) multilayer. The COMSOL Multiphysics package was used as a Finite Element Method (FEM) solver for the stress–strain equations of the elasticity theory and to predicting the favourable locations where the InAs QDs of the next layer are positioned [4]. The standard deviation relative to the average distance was assumed as the reference parameter to evaluate the in-line ordering of QDs. The simulated data showed a decreasing behaviour of the that is similar to the experimental trend, confirming a tendency to the in-line ordering of the QDs as a function of the number of layers. On the other hand, further FEM simulations revealed that the strain driving force seems to be insufficient to reduce the QD displacement from the line. We concluded that the strain field of the buried QDs plays a crucial role in rendering the in-line distances between the QDs uniform, whereas the alignment of the single QD chain is mainly related to the morphological features of the rippled surface.
References: [1] Petroff P. M., Advanced Materials, 23 (2011) 2372 [2] Arciprete F., Placidi E., Magri R., Fanfoni M., Balzarotti A., Patella F., ACS Nano, 7 (2013) 3868 [3] Placidi E., Arciprete F., Latini V., Latini S., Magri R., Scuderi M., Nicotra G., Patella F., Applied Physics Letters, 105 (2014) 111905 [4] Latini V., Placidi E., Arciprete F., Patella F., Journal of Crystal Growth, 419 (2015) 138
A study of -Ga2O3 hetero-epitaxial layers grown by MOCVD and ALD
F. Boschi 1, M. Bosi2, E. Buffagni2, T. Berzina2, C. Ferrari2, R. Fornari 1
1Dept. of Physics and Earth Sciences, Univ. of Parma, Area delle Scienze 7/A, 43124 Parma (Italy) 2CNR-IMEM Institute, Area delle Scienze 37/A, 43124 Parma (Italy)
In the past few years semiconducting sesquioxides, and especially -Ga2O3, attracted renewed attention as large single crystals and high-quality homo- and hetero-epitaxial layers became available, which resulted in novel electronic devices. Motivated by these exciting developments, we recently started an activity on deposition and study of Ga2O3 on c-oriented sapphire. To this purpose, we refurbished an MOVPE reactor in order to allow the use of water as oxidizing agent. The reactor can be used either for standard MOCVD process or for atomic layer deposition (ALD) by alternating the oxygen and gallium supply. The principal advantage of ALD consists in enabling the growth of high-quality films at lower temperature. When using MOCVD, the morphology and structural perfection of the hetero-epitaxial films was seen to strongly depend on deposition temperature and partial pressure of the reagents. Up to 550 °C the layers were smooth and featureless but practically amorphous, whilst films grown at temperatures of 650 °C were again smooth (see Fig. 1, Atomic Force Microscopy image, also confirmed by SEM) but exhibited very distinct X-ray peaks, which were unambiguously ascribed to -Ga2O3. X-ray measurements confirmed that the Ga2O3 films are (-201) oriented as previously reported, which means that (-201) planes of the monoclinic structure lie parallel to the basal plane of the hexagonal sapphire substrate. Often the rocking curves showed that the diffraction peaks were shifted with respect to the expected angles. In a sample grown at 715 °C the peaks actually occupied their nominal positions but were broader. At present, we do not have a univocal interpretation of this feature, even if strain and defects, and possibly film stoichiometry, are certainly involved. On the other hand, the ALD layers appeared to be single crystalline and exhibited good X-ray diffraction profiles already at deposition temperature of 550 °C, although the peak shift observed in MOCVD epilayers was still present. In this paper, we shall present our experimental results and compare the main properties of - Ga2O3 epilayers prepared by ALD and MOCVD.
Figure 1: AFM picture of the surface of Ga2O3 film deposited at 650 °C, thickness 300 nm; the scan on the right hand side shows that the roughness is ± 2nm.
Step density waves on vicinal crystal surfaces
Bogdan Ranguelov, Stoyan Stoyanov
Institute of Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria) *email: [email protected]
We present a new idea of an instability of a vicinal crystal surface at growth or evaporation with fast moving steps. Our treatment is going beyond the quasi-static approximation used in the classical crystal growth model of Burton, Cabrera and Frank, where the basic assumption is that the steps move slowly. In contrast, we study crystal growth and evaporation phenomena in the case of very fast surface diffusion of adatoms and taking into account the time dependence of the adatom concentrations on terraces with different sizes. The new type of instability forms a traveling step density waves on the vicinal crystal surface and it is presented when the step velocity exceeds a specific critical value, related to the strength of the repulsion between individual steps (a possible situation in MBE growth experiments). This instability is caused solely by the high velocity of the step motion in contrast to the step bunching instability, where the surface is destabilized by surface adatom electromigration, impurities or Erlich-Schwoebel effect.
Figure 1. Model view of the vicinal crystal surface with straight steps – evaporation, step kinetic coefficient, electromigration force and step permeability Our model is extended by taking into account the electromigration effect (F) and step permeability (P) both in the cases of growth or evaporation of the vicinal crystal surface (Figure 1). We show that the interplay between step velocity, electromigration and step permeability produces a variety of spatial and temporal surface instability patterns. The presentation is accompanied by an unique real time reflection electron microscopy movies of surface instabilities on Si(111) at different temperatures and growth regimes.
References: [1] Ranguelov B., Stoyanov S., Phys. Rev. B 76, 035443 (2007) [2] Ranguelov B., Markov I., Cent. Eur. J. Phys. 7 (2), (2009), 350 – 355 [3] Chernov A. A., J. Crystal Growth 264 (2004), 499
Structural study of the innovative 3C-SiC/Si/3C-SiC/Si heterostructure for electro-mechanical applications
R. Khazaka1,2, J.F. Michaud1, P. Vennéguès2, D. Alquier1 and M. Portail2
1 Université François Rabelais, Tours, GREMAN, CNRS-UMR 7347, 16 rue Pierre et Marie Curie, BP 7155, 37071 Tours Cedex 2, France 2 CRHEA, CNRS-UPR10, rue Bernard Gregory, 06560 Valbonne, France *email: [email protected]
The cubic silicon carbide (3C-SiC) is an interesting wide band gap material with outstanding properties, very promising for designing Micro-Electro-Mechanical Systems (MEMS) devices operating in harsh environment where Si-based devices reveal a shortage in their performance. Furthermore, 3C-SiC can be heteroepitaxially grown on low-cost substrates, as silicon. This is of interest for taking benefit from the SiC properties conserving a reduced development cost. Of course, the successful development of a 3C-SiC/Si based sensor family is largely conditioned to a good management of two major issues related to the large lattice mismatch as well as the large thermal coefficient expansion mismatch between Si and SiC which make the growth of SiC on Si and the reverse, i.e. Si on SiC, a real concern. That is a reason why if the prime growth of 3C-SiC on Si substrates is well documented, the further growth of stacked 3C-SiC/Si structures on a Si substrates, of high potential for designing original resonant structures, is, by far, less discussed. In this presentation, we will give at first a general overview on this topic as well as on the potential applications that this heterostructure can offer. In a second time, we will present an extended structural investigation of a complete 3C-SiC/Si/3C-SiC heterostructure grown on a Si(001) substrate by means of chemical vapor deposition (CVD). We will underline the specific growth mode of each level of the structure. Indeed, starting from a [001] oriented 3C-SiC epilayer, we observe a successive rotation of the growth direction. The Si epilayer is grown along the [110] direction while the top 3C-SiC layer is grown along the [111] axis. This switch in growth direction is interesting from fundamental as well as applications point of view since the material properties is directly linked to the orientation. The inclusion of hexagonal silicon is also observed in this structure. Finally, the antiphase domains in the first 3C-SiC layer has been proved to be responsible on the domains formation in silicon epilayer [1]. These domains in the Si epilayer induces the rotation of the domains in the subsequent 3C-SiC epilayer. All these points will be discussed both from a fundamental point of view and within a more practical point of view of their interest for MEMS applications.
Figure 1. Cross-section TEM image of the 3C-SiC/Si/3C-SiC/Si heterostructure and high resolution TEM images for the Si(110)/3C-SiC(001) and 3C-SiC(111)/Si(110) interfaces.
References: [1] R. Khazaka, M. Portail, P. Vennéguès, D. Alquier, J.-F. Michaud, Acta Materialia (2015) (submitted).
Functionalization of SiC Nanowires by Supersonic Molecular Beams for Photodynamic Therapy Tatti Roberta*1, Aversa Lucrezia1, Verucchi Roberto1, Fabbri Filippo2, Rossi Francesca2, Attolini Giovanni2, Bosi Matteo2, Salviati Giancarlo2 and Iannotta Salvatore2
1IMEM-CNR Institute, Via alla Cascata 56/C, Povo (Italy) 2IMEM-CNR Institute, Parco Area delle Scienze 37/A, Parma (Italy) *email: [email protected]
Photodynamic Therapy (PDT) is a therapeutical approach in the cancer treatment, which consists in the activation of a photosensitizer (phorphyrins) with visible light in order to produce singlet oxygen, to exert a cytotoxic activity towards cancer cells. The use of visible light limits the PDT application only to shallow deseases, for this reason we propose a new “X-Ray induced PDT” approach, using nanohybrid systems as photosensitizer, consisting in Silicon Carbide (SiC) nanowires (NWs) functionalized with organic molecules (fluorinated porphyrins). Modification of the inorganic semiconductor surface with organic or bio-molecules represents the route to activate processes at the interface and can be achieved by functionalizing the SiC NWs with porphyrins, that showing a good match between the organic absorption Q band and the 3C-SiC near-band-edge- optical emission. In fact SiC NWs have interesting light emission properties [1] so it is promising the idea to couple this light emission with an organic absorber showing strong fluorescence properties, a viable route to increase the optical emission efficiency as well as to promote the anchoring of biological groups. We demonstrated the functionalization of SiOx/SiC core shell NWs, grown by a carbothermal method, showing enhanced fluorescence, with fluorinated porphyrins H2TPP(F) by supersonic molecular beam deposition (SuMBD), an approach that can promote and activate chemical/physical processes at the interface by means of the organic precursor kinetics properties [2]. The H2TPP(F)/SiC-NWs system has been deeply investigated in-situ with surface photoelectron spectroscopy and ex-situ by Cathodoluminescence (CL) to clarify the growth kinetics at low coverages and the interface processes. Results concerning the core level (C1s, Si2p, N1s, F1s) analysis at different growth steps on planar oxidized surface and SiOx/SiC core shell NWs will be presented. The role of morphology of inorganic surfaces together with kinetic activation of H2TPP(F) molecules in molecular beams will be discussed.
References: [1] F. Fabbri, F. rossi, G. Attolini, G. Salviati, S. Iannotta, L. Aversa, R. Verucchi, M. Nardi, N. Fukuta, B. Dierre, T. Sekiguchi, Nanotechnology, 21 (2010) 345702. [2] M. Nardi, R. Verucchi, R. Tubino, S. Iannotta, Phys. Rev. B, 79 (2009), 125404.
Characterisation of sub-micrometer yttrium iron garnet LPE films with low ferromagnetic resonance losses Dubs Carsten*1, Surzhenko Oleksii1, Linke Ralf1, Jauß Thomas2, Danilewsky Andreas2
1INNOVENT e.V., Technologieentwicklung, Prüssingstraße 27B, 07745 Jena (Germany) 2Institut für Geo- und Umweltnaturwissenschaften, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Str. 5, 79104 Freiburg (Germany) *email: [email protected]
Single crystalline yttrium iron garnet (YIG), which is a magnetic insulator with the smallest known magnetic relaxation parameter, appears to be a superior candidate for particle-less information transport and processing in spintronic or magnonic devices. As bulk or thick film material which is commonly grown by the liquid phase epitaxy (LPE) it has a very low damping constant, allowing magnons to propagate over distances exceeding several centimetres. But YIG functional layers and microstructures should be nanometre-thick with extremely smooth and perfect interfaces and perfect epitaxial quality. Therefore, high-quality thin YIG films were grown using different growth techniques such as magnetron sputtering, pulsed laser deposition and liquid phase epitaxy to investigate spin-wave effects [1-4, design YIG waveguides 5 as well as microstructures 6 for spin-wave excitation and propagation. In this report microstructural as well as magnetic properties of 100 nm thin YIG and La:YIG LPE films grown on (111) GGG substrates were presented. Surface roughness, crystalline perfection and compositional homogeneity were investigated by atomic force microscopy, high- resolution X-ray diffraction and X-ray photoelectron spectroscopy (XPS). Using argon-ion etching technique XPS depth profile analysis exhibit a steep transition between epitaxial film and substrate without broad interdiffusion layer. Magnetic hysteresis loops obtained by vibrating sample magnetometry show for all YIG and La:YIG films a magnetic anisotropy which is close to the ‘easy plane’ type with a typically in-plane coercive field of only 0.1 Oe. The in-plane dc-magnetized films over stripline exhibit sharp Lorentz-like absorption peaks near the frequency of ferromagnetic resonance (FMR) measured by vector network analyzer. The FMR linewidth at 6.5 GHz is estimated ΔHFWHM = 1.3 Oe that is, to our knowledge the narrowest value reported so far for YIG films with thicknesses of about 100 nm. The Gilbert damping value extracted from frequency dependent measurements were α = 1.6 10-4 which is lower than recent other reports 1-6. To compare sub-micrometer LPE films with state-of-the-art YIG films grown by gas phase epitaxial techniques key properties were compiled to show the potential of the LPE technology for sub-micrometer iron garnet film application.
References: 1 T. Liu, H. Chang, V. Vlaminck et al., JAP 115, (2014) 17A501 2 M.C. Onbasli, A. Kehlberger, D.H. Kim et al., APL Materials 2, (2014) 106102 3 C. Hahn, G. de Loubens, O. Klein et al. Physical Review B 87, (2013) 174417 4 N. Vliestra, J. Shan, V. Castel et al., APL 103, (2013) 032401 5 O. d`Allivy Kelly, A. Anane, R. Bernard et al., APL 103, (2013) 082408 6 P. Pirro, T. Brächer, A.V. Chumak et al., APL 104, (2014) 012402
Liquid phase epitaxial growth of GdAP and GdLuAP scintillating films for synchrotron imaging
Riva Federica *1,2, Douissard Paul-Antoine 1, Martin Thierry 1, Zorenko Yuriy 3, Petrosyan Ashot 4, Dujardin Christophe2
1ESRF - The European Synchrotron, 71, Avenue des Martyrs Grenoble (France) 2 ILM - Institute Lumière Matière, Université Claude Bernard Lyon 1 - CNRS, UMR 5306, Université de Lyon, F-69622 Villeurbanne Cedex (France) 3Institute of Physics, Kazimierz Wielki University in Bydgoszcz, 85-090 Bydgoszcz (Poland) 4Institute for Physical Research, Armenian National Academy of Sciences, 378410 Ashtarak-2 ( Armenia) *[email protected]
Single crystal thin film scintillators are the state-of-the-art for 2D high-spatial resolution X- ray imaging detectors. The visible image generated by a scintillator hitted by the X-rays is magnified by microscope optics and projected onto an imaging sensor [1,2]. At low X-ray energies, if a good combination of scintillator thickness, optics numerical aperture and pixel size is chosen, the spatial resolution of such a detector is only diffraction limited. Increasing the X-ray energy not only these kind of detectors suffer from low efficiency due to the low absorption in the scintillating thin film, but also the spatial resolution is limited by the spread of the energy deposition in the scintillator. Our work is related to the development by liquid phase epitaxy of single crystal thin films to improve the efficiency and the spatial resolution at high X-rays energy: new scintillators with higher absorption or higher conversion efficiency are good candidates. Aluminum perovskites present high densities and high effective atomic numbers. In particular gadolinium aluminum perovskite GdAlO3 (GdAP) and lutetium aluminum perovskite LuAlO3 (LuAP) are interesting because of their absorption k-edges located in an energy range now commonly required for synchrotrons experiments [3]. To the best of our knowledge, GdAP cannot be produced from bulk techniques with good optical quality on a large area, therefore we choose single crystal commercial YAP as substrates. We studied the condition of crystallization of GdAP and GdLuAP (GdxLu1-xAlO3) thin heteroepitaxial films with thickness from 0.5 m to 30 m, using PbO-B2O3 flux, on YAP substrates with different orientations. For imaging application, the demand in terms of crystal optical quality is high, therefore a big effort in terms of optimization of the growth conditions was needed. We studied the morphology of the film by X-ray diffraction, scanning electron microscopy and interferometric optical microscopy. A net improvement of the film quality was observed with the reduction of the lattice mismatch between YAP substrate and film, obtained introducing a fraction of Lu in the film composition. The segregation coefficient of Gd and Lu was studied for films obtained with different melt composition and different growing parameters. In order to obtains films that were suitable for imaging application, the films were doped with a small amouth of rare-earth (Ce, Tb or Eu). Results about the luminescence properties will also be shown in this presentation. Lastly, first X-ray imaging test results using these kind of scintillators will be presented.
The authors acknowledge the support of E. Ziegler for the experiments at BM05 at ESRF. A.G.P. and C.D. acknowledge the support of the Inter- national Associated Laboratory (CNRS–France & SCS–Armenia) IRMAS and of the European Union FP7/2007– 2013 under grant agreements 295025-IPERA. Y.Z. is supported by Polish NCN No 212/07/B/ST5/02376 grant agreement.
[1] A. Koch, C. Raven, P. Spanne, A. Snigirev, J. Opt. Soc. Am. A, 15-7 (1998) 1940-1951 [2] T. Martin, P-A. Douissard , M. Couchaud et al. IEEE trans. nuc. sci., 56-3 (2009) [3] P-A. Douissard, T.Martin, F.Riva et al., IEEE trans. nuc. sci., 61-1 (2013) 433-438
Controlling Polymorphism in Organic Thin Films by Light
Linus Pithan1, Caterina Cocchi1,2, Christopher Weber1, Anton Zykov1, Sebastian Bommel1,3, Steven J. Leake4, Peter Schäfer1, Claudia Draxl1,2, Stefan Kowarik1*
1 Institut für Physik, Humboldt-Universität zu Berlin, Newtonstrasse 15, 12489 Berlin (Germany) 2 IRIS Adlershof, Humboldt-Universität zu Berlin, Zum Großen Windkanal 6, 12489 Berlin (Germany) 3 Deutsches Elektronen-Synchrotron (DESY), Notkestrasse 85, 22607 Hamburg (Germany) 4 Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland; present address: ESRF - The European Synchrotron, 71 Avenue des Martyrs - CS 40220, 38043 Grenoble Cedex 9 (France) *email: [email protected]
Controlling crystallization is one of today’s challenges for high-performance organic electronic devices. We demonstrate for the organic semiconductor alpha-sexithiophene (6T) that polymorphism in molecular thin film growth can be manipulated with light. Vacuum deposited films of 6T grown on potassium chloride (KCl) exhibit a bimodal growth with two co-existing crystal phases, the low-temperature (LT) and the high-temperature (HT) 6T polymorphs [1]. We find that laser illumination (λ=532 nm, 1.5 W/cm2) during growth suppresses the formation of HT crystallites, thus the phase purity is enhanced compared to the growth without light (Figure 1a). Through x-ray diffraction experiments (Figure 1b) we are able to determine a phase coexistence ratio and find that illumination suppresses the formation of the HT phase by a factor of four. To understand the mechanism behind this optical control, we use in situ x-ray diffraction, atomic force microscopy (AFM), optical absorption measurements, as well as first-principles calculations for the optical absorption spectra of the HT and LT phase. From these we deduce that the phase purification is due to optical heating of the film and lower cohesive energy of the HT phase compared to the LT phase. This method to increase phase purity is not limited to 6T molecules, but we also present first results for a pentacene thin film demonstrating the applicability of light directed growth for a wider range of molecular materials. Our findings show that light can serve as an additional, not yet technologically used control parameter in molecular crystal growth to optimize the structural quality of organic thin films.
Figure 1. a) Sketch of the experiment: Growth of HT-phase is suppressed in illuminated substrate regions. b) XRD-scan highlighting the significant suppression of the HT crystal phase through illumination.
References: [1] L. Pithan, C. Cocchi, H. Zschiesche, C. Weber, A. Zykov, S. Bommel, S. J. Leake, P. Schäfer, C. Draxl and S. Kowarik, Cryst. Growth Des., 2015, 15 (3), pp 1319–1324
PDIF-CN2 organic thin-film deposited at room temperature by supersonic molecular beam deposition for n-type OTFT
Chiarella Fabio1*, Barra Mario1, Chianese Federico1, Toccoli Tullio2, and Cassinese Antonio1
1CNR-SPIN and Physics Department, University of Naples, Piazzale Tecchio 80, I-80125 Naples, Italy 2IMEM-CNR-FBK Division of Trento, Via alla Cascata 56/C, I-38123 Povo, Italy *email: [email protected]
The possibility to get high-mobility n-type transistors avoiding thermal treatments during or after the deposition could significantly extend the number of substrates suitable to the fabrication of flexible high-performance complementary circuits. In this contribution, we report on the fabrication of N,N’-1H,1H-perfluorobutildicyanoperylenediimide (PDIF-CN2) organic thin-film transistors (OTFT) by Supersonic Molecular Beam Deposition (SuMBD) on silicon dioxide dielectric treated with Hexamethyldisiloxane (HMDS) in the bottom contact-bottom gate configuration. The best device exhibited mobility (µ) up to 0.2 cm2/Vs even if the substrate was kept at room temperature during the organic film growth. This µ value exceeds by three orders of magnitude the electrical performance of PDIF-CN2 films grown at the same substrate temperature by conventional Organic Molecular Beam Deposition (OMBD). This achievement is possible thanks to the high kinetic energy (Ek is at most 18 eV) reached by the molecules during SuMBD process, where Ek plays very effectively the equivalent role of the substrate temperature in the OMBD technique [1]. By SuMBD, however, the PDIF-CN2 film growth turns out to be very critical with respect to the deposition parameters (in particular the deposition rate). In the figure 1, for example, it is possible to observe the critical dependence of the measured charge carrier mobility on the deposition rate assumed during the film growth. Moreover, it was observed that the reported final electrical response can be obtained only waiting for some days after the deposition. Just after deposition, indeed, these OTFT display very poor electrical performances. This effect is associated to a post deposition crystallization and molecular reorganization effect monitored through Atomic Force Microscopy and X-ray diffraction measurements.
Figure 1. Mobility extracted by OTFT trans-conductance in saturation regime for different devices obtained depositing PDIF-CN2 film at different deposition rates by SuMBD. All dashed lines are guide for the eyes.
References: [1] F. Chiarella, T. Toccoli, M. Barra, L. Aversa, F. Ciccullo, R. Tatti, R. Verucchi, S. Iannotta, and A. Cassinese APPLIED PHYSICS LETTERS 104, 143302 (2014)
POSTER S08-P01 Impact of boron on the step-free area formation during molecular beam epitaxial growth on MESA structures on Si(111)
Ayan Roy Chaudhuri*, H.-Jörg Osten and Andreas Fissel Institute of Electronic Materials and Devices, Leibniz University of Hannover, Germany *[email protected] Persistent downscaling of Si based semiconductor devices has reached to a level where the characteristic dimension of the devices will soon be comparable to the surface roughness and atomic steps on the Si wafers. Atomic steps on Si wafers which can give rise to thickness non-uniformity can drastically affect the device performance in this thickness regime. Further, electrical properties of quantum effect based emerging devices (e.g. Resonant tunnel structures) are also anticipated to be compromised by such atomic steps. In this regard presence of atomic steps and surface roughness of Si shall eventually become significant technological challenge. Since step free Si wafers cannot be manufactured, the only way to overcome this problem is to create step free areas on Si substrates. Recently, the preparation of step-free mesas on Si(111) with areas of 10m×10m by Si molecular beam epitaxy (MBE) at 1120 K has been demonstrated.1,2 Utilisation of MBE growth to prepare step free Si MESA can have advantage over the widely discussed sublimation process since this technique can limit the drawbacks (e.g. defect formation, dopant precipitation etc.) associated with the later. However, the MBE grown Si layers on top of the mesas are non-doped, which restricts the applicability of the atomically flat MESA-structures. In this study, we investigated the influence of a typical Si-dopant (Boron) on the formation of step-free areas on the MESA- structures. For comparison, the Si-MBE growth experiments were performed under the same conditions (temperature, deposition rate, deposition time) used in the earlier experiments without dopants. Two different approaches were studied. In the first approach B and Si were co-evaporated during MBE process to achieve in-situ doping. Boron co-deposition was found to drastically reduce the flat areas of only up to 1μm2. This indicates strong influence of boron on the step-flow growth behavior. In this case boron acts as surfactant3, like antimony4 which hinders the step flow growth. In the second approach boron was deposited at a lower temperature (~ 900K) prior to Si deposition which lead to the well known √3x√3 reconstruction in RHEED. Here, we have also studied the influence of boron coverage (b) within a range of 0.3 to 1 ML. Subsequent Si was grown at 1130 K on top of the √3×√3-B surface. For all the samples the √3×√3 surface reconstruction remained unchanged during and after the Si layer growth which indicates strong boron segregation under the present growth conditions. Thereby, boron should occupy only subsurface sites of the grown layer and the surface should be nearly free of Si dangling bonds at b ≥ 0.5 ML.5 In case of saturated B coverage, that means chemically passivated silicon substrate surface which behaves like a surface in the van der Waals-epitaxy.6 Therefore, the growth behaviour could be different at b ≤ 0.5 ML and b ≥ 0.5 ML. Our experiments revelaed that growth of Si on B covered MESAs results in a gradual reduction of step-free area dimension with an increase in the boron coverage. On growing ~60 nm epitaxial Si on different boron covered surface, the areas of step free regions were found to reduce from 45 m2 for b ~ 0.3 ML, to 4.5 µm2 for 0.5 ML down to 1.5 µm2 for 1 ML. This could be explained by the passivation of also step edges on Si(111) surface, which can no longer act as effective sinks for Si adatoms.7 In presence of B sub-surfactant the step edge passivation can be expected considering that pre-deposited boron segregates towards the growth front during the Si deposition. This results in a considerable increase in adatom density in front of the steps which reaches a critical value required for nucleation of Si islands (critical supersaturation). However, during the Si layer growth, boron will be also incorporated into the Si lattice up to the limit of solubility, what reduces the amount of boron available for surface dangling bond saturation. Therefore, surfactant effect becomes smaller with the lower initial boron coverage as well as with an increase in Si layer thickness. That is supported by observed increase in step-free area dimension (72 µm2) after the growth of 120 nm Si on Si MESA structures covered with 0.3 ML boron.
Acknowledgement: This work was supported financially by the Deutsche Forschungsgemeinschaft (DFG project FI 726-10)
References: 1 A. Fissel, J. Krügener, and H. J. Osten, Phys. Stat. Sol. C 9, 2050 (2012). 2 J. Krügener, H. Jörg Osten, and A. Fissel, Surf. Sci, 618, 27 (2013). 3 D. Kandel and E. Kaxiras, Phys. Rev. Lett. 75, 2742 (1995). 4 G.G. Jernigan and P.E. Thomson, Thin Sol. Films 380, 114 (2002) 5 A. Fissel, J. Krügener, D. Schwendt, and H.J Osten, Phys. Stat. Sol. A 207, 245-253 (2010). 6 J. Krügener, H.J. Osten, and A. Fissel, Phys. Rev. B 83, 205303 (2011). 7 A. Fissel, Ayan R. Chaudhuri, J. Krügener, H. Jörg Osten, J. Cryst. Growth (in press)
S08-P02 SEMIPOLAR AlN AND GaN ON Si(100): CONCEPT, HVPE TECHNOLOGY AND LAYER PROPERTIES. Bessolov1 V., Kalmykov1 A., Konenkova1 E., Kukushkin2 S., Myasoedov1 A., Red’kov2 A., Rodin1 S. 1A.F.Ioffe institute, Politekhnicheskaya, 26, St.Petersburg, 194021, phone. +7(812)2927344, e-mail: [email protected]; 2 Institute of problems of Mechanical Engineering, V.O., Bolshoj pr., 61, St.Petersburg, 199178 Introduction. The structures based on the semi-polar Gallium Nitride play an important role in production of light-emitting and laser diodes. Among different materials such as Al2O3, SiC, and Si the most promising substrate for such optoelectronic structures is Silicon due to availability of large size substrates (up to 300 mm), proper cost of manufacturing and acceptable values of thermal and electric conductivities. Technology. The semipolar GaN layers on Silicon were synthesized by combination of two consequent techniques. At the first stage the layer of SiC with the thickness of about 30 nm has been formed by solid phase epitaxy [1] on the Si(001) substrate misoriented in the (011) direction by 4–7 degrees. Then, at the second stage the buffer layer of AlN with the thickness from 300 nm up to 3 µm has been synthesized by HVPE method [2]. Thereafter the main GaN layer up to 15 µm thick has been grown. The experimental results. The half widths of rocking curves (FWHM) measured on the semipolar GaN layers obtained had the value of approximately 20–25 arcmin. Transmission electron microscopy (TEM) and Scaning Electron Microscopy (SEM) have shown that AlN and GaN layers synthesized on the misoriented Si(001) substrate have the characteristic structure of semipolar AlN and GaN (Fig.1). TEM has shown that the axis "a" of the GaN layer coincides with the Si[011] and 3C-SiC[011]directions, whereas the axis “c” is almost parallel to the Si<111> direction. However, the angle φ from the Si(001) surface normal depends on the angle of the substrate misorientation χ as φ = 55o – χ. So, φ = 510 for the semipolar GaN synthesized on the Si(001) substrate misoriented by χ=40 (Fig.2а) and φ = 480 for the misorientation χ=70 (Fig. 2b). A significant deviation (about 1.5°) between AlN[0001] and GaN[0001] directions has been detected.
(b) (а) Fig.1. TEM and SEM images of the cleveage plane (a) and the surface (b) of AlN/SiC/p-Si(100) misoriented by 4°. The main defects in a semipolar layer are basal plane staking fault and the partial dislocations bounding stacking faults (Fig.2). The relationship between the misorientation direction and the displacement vectors of the defects has been found.
(a) (b) Fig. 2. TEM image of cross-sectional GaN/AlN/3C-SiC/Si(001) heterostructure with different surface misotientation to [110] direction (a) -4 degree, (b) – 7 degree. The arrows indicate the stacking fault (SF) in GaN layers, which appears in [0001] direction. ILs – intermediate AlN and 3C-SiC layers. The model.
Structural characteristics of semipolar GaN and AlN layers synthesized by HVPE, as well as XRD data for 3C-SiC/Si(001) quasisubstrates synthesized by solid-phase epitaxy, correspond to the model, which is based on preliminary implantation into the crystals lattice of a silicon carbon atoms matrix from a carbon oxide (CO) source. In the initial formation phase C atoms occupy interstitial positions in the silicon matrix.
Fig.3. Some GaN semi-polar planes, which lie between the m- and c-planes. In the course of solid state epitaxy the activated complex transforms into silicon carbide. However, if the Si (100) plane tilted by 1-10° from <100> axis towards <011> is heated to a temperature above 600оС, the formation of steps on it will be thermodynamically favorable. It is known that the silicon lattice is most “loose” along the <011> directions, which is related to crystallographic structure of the Si lattice. CO molecules drift along this direction inside silicon lattice perpendicular to steps. As a result of Si and CO interaction the "silicon vacancy - carbon atom - silicon matrix" dipoles will be formed. Since the attraction between silicon vacancies and carbon atoms in the silicon matrix is the strongest along <011> direction, some part of the (011) Si step transforms into (111)3C-SiC step with a slope angle of ~55°. During the second stage, the semipolar AlN and GaN layers were synthesized on such 3C-SiC surfaces. Conclusion. Thus, a new approach is proposed semipolar gallium nitride layers growth on planar Si(100) substrates. This approach is based on the growth of 3C-SiC(111) layers on the misoriented Si(100) substrate by using the solid phase epitaxy and then the semipolar GaN and AlN layers are synthesized by HVPE (Fig.3). The proposed approach to preparation of thick gallium nitride layers on silicon substrate can be applied for formation of the ‘templates’ intended for fabrication of the structures for gallium nitride optoelectronics. References. [1]. S.A. Kukushkin, A.V. Osipov. J. Physics D: Appl. Phys. 47, (2014) 313001. [2]. V.N. Bessolov, E.V. Konenkova, S.A. Kukushkin, A.V. Osipov, S.N. Rodin. Rev.Adv.Mater. Sci. 38 (2014) 75.
S08-P03 Structure of AlN layer obtained by thermochemical nitriding of (0001) sapphire substrate with terrace-step surface
Vovk Olena*1, Nizhankovskyi Sergii1, Kryvonogov Sergiy1, Budnikov Olexander1, Muslimov Arsen2
1Institute for Single Crystals, National Academy of Sciences of Ukraine, 60 Lenin ave., Kharkiv, 61001 Ukraine
2Shubnikov Institute of Crystallography, Russian Academy of Sciences, 59, Leninskii pr., Moscow, 119333 Russia
*email: [email protected]
For the mass production of technical devices based on nitrides of third-group metals (GaN, InN and AlN) the great attention paid to use of modified sapphire substrates with a buffer nitride layer (GaN/sapphire or AlN/sapphire), which play a role nitride quasisubstrates. Sapphire substrates with regular nanostructures on the surface in the form of parallel terraces and steps have attractive interest for production of AlN/sapphire templates. Availability predetermined regular nanosized structure allows to reduce the probability of chaotic nucleation and nonuniform growth of the nitride layer caused mismatching parameter a of crystal lattice of AlN and sapphire (13.4 %). The initial surface of sapphire substrates (0001)±(5-15)' had terrace-step structure with step widths from 50 to 150 nm. The roughness Ra was measured to be 0.2-0.4 nm. AlN/sapphire templates was obtained by thermochemical nitridation of sapphire in a mixture of nitrogen with the gaseous reductants СО and H2 (<1 vol.%) at 1450 оС by the technique described in detail in [1]. It was established that the nitride layer repeats the terrace-step structure of the substrate surface. Thermochemical etching results in distortion of sapphire substructure. It was found the degree of distortion of the step structure and roughness of the sapphire substrate increase with increasing both the reducing potential of the medium and the annealing time.
Transmission electron microscopy of the template cross section (Fig.1) revealed the continuous aluminium nitride AlN film of thickness about 100 nm with a clear boundary AlN/Al2O3 on the surface of the sapphire substrate after thermochemical nitridation. Single-crystal phase AlN with hexagonal wurtzite structure was determined by reflection high-energy electron diffraction . Indexing of the electron diffraction pattern shows that AlN film is oriented by (0001) plane in parallel to the substrate surface and composed of blocks with small misorientation angle relative to each other. On TEM images it's clearly seen that interblock boundary begins from the edge of the step (Fig.1). The FWHM of the X-ray rocking curve of the nitride layer is 43 ang.min.
Figure 1. Cross-sectional TEM image of the sapphire substrate surface after the thermochemical nitridation. References: [1]. S.V. Nizhankovskiy, A.A. Krukhmalev, H.Sh. Kaltaev et al., Phys. of the Solid State, 54, 1896 (2012).
S08-P04 Growth of α-Cr2O3 thin films on α-Al2O3 substrate at low temperature by r.f. magnetron sputtering
Y. Gao, H. Leiste, M. Stueber, S. Ulrich
Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM-AWP), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein- Leopoldshafen, Germany
α-Cr2O3 thin films with a thickness of ~180 nm were grown on c-plane α-Al2O3 (0001) single crystal substrate at low temperature of 320 by reactive radio frequency magnetron sputtering.
The phase formation and composition was characterized by X-ray diffraction (XRD), Raman spectroscopy and Infrared spectroscopy (IR). In Bragg Brentano XRD patterns, the (0006) and (00012) reflections of rhombohedral α-Cr2O3 were identified, and the full width at half maximum (FWHM) of (0006) and (00012) Cr2O3 peaks are 0.3° and 0.8°, respectively. The rocking curve of (0006) reflex from films was performed to determine the epitaxial quality of the film with respect to the substrate. Raman and IR results confirmed the α- corundum structured Cr2O3 phase grown on α-Al2O3 substrate. Further information such as in-plane and out- of-plane lattice parameters, strain relaxation, defects, texture and orientations was obtained by reciprocal space mappings (RSMs) and pole figure measurements. The symmetric (0006) and asymmetric (10 10)
RSMs from α-Cr2O3 thin films grown on α-Al2O3 substrate were measured. The reflection from (0006) α-Cr2O3 is not exactly equal to , suggesting there is some tilt or misorientation of the α-Cr2O3 (0006) crystal plane from the α-Al2O3 (0006) plane. From the RSM measurements, lattice constants a and c of film and substrate are calculated. X-ray pole figure taken from the (0006) reflection of α-Cr2O3 films suggests the film shows a fiber texture orthogonal to the surface of the samples but with a small level of tilt. In pole figures of (10 10) reflections from the film and the substrate, six-fold symmetry reflections from α-Cr2O3 and three-fold symmetry reflections from α-Al2O3 were observed, indicating that the α-Cr2O3 films have strong texture on α- Al2O3 with rhombohedral structure and there are two different in-plane (10 10) orientations rotated by 60° domain variants. It also suggests that stacking faults are caused during the film growth.
S08-P05 n-i-p triple junction obtained by the Atomic Layer Deposition method
Sylwia Gieraltowska1*, Lukasz Wachnicki1, Bartlomiej S. Witkowski1, Marek Godlewski1,2
1Institute of Physics, Polish Acad. of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland) 2Cardinal S. Wyszynski University, Dept. of Mathematics and Natural Sciences College of Science, Dewajtis 5, 01-815 Warsaw (Poland) *email: [email protected]
An important feature of zinc oxide (ZnO) and gallium nitride (GaN) materials are their similar physical properties such as a large band gap energy of about 3.4 eV and high crystalline quality in the wurtzite structure. This opens the possibility to use them as materials for a n-p junctions for applications in optoelectronics.
We investigated the influence of interlayer (intrinsic layer) between n-type ZnO and p-type GaN on structural, electrical and optical properties of this heterostructure. Such junctions are promising structures for light-emitting diodes (LEDs) and light detectors in the range of ultraviolet radiation. This work concentrates on explanation of the influence of oxide interlayers in optoelectronic structures, and on an optimization of growth parameters (in the atomic layer deposition - ALD process) of all oxide layers. Composition of dielectric films (HfO2, TiO2, ZrO2 and Al2O3) is also optimized. The layers are used as intrinsic barriers in the n-i-p junctions. The electrical, structural and optical properties of such electronic elements can be controlled by modifying composition and growth parameters of selected oxide materials.
Our first investigations show that ZnO-based electronic structures can not only be more sensitive, but much cheaper, as well, in comparison LEDs, laser diodes based on n-GaN/p-GaN homojunctions. The intrinsic layer is able to improve the performance of the n-ZnO/p-GaN junction LEDs and realize color shift when the driving current increases and the growth parameters change. Discussion of important factors for possible manufacturing of these electronic devices will be presented underlining simplicity and low costs of our approach, as well as use of environmental friendly and low power technology.
This work was partially supported by the National Science Centre (decision No. DEC- 2013/09/N/ST5/00901).
S08-P06 2D-islands Nucleation on Si(111) at High Temperature During Sublimation and Thermal Etching by O2
Sergey Sitnikov*, Sergey Kosolobov, Alexander Latyshev
Rzhanov Institute of Semiconductor Physics Siberian Branch of Russian Academy of Sciences, pr. Lavrentieva 13, Novosibirsk, Russia, 630090 (Russia) *email: [email protected] The problem of mass transport in surface physics is of interest topic of research due to high importance for theoretical and technological applications. Atomic mechanisms of the surface diffusion play essential role in the processes of low-dimensional systems and nanoscale objects formation during MBE, gas reactions and sublimation. However, there is lack of information on the characterization of the atomic processes and diffusion parameters on the silicon surface at high temperatures; this may be due to technical difficulties in detecting of high-speed surface processes. We have used in situ ultrahigh vacuum reflection electron microscopy to investigate the process of two dimensional negative islands (etching pits) nucleation on extremely wide (up to 120μm in diameter) terraces at Si(111) surface during sublimation and thermal etching with molecular oxygen at temperatures above 1000 °C. We used classical theoretical model of nucleation [1] applied to vacancy coagulation on circular terrace, bounded by closed atomic step. By analyzing nucleation kinetics at different temperatures and comparing the results with theoretical model, we determined 2 the dominant surface mass transport mechanism. The squared critical terrace size Dcrit for nucleation of new island is found to follow power law form with scaling exponent χ changing from 0.95 to 1.15 as the temperature increased Tcrit= 1180°C. At temperatures above Tcrit we found the increasing of the critical terrace size at temperatures above Tcrit during sublimation and thermal etching by oxygen (figure 1). These findings are in agreement with previously reported step-like increasing in step spacing on Si(111) during sublimation [2]. By analyzing the kinetic of the atomic steps motion during sublimation and oxygen etching we have estimated the energy of the vacancy– step interaction EAD as 1.5±0.15 eV and the activation energy of the bulk-surface vacancy exchange process as 4,2 ±0,1 eV. We conclude that observed changes of the Dcrit in high temperature region (above Tcrit) can occur through detachment–attachment kinetics of vacancy–step exchange process rather than via surface diffusion. This work was partly supported by the Russian Foundation for Basic Researches (grant 14-08-31552) and all experiments were carried out on the equipment and under supporting of CKP “NANOSTRUKTURY”.
Figure 1. Temperature dependence of critical diameter terrace at sublimation and different rate of thermal etching with molecular oxygen.
References: [1] I.V. Markov, Acta Crystallogr. A 60 (2004) 355, [2] Y. Homma, H. Hibino, T. Ogino, N. Aizawa, Phys. Rev. B 55 (1997) R10237
S08-P07 β -Ga2O3 crystal deposition on sapphire and silicon substrates by chemical assisted vapor transport method
Pechnikov Aleksey1,3 Nikolaev Vladimir1,2,3, Maslov Viktor1,2*, Krymov Vladimir 1,2, Stepanov Sergey 1,4
Bougrov Vladislav1, Romanov Aleksey1,2,
1ITMO University, Kronverkskiypr, 49, 197101, St-Petersburg, (Russia) 2 Ioffe Physical Technical Institute, RAS, Polytechnicheskaya st., 26, 194021, St. Petersburg, (Russia) 3 Perfect Crystals LLC, Polytechnicheskaya st., 28, 194064, St. Petersburg, Russia 4Peter The Great Saint Petersburg Polytechnic University, Polytechnicheskaya st., 29, 195251, St. Petersburg, Russia
e-mail: [email protected]
Gallium (III) oxide crystals (β-Ga2O3) are currently considered as one of the most promising wide band-gap semiconductors (Eg ~ 4.9 eV). Specific advantages of this material are the transparency to the UV-C range and high breakdown voltage; at the same time, appreciable conductivity can be achieved by doping. This makes β-Ga2O3 an alternative to indium and tin oxides for transparent conductive contacts. A high-voltage transistor prototype based on gallium oxide was already demonstrated [1], an experimental batch of energy-efficient light-emitting diodes was produced [2]. Gallium oxide deposition from gallium oxide powder on silicon substrate and sapphire substrates has been studied. Gallium oxide powder is thermally evaporated from the crucible to the surface of the substrate at various temperatures (10000C-18000C) under argon. It has been found that the morphology of the films mainly depends on the substrate temperature, the deposition rate and the rate of re-oxidation. The crystallographic quality of the layers has been obtained at high temperatures for sapphire substrates. It strongly depends on orientation of sapphire substrate [3].
References: [1] E. G. Villora, Kiyoshi Shimamura, Yukio Yoshikawa, Takekazu Ujiie, and Kazuo Aoki, Appl. Phys. Lett. 92 (20), 202120 (2008). [2] H. Aida, K. Nishiguchi, H. Takeda, N. Aota, K. Sunakawa, and Y. Yaguchi, J. Appl. Phys. 47 (11), 8506 (2008). [3] V.N. Maslov, V.I. Nikolaev, V.M. Krymov, V.E. Bugrov, A.E. Romanov, Physics of the Solid State, 2015, Vol. 57, No. 7, pp. 1342–1346.
S08-P08 Dependence of the relaxation of elastic stress on the sign of strain in SiGe epitaxial layers
Novikov Alexey*1, Yurasov Dmitriy1, Shaleev Mikhail1, Yunin Pavel1
1 Institute for Physics of Microstructures RAS, 603950, GSP–105 Nizhny Novgorod (Russia) *email: [email protected]
One of the advantages of transfer from growth on Si(001) substrate to growth on relaxed SiGe buffer is the ability of formation of the layers with the different signs of strain in one structure which significantly expands the opportunities for fabrication of silicon-based devices. The deep insight of the processes of elastic stress relaxation is needed for fabrication of the SiGe heterostructures with desired parameters. However, to date the processes of plastic (via defect formation) and elastic (via development of surface roughness) relaxation of stress in SiGe layers (especially for tensile-strained layers) grown on relaxed buffers are studied much less as compared with compressed SiGe layers grown on Si(001) substrates. In the present paper the features of strain relaxation in different types of SiGe heterostructures grown by MBE on relaxed SiGe buffers were studied. Special attention was paid to investigation of the relaxation of elastic stresses in tensile GeSi layers grown on Ge(001) substrates. Usage of substrates with different lattice constants helped to reveal the influence of type of elastic strain on the SiGe growth process. It was obtained that at the same lattice mismatch between the deposited film and the substrate the thickness at which the onset of stress relaxation via development of the surface roughness occurs (critical thickness of 2D growth) is significantly higher for tensile GeSi layer than for the compressive strained layers. This effect is related with the different influence of tensile and compressive strain on the development of surface roughness on Si and Ge (2x1) reconstructed (001) surfaces [1]. Indeed according to AFM and RHEED data deposition of the tensile GeSi layers on SiGe buffer or Ge(001) substrates results in the smoothing of the surface. At the same time, the deposition of compressed SiGe layers on Si (001) substrate or on the SiGe buffer causes the development of surface roughness already at the early stages of growth, which subsequently leads to nanoislands formation. It was obtained that the critical thickness of 2D growth of tensile-strained GeSi layers on Ge(001) substrate is higher than the critical thickness of their pseudomorphic growth (critical thickness at which the plastic relaxation occurs). As a result, growth of the coherent self-assembled quantum dots cannot be achieved in the case of GeSi/Ge(001) tensile-strained structures. It was demonstrated that the ability of formation of layers with the different signs of strain in the case of growth on relaxed SiGe buffer gives the additional opportunities to control the growth of strained SiGe heterostructures [2]. In particular, the predeposition of a thin tensile strained layers significantly increase the critical thickness of 2D growth of compressed SiGe layers on relaxed buffer [2]. The work was supported by RFBR (grants # 13-02-01006-а, 14-02-01116-а and 13-02- 12108-ofi_m) and the Scholarship of President of Russian Federation for young scientists SP- 5485.2013.5.
References: [1] Xie Y.H., Gilmer G.H., Roland C., Silverman P.J., Buratto S.K., Cheng J.Y., Fitzgerald E.A., Kortan A.R., Schuppler S., Marcus M.A., Citrinet P. H. al., Phys. Rev. Lett. 73 (1994) [2] Shaleev M.V., Novikov A.V., Yurasov D.V., Hartmann J.M., Kuznetsov O.A., Lobanov D.N., Krasilnik Z.F., Appl. Phys. Lett. 101 (2012) 151601
S08-P10 Influence of thermal treatment on the optical and electrical properties of ZnO:B thin films Kh.A. Abdullin1, L.V. Gritsenko1,2*, N.R. Guseinov1, D.V. Ismailov1, Zh.K. Kalkozova1, S.E. Kumekov2, Zh.O. Mukash2, E.I.Terukov3
1Kazakh National University after al_Farabi, al_Farabiave. 71, Almaty, Kazakhstan
2Kazakh National Technical University after K.I. Satpaev, Satpaev str., 22, Almaty, Kazakhstan
3Ioffe Physico-Technical Institute, 26 Politekhnicheskaya, St Petersburg, Russian Federation *[email protected]
Zinc oxide (ZnO) has unique properties, such as wide band gap ~ 3.37eV, a large exciton binding energy (~ 60 meV), and effective ultraviolet photoluminescence, what makes it attractive for practical applications. Currently ZnO is one of the most actively studied wide-band semiconductor materials. Zinc oxide is promising to create a new generation of bright optoelectronic devices such as light-emitting diodes, based on heterostructures and homostructures, due to a large exciton binding energy. Today, the zinc oxide is used in the short-wavelength LEDs [1], detectors, piezoelectric devices [2], sensors [3], power electronics, in dye solar cells, and in many other applications. In particular, boron doped ZnO thin films, are used as the transparent and conductive front contact of solar cells. The temperature of samples increases during the treatment and exploitation. It leads to the changes of ZnO films properties and can adversely affect on the devices performance. Therefore, the study of the electrical and optical properties modification exposed to the heat treatment is an important task for application of thin films in optoelectronics and solar cells. Experimental results on optical and electrical properties of ZnO:B thin films deposited by MOCVD on the glass substrates are presented in the report. The effect of thermal treatment in air and in vacuum on a change of optical properties (absorption and transmission spectra, Raman scattering, photoluminescence − PL) and electrical properties (concentration and carrier mobility, as well as the resistivity) of ZnO:B samples was studied. It was found that the optical absorption near band gap increases with increasing annealing temperature of the samples. Excitonic PL band intensity increases under annealing approximately in three times. Annealing of ZnO:B samples at temperatures above 200°C leads to the degradation of electrical properties: carrier concentration as well as mobility decrease, while the resistivity increases. Subsequent annealing of samples in vacuum at 450-500°C causes significant recovery of electrical parameters.
References: [1] Zhong Lin Wang, Mater Today, 7 (2004) 26. [2] De Sousa V. C., Morelli M. R., Kiminami G. A., Castro M. S., Journal of materials science: Materials in electronics, 13 (2002) 319. [3] S. K. Gupta, Aditee Joshi and Manmeet Kaur, J. Chem. Sci., 10 (2010) 57.
S08-P11 Preparation and optimization of a molybdenum electrode for CIGS solar cell Feng Jingxue2, Zhuang Lin*1, Wang Xin2, Hong Ruijiang1, Shen Hui1
1. School of Physics and Engineering, Institute for Solar Energy Systems, State Key Laboratory of Optoelectronic Materials and Technologies, Guangdong Provincial Key Laboratory of Photovoltaics Technologies, Sun Yat-Sen University, Guangzhou 510275, P. R. China
2. School of Materials Science and Engineering, South China University of Technology, Guangzhou 510275, P. R. China
Referring author: Sun Yat-Sen University, Zhuang Lin E-mail address: [email protected]
Single molybdenum(Mo) films were deposited by radio frequency (RF) and direct current (DC) magnetron, respectively. With changing the deposition parameters including deposition pressure, power and substrate temperature, the films show different surface morphology and crystallinity. A lower resistivity and better crystallinity are obtained in the DC mode. It is shown that both the crystallinity and grain size increase when the deposition pressure decreases. The crystallinity has no significant changes when the deposition power varies from 100 to 200 W. With the substrate temperature increases, the porosity and grain size of the Mo films increase. After the films were annealed in furnace with inert Ar gas, the Mo films show denser structure and lower hole content. The cross-sectional view of the Mo films has a columnar morphology, which indicates the films have high crystallinity. The XRD result indicates that the crystallinity of the films has a strong preferential orientation along the (110) plane in DC mode, which is shown in Fig.2. The lowest resistivity of the single Mo film is 34×10-6 Ω·cm when the deposition pressure is 0.1Pa and the deposition power is 300 W in DC mode. In order to obtain lower resistivity and better adhesion, a three-layer film is deposited in DC and DC/RF mixed mode. The three-layer film shows good adhesion and a low resistivity of about 50×10-6 Ω·cm, which is appropriate for CIGS solar cell.
Fig1 Fig2
Fig1. The cross-sectional view of the single Mo films Fig2. Typical XRD spectra of DC and RF magnetron sputtered molybdenum thin films at 0.6Pa
S08-P12 Surface induced weak orientational order and role of isotropic nematic- interface fluctuations in the appearance of an induced nematic film Elena S. Pikina1,2,* , Charles Rosenblatt3 111 Oil and Gas Research Institute, Russian Academy of Sciences, 119333 Moscow, Russia
2 Landau Institute for Theoretical Physics of the RAS, 142432 Chernogolovka, Russia 3Department of Physics, Case Western Reserve University, Cleveland, Ohio, USA Recently the nontrivial spatial and temperature dependence of the surface-induced weak planar orientational order parameter Q(z,T) was determined experimentally just above isotropic-nematic (IN) phase transition point [1]. The experiment was performed by immersing a highly tapered optical fiber into a thin liquid crystal layer and measuring the optical retardation between the aperture and substrate as a function of height. The most intriguing features of these results are that Q is considerably smaller than the bulk order parameter discontinuity QIN at the IN phase transition and at all reduced temperatures t=(T-TIN)/(TIN-T*) Q(z) does not decay exponentially, but instead exhibits a “shoulder” extending to about 30 nm from the substrate before decaying rapidly in space over an IN-interfacial coherence length of order 5-7 nm. Here we present a theoretical explanation of the observed behaviour. We obtain expressions for the short-range and long-range contributions to the interface potential of the induced nematic film and demonstrate the repulsive interaction between the soft IN-interface and the bounding substrate. We propose a method to determine the nematic order parameter profile in the induced nematic film using the numerical shooting method. Thereafter the bare short-range repulsive interaction in these films is calculated by introducing a model nematic order parameter profile. The bare nematic director thermal fluctuation-induced long-range repulsive interaction between the weak IN-interface and bounding surface - the so called “pseudo-Casimir interaction” - is obtained using a functional integral approach. It is shown that the small value of the IN-interfacial tension results in the renormalization of the repulsive interaction potential due to the thermal fluctuations of the soft IN-interface. This leads to an increase of the equilibrium thickness of the induced nematic film and appearance of a step-like orientational order parameter profile. We find that only renormalized short-range and thermal pseudo-Casimir interactions are essential for the appearance of the induced nematic film, which provide the observed thickness about 30 nm. The long-range van der Waals interaction is shown to be negligibly small and the dominant role is played by the renormalized short- range repulsion. As a result, the experimental dependences of the nematic order parameter amplitudes [1] can be fitted with good accuracy, Fig.1. The fitting makes it possible to determine the material parameters of the system, including the amplitudes of the surface interaction, the IN-interfacial tension and the interfacial coherence length. Reference: [1] E. Pikina, C. Rosenblatt, Eur. Phys. J. E , 35, 87 (2012). [2] J.-H. Lee, T.J. Atherton, V. Barna, A. De Luca, E. Bruno, R.G. Petschek, and C. Rosenblatt, Phys. Rev. Lett. 102, 167801 (2009).
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* presenting author; E-mail: [email protected]
S08-P13 Effects of thermal annealing on AlInGaN/AlN/GaN heterostructure grown by MOCVD
R. Loganathan*1, P. Dhivya Maria Pushpam1 R. Ramesh and K. Baskar1
1Crystal Growth Centre, Anna University, Chennai-25 (India) *email: [email protected]
Group III nitrides such as GaN, AlN and InN are wide bandgap semiconductors that have attracted great interest in optoelectronics, high power and high frequency device applications due to their high thermal stability, high carrier mobility and direct bandgap. Usually nitride based devices are grown heteroepitaxially on a number of foreign substrates. Difference in the lattice parameter and thermal expansion coefficient between the substrate and the epilayer cause poor crystalline quality by introducing defects and cracks into the material. For a high quality device performance, a material with good crystalline nature is required. Since thermal annealing is used as a processing step in the fabrication of nitride based devices, it is used as a technique to improve the quality of lattice mismatched layers [1][2]. In this study, nearly lattice matched AlInGaN/GaN heterostructure have been grown epitaxially by Metal Organic Chemical Vapor Deposition (MOCVD) on Sapphire substrate with varying indium composition from 3% to 5% with constant flow rates of TMGa and TMAl [2]. The as grown samples were annealed in a tubular furnace ranging from 850°C to 950°C in steps of 50°C for 20-50 min in nitrogen ambiance. The samples were characterized before and after annealing process, the morphological changes were studied with Atomic Force Microscopy (AFM) to find the root mean square (RMS) roughness. The crystalline quality and composition were determined by HRXRD. The composition of as grown AlInGaN has been estimated from omega/2theta scan and simulation fit [Fig.1]. Reciprocal Space Mapping (RSM) was used to study the strain and relaxation between the AlInGaN/GaN heterostructure. The optical properties have been investigated by photoluminescence. The results have been discussed in detail.
Figure 1. Omega/2theta scan of AlInGaN/GaN heterostructure References: [1] R. Loganathan, M. Balaji, K. Prabakaran, R. Ramesh, M. Jayasakthi, P. Arivazhagan, Shubra Singh and K. Baskar., Journal of Material Science: Materials in Electronics, (2015) DOI 10.1007/s10854-015-3082-4. [2] J.P. Ahl, J. Hertkorn, H. Koch, B. Galler, B. Michel, M. Binder, B. Hollander. J. Cryst. Growth, Vol. 398 (2014) pp. 33-39.
S08-P16 Growth and Optical Investigation on InGaN/GaN Quantum well Structures grown by Metal Organic Chemical Vapour Deposition
Kandasamy Prabakaran*1, Raju Ramesh1, Eric Faulques2, Krishnan Baskar1
1Crystal Growth Centre, Anna University, Chennai, Tamilnadu (India) 2Institute of Materials Jean Rouxel, University of Nantes, Nantes (France) *email: [email protected]
The InGaN/GaN Quantum Well structures were grown on c-plane sapphire substrate using metal-organic chemical vapor deposition (MOCVD). Crystalline quality has been investigated using High-resolution x-ray diffraction analysis and total dislocation densities of screw and edge types in the GaN epilayer have been calculated [1]. The thickness and indium composition of the InGaN was determined by HRXRD. From simulation fit, the composition of indium was found to be 10-15% and thickness was around 5 nm and 10 nm . Surface properties of the samples have been analyzed using Atomic force microscopy (AFM) and Scanning Electron Microscopy (SEM) respectively. Energy Dispersive X-ray analysis (EDX) technique was applied to study the distribution of Indium composition in the InGaN/GaN Quantum Well Structures. Room-temperature time-resolved photoluminescence, photoluminescence (Figure. 1(a-c)) and Raman spectroscopy measurements have been performed on InGaN/GaN Quantum Well Structures. The photoluminescence intensity was degrades with increases of InGaN thickness and the results were discussed in detail.
Figure.1. Time Resolved Photoluminescence and Photoluminescence Spectra of InGaN with different thickness and composition
References: 1. Kim, H. J., Liu, J., Zhao, Z. M., & Xie, Y. H, Journal of Vacuum Science & Technology B, 22(4) (2004) 2257-2260.
S08-P17 Synthesis and thin films growth of BaBiO3, Ba1-xKxBiO3 and BaBiO1-yFz compounds by pulsed laser deposition
Gawryluk Dariusz Jakub*1, Ristic Zoran1,2, Shi Ming1, Radovic Milan1, Plumb Nicholas1, Shiroka Toni3, Mesot Joël1,3, Medarde Marisa1, Pomjakushina Ekaterina1, Conder Kazimierz1
1Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland) 2Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne (Switzerland) 3Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich (Switzerland) *email: [email protected]
Barium bismuthate - BaBiO3 (BBO) was identified as a charge-ordered insulator or Peierls semiconductor [1] with a charge Bi3+/Bi5+ disproportionation [2] and a charge density wave ordering (CDW) [3]. However, hole-doped Ba1-xKxBiO3 (BKBO) with ~ 0.37 ≤ x < ~ 0.5 is known as a metallic compound showing superconductivity at ~ 30 K [4]. Very recently, it was theoretically predicted that the parent compound BBO, potassium doped BKBO and also electron-doped BaBiO1-yFz (BBOF) are possible topological insulators with a large energy gap [5] or even 2D superconductors [6]. We decided to study all these intriguing properties on heteroepitaxial films growth by the Pulsed Laser Deposition (PLD). For these studies BBO, BKBO and BBOF targets have been prepared. Chemical compositions of the targets were measured by the X-Ray Fluorescence (XRF) and oxygen stoichiometry by the Termogravimetric Analysis (TGA). Crystallographic purity was checked by the X-Ray Diffraction (XRD). Rietveld analyses of the obtained XRD patterns were performed. Magnetic properties of the samples were studied using Superconducting Quantum Interference Device (SQUID) magnetometer and Physical Property Measurement System (PPMS). Films of BBO and BKBO were deposited on (100) MgO substrates. Structural and surface quality of the films was in-situ monitored using Reflection High Energy Electron Diffraction (RHEED). Structural (XRD), electrical (PPMS) and magnetic (SQUID) measurements were performed on the series of the obtained films.
Figure 1. RHEED pattern from of the BBO thin film grown on MgO
References: [1] Sleight A. W., et al., Solid State Commun., 17 (1975) 27. Tajima S. et al., Phys. Rev. B, 32 (1985) 6302. Lobo R. P. S. M. et al, Phys. Rev. B, 52 (1995) 13294. Franchini C. et al, Phys. Rev. B, 81 (2010) 085213. [2] Cox D. E. et al., Solid State Commun., 19 (1976) 969. Harrison W. A., Phys. Rev. B, 74 (2006) 245128. [3] Wei X. et al., Solid State Commun., 81 (1992) 419. Kim H.-T., Phys. Rev. B, 54 (1996) 90. Hase I. et al., JPCS, 108 (2008) 1. [4] Cava R. J. et al., Nature, 332 (1988) 814. Hinks D. G. et al., Nature, 333 (1988) 869. [5] Jin H. et al., Sci. Rep., 3 (2013) 1. Yan B. et al., Nature Phys., 9 (2013) 709. Li G. et al., Scientific Reports, 5 (2015) 10435. [6] Vildosola V. et al., Phys. Rev. Lett., 110 (2013) 206805. [16] A. Taraphder et al., Europhys. Lett. 21, 79 (1993).
S08-P18 Properties of Crystalline Silicon Layers for Photovoltaic Application grown on Glass by Steady-State Solution Growth
Christian Ehlers*, Roman Bansen, Jan Schmidtbauer, Franziska Ringleb,
Thomas Teubner, and Torsten Boeck,
Leibniz-Institut für Kristallzüchtung, Max Born-Str. 2, 12489 Berlin (Germany)
*email: [email protected]
Silicon thin film solar cells require only several ten micrometers of crystalline silicon to absorb sunlight efficiently. We developed a two-step process for depositing silicon on low cost glass substrates to meet those demands. Initially a seed layer of silicon is deposited on heated glass substrates by two different approaches. Either only a thick amorphous silicon layer is deposited by physical vapor deposition, or a metal such as tin is evaporated afterwards which results in the metal-induced recrystallization of a thin amorphous silicon layer. In the second step, a silicon layer is grown epitaxially on the seed layer by steady-state solution growth from a tin solution keeping the temperature below the softening point of glass. Unlike common liquid phase epitaxy where the growth process is driven by uniform cooling and subsequent supersaturation of the metallic solvent, here a permanent temperature gradient between the silicon source material and the glass substrate floating on the solution is employed. Therefore, our process has substantial similarity to a conventional float glass production-process which would allow for the deposition of silicon on glass in a continuous way. We will present electrical and structural properties of the grown silicon layers and discuss their suitability for solar cell devices.
S08-P19 CdHgTe deposited on CdZnTe substrates by Closed Space Sublimation technique
S. Rubio, E. Repiso, A. Corrochano, M. Sochynskyi, J L. Plaza, E. Diéguez
Laboratorio de Crecimiento de Cristales, Universidad Autónoma de Madrid, Madrid, (Spain)
CdHgTe (CMT) is semiconductor material of great significance for the development of IR detectors due to the fact that this material covers the IR range [1]. CMT epitaxial layers were deposited on CdZnTe (CZT) substrates for the development of these devices. The use of CZT crystals as substrates is due to lattice matched of CMT with CZT [2]. Usually, CMT layers are growth by different deposition techniques such as Liquid-Phase Epitaxy (LPE) and Molecular Beam Epitaxy (MBE) [3], [4]. In this work, CZT crystals has been studied in order to be employed as substrates in CMT/CZT devices, later epitaxial layers of CMT have been deposited on CZT substrates by Closed Space Sublimation (CSS) method, this deposition technique allows to develop layers at lower temperature that the CdHgTe melting point and not required the use of ultra-high vacuum (UHV). CMT and CZT crystals were employed as source and substrate material respectively. CZT crystals were sliced and mechanically polished using different Al2O3 grain size. Before performing the CMT deposition, CZT substrates were subjected to a chemical cleaning. The CMT layers were deposited by Closed Space Sublimation technique about 500ºC for an average of 5 min being the distance from the source to substrate between 1 - 3 mm and the chamber pressure base was 1 mbar. Different characterizations in the CZT substrates and CMT/CZT samples were carried out in order to study the crystal structure, chemical composition, IR transmittance and morphology by X- Ray Diffraction (XRD), Energy Dispersive X-Ray Spectroscopy (EDX), Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Total reflection X-Ray Fluorescence (TXRF), Fourier Transform InfraRed spectroscopy (FTIR) and Scanning Electron Microscope (SEM). The chemicals analyses carried out in the CZT substrates show a concentration of Zn close to 4%. Furthermore, the XRD and FTIR spectrums indicate that main orientation is (111) and the transmittance is higher than 55% in the infrared range. The CMT layers deposited on CZT present good homogeneity being their chemical composition 49.9at%, 49.4at% and 0.7at% for Cd, Te and Hg respectively.
Figure 1. X-Ray Diffraction (XRD) spectra of CZT substrate
References: [1]Tonheim, C. R., Sudbo, A. S., Selvig, E., & Haakenaasen, R. ,IEEE Photonics Technology Letters, 23, (2011). 36-38. [2] Skauli, T., Colin, T., Sjølie, R., & Løvold, S., Journal of Electronic Materials, 29 (2000) 687-690. [3] Gravrand, O., & Destefanis, G., Infrared Physics & Technology, 59 (2013) 163-171. [4]Belogorokhov, A. I., Smirnova, N. A., Denisov, I. A., Belogorokhova, L. I., & Levonovich, B. N. Physica status solidi , 7, (2010) 1624-1626.
S08-P22 Growth and luminescent properties of single crystalline films of Ce3+ doped Gd1-xLuxAlO3 and Pr1-xLuxAlO3 perovskites
Yu. Zorenko1,2, T. Zorenko1,2, V. Gorbenko1,2, T. Voznyak2, A. Fedorov3, A. Suchocki4, Ya. Zhydachevski4
2Institute of Physics, Kazimierz Wielki University in Bydgoszcz, 2 Powstańców Wielkopolskich str., 85090 Bydgoszcz (Poland) 2Electronics Department, Ivan Franko National University of Lviv, 5 Dragomanova str.,79017 Lviv, Ukraine 5Institute for Single Crystal NAS of Ukraine, 60 Lenin av., 61178 Kharkiv (Ukraine) 3Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland) *email: [email protected] The liquid phase epitaxy (LPE) technology offers the possibility of obtaining the high–density single crystalline film (SCF) scintillators based on different oxide compounds [1, 2]. Namely, SCF screens play a key role in 2D/3D detectors used for imaging applications at X-rays synchrotrons [2]. RAlO3 perovskites (Lu, Gd, Pr and their combination) are good candidates for high-efficient SCF screens due to their high densities and effective atomic number [3]. Apart from that, the absorption K- edge of these compounds is located in an energy range where imaging applications is possible as well. 3+ The results of composition engineering and luminescent properties of Ce doped Pr1-xLuxAlO3 (PrLuAP) and GdxLu1−xAlO3 (GdLuAP) SCF have been presented in this work. We have used the following research concepts: (i) “Ce3+ ion energy level positioning” [4]; (ii) “band gap engineering” 3+ [5] and (iii) “enhancing the energy transfer from the host to Ce ion”, which are applied to YAlO3:Ce (YAP:Ce) scintillation material by the introduce of Gd3+ and Pr3+ ions into the cub-octahedral sites of perovskite host in the concentration ranges x=0÷1.0 and x=0÷1.5, respectively. Firstly, we search for the conditions of LPE growth of the SCFs of GdLuAP and PrLuAP perovskites on cheap YAlO3 (YAG) substrate using the PbO-B2O3 based flux and found that the full set of GdxLu1−xAlO3 SCFs with x values in x=0÷1.0 range and sets of PrxLu1−xAlO3 SCFs with x values in x=0÷0.5 range can be successfully crystallized onto the same YAP substrates. The luminescent properties of Ce3+ doped GdLuAP and PrLuAP SCFs were studied by traditional spectroscopic methods, such as absorption, cathodoluminescence, light yield measurements under α- particles excitation and photoluminescence under excitation in the Ce3+, Pr3+ and Gd3+ related bands. Namely, we have demonstrated the efficient Gd3+→Ce3+ energy transfer in GdLuAP SCF and the efficient Pr→Ce energy transfer in PrLuAP SCF. The efficiency of the energy transfer in GdLuAP and 6 PrLuAP SCF with different Gd and Pr content strongly depends on the energy matching of Pj level of Gd3+ cations or 5d1 levels of Pr3+ cations with 5d1 one of Ce3+ ions. For studying the Pr-Ce energy transfer in perovskite host we have also performed the luminescent spectroscopy of Pr-Ce doped YAP sample under excitation by synchrotron radiation at the Superlumi station at HASYLAB, DESY. We have also found the significantly larger influence of Pb2+ flux related impurity on the LY of Ce3+ emission in GdLuAP and PrLuAP SCF, in comparison with the YAP:Ce SCF, grown onto YAP substrates. This effect is caused by the larger lead contamination in SCF of Gd-Pr based perovskites, in comparison with the YAP counterpart due to the relatively larger dimension of the sites of perovskite hosts, where the Pb2+ ions are localized. Thus, it is desirable to use the lead-free fluxes for producing the SCF scintillators based on the multicomponent perovskites to achieve their higher LY. References: [1] Yu. Zorenko, V. Gorbenko, T. Martin, P.‐A. Douissard, , et all, Radiation Measurements 56 (2013) 415. [2] Т. Мartin, A. Koch, Journal of Synchrotron Radiation, 13 (2006) 180. [3] P.‐A. Douissard, T. Martin, F. Riva, Y. Zorenko, et all, Proc. SCINT2015 conference, San‐Francisco, 2015. [4] K. Kamada, T. Endo, K. Tsutumi, J. Pejchal, M. Nikl, K. Tsutumi, et all, Cryst. Growth Des., 11 (2011) 4484. [5] Fasoli, M., Vedda, A., Nikl, et al., Phys. Rev., B 84, 081102(R) (2011).
This work was realized within the Polish NCN No 2012/07/B/ST5/02376 and Ukrainian SL-20F projects.
S08-P25 Strained Ge layers on virtual Si1-xGex(001) substrates
J. Schmidt*1, D. Tetzlaff1, E. Bugiel1 and T.F. Wietler1,2
1Institute of Electronic Materials and Devices, Leibniz Universität Hannover, Schneiderberg 32, D-30167 Hannover, Germany 2Laboratory of Nano and Quantum Engineering, Leibniz Universität Hannover, Schneiderberg 39, D-30167 Hannover, Germany *email: [email protected]
Strained Ge layers have become very interesting for their use in high mobility channels for modern metal oxide semiconductor field-effect transistors (MOSFETs) [1]. Due to the large lattice mismatch between Ge and Si (~ 4.2%), the use of a virtual substrate (VS) is required in order to grow pseudomorphically strained Ge layers of higher thickness. In contrast to conventional methods like graded buffers, the use of surfactant-mediated epitaxy (SME) using Sb as a surfactant provides smooth, fully relaxed virtual substrates with a thickness of 500 nm [2]. Based on an adapted model for the system Si1-xGex/Si, we calculated the critical thicknesses for elastic and plastic relaxation for the system Ge/Si1-xGex. In good agreement with those theoretical considerations, we observe the beginning of plastic relaxation via the formation of misfit dislocations after reaching a critical layer thickness regarding the force-balance model [3]. By varying the composition of the VS, the critical thickness for strained Ge layers can be tuned, making it applicable for high mobility channels. Ge layers were grown on relaxed virtual Si1-xGex(001) substrates using SME. The samples were characterized with HRXRD, GIXRD, TEM, SEM, AFM and Raman spectroscopy. For Ge on Si0.22Ge0.78, it is between 10 and 20 nm and for Ge on Si0.31Ge0.69 between 5 and 10 nm, respectively. TEM investigations show relaxation of the layers via the generation of misfit dislocations (MDs) after reaching the critical thickness, confirming the change in lattice parameters acquired by HRXRD / GIXRD (Fig. 1). Regarding surface morphology, the need for a surfactant is confirmed to grow smooth layers. The surfactant decreases the surface free energy of the film and reduces the diffusion length of adatoms on the surface, thereby suppressing the island growth that would otherwise occur at the chosen process temperature.
Figure 1. TEM weak beam dark field images of defect structures of SME-Ge/Si0.22Ge0.78 systems with different Ge layer thicknesses. The onset of plastic relaxation via MD formation is observed.
References: [1] M. L. Lee et al., J. Appl. Phys. 97(1) (2005) 011101. [2] T.F. Wietler et al., Thin Solid Films 557: (2014) 27–30 [3] J. W. Matthews and A. E. Blakeslee., J. Cryst. Growth 27 (1974) 118 – 125.
S08-P26 Reconstruction phase transition c(4x4) - (1x3) on the (001)InSb surface
Bakarov Askhat*1, Galitsyn Yurij1, Mansurov Vladimir*1, Zhuravlev Konstantin1
1Rzhanov Institute of Semiconductor Physics, ac.Lavretiev avenue, 13, Novosibirsk (Russia) *email: [email protected], [email protected]
The (100) surface of InSb is the most common growth surface, forming a number of surface reconstructions depending both on the ratio of the group III and V species present on the surface and the substrate temperature. Compared to the more commonly studied GaAs(100) surface, studies of the epitaxial growth and reconstructions of InSb(100) are relatively scarce. In the present work the surface structures that are formed have been observed, using reflection high energy electron diffraction (RHEED), both during epitaxial growth and under static conditions (i.e. under Sb flux only). The observed surface structures are include a (4x3), a (7x5), a c(4x4) and an asymmetric (1x3). Usually the epitaxial growth is started on the c(4x4) surface (under Sb flux) and the surface structure is transform to (1x3) reconstruction after onset of the In flux. The reconstruction phase transition c(4x4) - (1x3) is investigated in details as a functions of the substrate temperature and of the Sb flux. The intensity of inherent fractional spots of the c(4x4) phase was measured during variation of these parameters. It was experimentally found that at temperatures T<395°C there is a clear hysteresis for the isotherms recorded during direct and reverse Sb flux variation, as it shown in Figure 1, i.e. there is an evidence that the transition c(4x4) - (1x3) is discontinuous (first order transition). However, the hysteresis is not observed at temperatures T>395ºC (see Figure 1, the isotherm at 402ºC). Previously, the transition c(4x4) - (1x3) was discussed in the work [1] as a continuous order- disorder transition, and authors have reported 3 critical temperatures for the 3 different fluxes of Sb. However, it is clear that the transition is induced by the Sb adsorption onto the surface and only one critical temperature exists. We have developed a model to describe the transition in frame of the lattice gas approximation. This model takes into account the stabilization energy as result of Sb dimers formation on the c(4x4) phase and lateral repulsion between the nearest neighboring Sb dimmers.
Figure 1. Phase transition c(44) - (14) as function of Sb flux at different temperatures. Theta – the coverage of the InSb surface by Sb dimmers. The research was supported by a grant of Ministry of Education of the Russian Federation RFMEFI60414X0134.
References: [1] Nigel Jones, PhD thesis, “The Atomic Structure of the Indium Antimonide (001) Surface”, Department of Physics and Astronomy University of Leicester. (1998) pp.102-120.
SESSION 9
Fundamentals - Structural Defects and their characterization in Crystalline Materials
Cellular dislocation patterns in “Mono-like” silicon grown by seeded directional solidification of the melt
Vanessa Amaral de Oliveira12*, Marina Rocha1, Thu-Nhi-Tran-Thi3, Maria Tsoutsouva3, José Baruchel3, Denis Camel1
1Université Grenoble Alpes, CEA-INES, Savoie Technolac, F-73375 Le Bourget-du-Lac (France) 2 ECM Greentech, 109 rue Hilaire du Chardonnet, 38100 Grenoble (France) 3European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex 9 (France) *email: [email protected] Mono-like silicon growth has recently been established as a low cost alternative for the growth of monocrystalline ingots. With the use of an extended monocrystalline seed layer at the bottom of the crucible, silicon grows by directional solidification with the same orientation of the seeds. Despite the best mono-like solar cells achieve efficiencies close to Cz-Si based cells, average mono-like Si efficiencies are still limited by the presence of structural defects such as dislocations. Dislocations arranged in cellular patterns can be observed in the entire mono-like Si ingot. This cellular structure is composed by dense walls of immobile dislocations formed by cross-slip and short range interactions between dislocations. The walls are separated by almost dislocation free domains including few mobile dislocations produced by deformation that will be blocked or annihilated at the dislocated wall during annealing at high temperature. P. Rudolph [1] studied this structure in as-grown semiconductor crystals and correlated the cell dimension with the dislocation density and the local thermo-mechanical stress. It was also observed that doping (for instance with In in GaAs) can lead to the suppression of those cellular patterns [2]. In the present work, Synchrotron radiation X-ray White-beam Topography and Rocking Curve Imaging (RCI) is applied to visualize the dislocation arrangements and to quantify the spatial distribution of the associated lattice distortions. RCI peak position mapping shows a very small crystal mosaicity with tilt angles between cells smaller than 3 arcseconds. The cells are present in higher densities inside the seeds (cell diameter of 300 µm and dislocation density estimated as 105 cm-2 in its wall). As growth proceeds, the cell size increases and the dislocation density decreases varying from 5 × 104 cm-2 to 1 × 104 cm-2 according to the zone of the ingot. In order to understand the influence of parameters as silicon doping, stress and time under stress on the formation of cells, a comparative study was started on the dislocation structures obtained by crystallization of conventional as well as Ge doped (1020 at.cm-3) Si ingots, and by annealing under imposed stress with a 4- point bending test device accommodated inside a DSS furnace. The bending tests were carried with specimens of pure and Ge-doped silicon single crystals at 1300°C, using stress of 1 MPa and 5 MPa and time under stress of 2h and 10h. The first results show changes in the cellular network in Ge-doped silicon, probably related with local lattice deformation that affects the dislocation dynamics. On this basis, a discussion is made of the dynamics of formation of the final dislocation arrangement.
a) b)
c)
100 µm
1 mm
Figure 1. a) Cellular patterns in the bottom of a mono-like ingot. b) Cell structure visualized by RCI. c)RCI integrated intensity change at cell walls (higher intensities) and at cell core (lower intensities).
References: [1] P. Rudolph., Cryst. Res. Technol. 40, No. 1/2, (2005) 7-20 [2] H. Ono., Journal of Crystal Growth.89 (1988) 209-219
Nonstoichiometry problems of AIIBVI vapor grown crystals
Igor Avetissov*1, Andrew Khomyakov1, Albert Davydov2, Elena Mozhevitina1, Vladimir Chegnov2, Nikolai Zhavoronkov2
1D.Mendeleyev University of Chemical Technology of Russia, Miusskaya pl.9, Moscow (Russia) 2 Research Institute of Material Science and Technology, Proezd 4806, build.2, Zelenograd Moscow (Russia) *email: [email protected]
AIIBVI single crystals have a number of unique properties which significantly depend on nano- scale defect type and concentration. Native point defects generating as a result of deviation from stoichiometric composition influence on luminescence, conductivity, and other structure sensitive properties in the same manner as dopants. Raising the level of purity of modern semiconducting materials results to the need of nonstoichiometry control in single crystals, thin films, polycrystalline powders, etc. At the same time the new level of purity of semiconductors needs to check and revise the literature data of nonstoichiometry. In the research we have examined extra pure 50-100 mm diameter CdTe, ZnTe, ZnSe, CdSe, CdS single crystals grown from vapor by Davydov-Markov technique [1]. Impurity and nonstoichiometry distributions have been analyzed by ICP-MS and «extraction» techniques [2], correspondingly. The correlation between equilibrium P-T-x diagrams and crystal's nonstoichiometry has been discussed. It was proved that in some cases the electrically neutral native point defects were dominant in the analyzed crystals. The generalized scheme of nonostoichiometic defects in AIIBVI compounds has been elaborated.
Figure 1. ZnTe, CdTe and ZnSe single crystals grown by Davydov-Markov technique [1]
References: [1] Davydov A., Markov E., Khryapov V., Izvestia Akad. Nauk SSSR, Neorg. Mater. 16(12) (1992) 2119 [2] Avetissov I., Mozhevitina E., Khomyakov A., Tran Khanh, Cryst. Res. Technol. 50 (2015) N 1, 93–100
Influence of growth conditions on the optical, mechanical and electrophysical properties the lanthanum-gallium silicate group crystals
Buzanov Oleg1, Kozlova Nina2, Kozlova Anna2*, Zabelina Evgeniya2, Siminel Nikita,2 Spassky Dmitriy3,4
1OAO Fomos Materials, 119049 Moscow, Buzheninova st., 16 (Russia) 2National University of Science and Technology “MISiS”, 119049, Moscow, Leninsky pr., 4 (Russia) 3Institute of Physics, University of Tartu, Ravila 14c, 50411, Tartu, Estonia 4Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, Russia *email: [email protected]
Lanthanum – gallium tantalate La3Ta0.5Ga5.5O14 (langatate) and lanthanum – gallium silicate La3Ga5SiO14 (langasite) are the crystals with the structure of the Сa-gallogermanate. The space group of symmetry is P321. High values of piezoelectric coefficient and thermostable cuts allowed to apply the langasite for creating filters and resonators on surface and bulk acoustic waves. The drift of the piezoelectric coefficients is not observed in langatate in contrast to langasite and other piezomaterials therefore it is used for high-temperature sensors of different physical values. To use in such high temperature sensors langatate crystals are processed with different methods of machining (cutting, grinding, polishing). Currently, the electrophysical properties of langatate crystals mechanical characteristics and their dependence on the growth atmosphere have not been discussed much in the literature. Accordingly, this study is concerned with the influence of the growth atmosphere on the optical transmission spectra, mechanical and electrical properties of langatate and langasite crystals. For this study the langatate and langasite crystals were grown from iridium crucibles by the Czochralski process at Fomos-Materials, in the athmospheres of argon (Ar), argon with oxygen (Ar+O2). Oxygen concentrations in the growth atmosphere were about 2% for langasite and <1, <2, and ~2% for langatate. In a crystal point defects and their complexes influence its color and its electrical behavior, acting as color centers. Optical spectroscopy therefore represents a very sensitive tool to examine point defects. The influence of different growth atmospheres on optic transmission spectra of the crystals showed that decreasing of oxygen concentration in growth atmosphere of crystal lead to the considerable improvement of their optical characteristics [1]. The measuring method of microhardness is effective used for estimation of mechanical properties of the crystals. The microhardness of langatate crystals obtained in different growth atmospheres was studied and microhardness anisotropy was found out. Langatate measuring sensors designed to operate at high temperatures often suffer from surface degradation beneath the current carrying coating, which is applied to a polar cut. The thermal and thermal-frequency dependences of langatate electrophysical parameters in constant and alternating electric fields in the temperature range 20-500 oC were investigated. The frequency dependences of relative dielectric constant (ε11/ε0), admittance, tg δ depend on the growth atmosphere. The langatate electrophysical properties in alternating electric field were analyzed by means of impedance spectroscopy method. The equivalent circuits were constructed by using the method with allowance for the electrochemical processes of a cell “electrode-crystal-electrode”. The parameters of this electrochemical cell were determined; the input of different near-electrode processes into electrophysical properties of LGT was estimated.
References: [1] Kozlova N.S., Buzanov O.A., Zabelina E.V., Kozlova A.P., Siminel N.A., Russian Microelectronics, V.40 (2011) №8, p. 562-566
Micro-structural characterization of directionally solidified eutectic oxides
Maya Cherif1, 2, Gourav Sen2,3, Vicky Vikram Das2,Laurent Carroz1, 3, Omar Benamara4, Michel Parlier5 and Thierry Duffar*2
1 SNECMA Villaroche, Rond-point René Ravaud, 77550 Réau, France 2 SIMaP-EPM, UMR 5266 CNRS, 38402 Saint Martin d’Hères, France 3 RSA, 380 Rue Rn 85 BP 16, 38560 Jarrie, France 4ILM,UMR 5306 CNRS, 69622 Villeurbanne, France 5Onera, Chemin de la Hunière et des Joncherettes BP 80100, 91123 Palaiseau, France *email: [email protected]
These last decades, directionally solidified eutectic oxides have drawn attention due to their very good mechanical properties at high temperature. Our study focuses on the directional solidification of Al2O3-YAG-ZrO2 ternary eutectic by three different growth techniques: EFG, Bridgman and Micro-Pulling down, allowing a large range of growth conditions such as growth rate and temperature gradient. This material exhibits a complex, interconnected microstructure. The microstructure has been characterized for all grown samples by SEM and high resolution micro- tomography. The eutectic spacing, the colonies size, the phase shape and continuity have been calculated with different image processing using an open source software “Fiji”. The relevancy of the calculated parameters and the influence of the growth conditions have been investigated by statistical methods (analysis of variance, Student test...).
Towards bulk cubic silicon carbide: Growth mechanisms and related defects Rositsa Yakimova
Linkoping Inuversity, Linkoping (Sweden) email: [email protected]
Among more than 200 polytypes, cubic (3C) SiC is the only one exhibiting smaller band gap and isotropic crystal structure, respectively properties. This makes it very attractive for development of metal–oxide–semiconductor field-effect transistors, high efficiency solar cells, biocompatible medical devices or biomarkers. Furthermore, it is a perfect substrate for the growth of nitride and epitaxial graphene layers. However, 3C SiC is a metastable phase and it is very difficult to control its growth. Bulk crystal growth has not been successful until now and this material has been mainly grown on Si or hexagonal SiC substrates. In these cases a lot of defects are formed which deteriorate the grown material quality. In this talk we will summarize state of the art results showing the progress in recent understanding of growth mechanism of cubic SiC on hexagonal SiC with a flat and stepped surface (on- and off axis) aiming at developing bulk-like crystals. Growth mechanisms are different, while some common defects appear mainly related to the 3C development on hexagonal type structure. Defect formation accompanying polytype transformation and enlargement of initially nucleated domains will be elucidated by using optical microscopy, Raman spectroscopy, Photoluminescence, preferential etching and Transmission Electron Microscopy. It will be evidenced that structural evolution can be mediated and controlled by selecting substrates and specific growth conditions.
Second-phase particle migration via Temperature Gradient Zone Melting
Kerry Wang, Andrew Yeckel, and Jeffrey J. Derby*
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, U.S.A. *email: [email protected]
Crystals of compound semiconductors, such as cadmium telluride, typically exhibit populations of second-phase particles that can be deleterious to device performance. While the formation mechanisms of larger particles are not well understood, their general presence is unavoidable due to the room-temperature supersaturation of one species, caused by off-stoichiometry composition and configurational entropic effects during growth from the liquid phase. As an alternative to preventing particle formation during growth (which may not be possible), a post-growth treatment may provide higher-quality crystals. Namely, large, secondary-phase particles can be induced to move, leaving regions that contain far fewer particles. This accomplished by heating the sample to slightly above the eutectic temperature (the melting point of the second-phase particles) and applying a temperature gradient across the sample. Under such conditions, the now-liquid particle dissolves on the hot side and re-solidifies on the cool side, with a net effect of migrating toward the hotter region. This phenomenon is termed “temperature gradient zone melting,” or TGZM. Historically, its discovery was motivated by the experience of Arctic explorers, who found that newly formed sea ice was not potable due to brine inclusions. However, after 2-3 years of exposure to sunlight, this sea ice could be used for drinking water. In the aging process, brine inclusions migrate to the surface by diurnal heating, thus purifying the ice. Tiller in 1963 devised the first approximate mathematical model to describe inclusion migration via TGZM. In this presentation, we present the formulation of mathematical models for particle migration via TGZM. We demonstrate that an approximate analytical solution to this model in one spatial dimension well describes the general behavior of particle migration. The analytical solution shows that steady-state migration is not possible, and that, under a constant thermal gradient, the particle velocity and size increase continually with time. Experimental observations are consistent with these predictions. We also describe the implementation of a moving-boundary, finite-element method that solves the model equations with no simplifying assumptions about mechanistic interactions. Initial results provide excellent predictions of particle migration in cadmium telluride.
Figure 1. The model for particle migration in a thermal gradient is shown on the left. Computed results for a spherical tellurium particle migrating through solid cadmium telluride are displayed on the right. ______This research was supported in part by the U.S. Department of Homeland Security, 2012-DN- 077-ARI066-02; no official endorsement should be inferred.
Effects of Annealing Treatments on Microstructures of Aluminum Nitride Buffer Layer Grown by MOVPE
Kuwano Noriyuki*1, Kaur Jesbains1, Fukuda Junya2, Soejima Yohei2, Mitsuhara Masatoshi3, Suzuki Shuhei4, Miyake Hideto5, Hiramatsu Kazumasa4 and Fukuyama Hiroyuki6)
1MJIIT, Universiti Teknologi Malaysia, Jalan Sultan Yahya Petra, 54100 Kuala Lumpur (Malaysia) 2Dept. Appl. Sci. Electr. Mater., Kyushu University, Kasuga Fukuoka 816-8580 (Japan) 3Dept. Eng. Sci. Electr. Mater., Kyushu University, Kasuga Fukuoka 816-8580 (Japan) 4 Dept. Elect. Electr. Eng., Mie University, 1577 Kurimamachiya-cho Tsu city, Mie 514-8507 (Japan) 5Grad. Sch. Regional Innovation Studies, Mie University, 1577 Kurimamachiya-cho Tsu city, Mie 514-8507 (Japan) 6 IMRAM, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan) *[email protected]
In order to grow a high quality aluminum nitride (AlN) thin layer, it is essential to prepare good quality AlN templates for overgrowth. In the present work, the microstructure in AlN buffer layers fabricated on a sapphire substrate was characterized by electron microscopy, and the changes in defect structure with the heat-treatment for the sapphire substrate and the deposited AlN buffer layer were investigated to seek the growth process for high quality AlN. AlN was deposited on a (0001) sapphire substrate by MOVPE method with TMA and NH3. First, the sapphire substrate was annealing for surface cleaning under H2 atmosphere at Tcl and then an AlN buffer layer about 100 nm thick was deposited at about 1200oC. Thereafter, an AlN layer was overgrown on the buffer layer at 1500oC to be about 1μm in thickness. Some templates of the buffer layer were annealed at Tan under the atmosphere of (CO + N2) before deposition of AlN layer. Specimens for SEM and TEM observation were made using a focused ion beam (FIB) mill and an Ar ion mill. Observation was conducted with JEM-2000EX, JEM-ARM and Ultra55. EBSD analysis, AFM observation and X-ray rocking curve (XRC) measurements were also performed. It was found that XRC of hkl=102 starts to increase in line width (FWHM) at 1250oC and is split to two peaks above 1300oC. These changes in XRC are due to formation of twisting domains. TEM observation confirmed that there are two types of twisting domains. Domains about 50-80 nm in diameter arranged alternately in a regular way, and those of an oval shape about 0.5 ×1.5 μm, composed with those of the former type. The results suggest that the formation of twisting domains have two different origins; the (0001) surface and the step walls of sapphire substrate, respectively. o When Tcl is lower than 1200 C, twisting domains do not appear but inversion-regions are formed near the interface of AlN/sapphire. Columnar inversion domains are developed up to the top surface of AlN layer. The origin for inversion region is not yet clarified but oxygen atoms are thought to play important role in growth process including the formation of Al(N,O). There are several types of defects in AlN layer to be taken into account: threading dislocations, twisting domains and inversion domains as well as surface morphology. Fortunately stacking faults are not formed in the present AlN layers. It is not easy to decrease these lattice defects at one time under a single condition of growth process: For example, when the growth temperature is raised in order to decrease the density of dislocations, inversion domains are developed and the surface becomes rough in morphology. In the course of investigation of process-optimization, it was found that a high quality AlN layer was successfully grown on an AlN buffer layer after annealing at high temperature. TEM observation confirmed that by annealing at 1500oC for 2 hr, the inversion regions in an AlN buffer layer have changed to be domains of turned cone shape, and at 1550oC the inversion domains coalesce with each other, leaving a single inversion domain boundary that runs parallel to the top surface. The results show that annealing is a very effective treatment for microstructure control even for semiconductor crystals.
The role of screw dislocations in habit modification of KDP by impurity
Xiaojun Lai 1, Kevin Roberts 1 and Helmut Klapper 2 1 Institute of Particle Science and Engineering and Institute of Process Research and Development, School of Chemical and Process Engineering, University of Leeds, LS2 9JT, UK 2 Institute of Crystallography, RWTH Aachen University, D-52056 Aachen, Germany [email protected]
Crystal habit modification by impurities is of fundamental challenge concerning with industrial crystallisation processes. In the complicated process systems, some chemical components often serve as impurities resulting in undesired crystal morphologies. On the other hand, some research has demonstrated optimizing crystal shape by employing habit modifying additives to control the relative growth rates of the crystal surfaces, such as using attachment energy, to predict the growth rates of the crystal habit faces. However, only very few systems have, as yet, been fully studied. The problems concerning the physical and chemical processes associated with such habit modifying agents remain largely unknown at this time, e.g. the impurity structure and bonding in the crystal, and growth mechanisms of crystal habit faces with presence of the impurities.
In this research potassium dihydrogen phosphate (KH2PO4, KDP) is investigated as a representative system. Large single crystals of KDP were grown by solution cooling in presence of Cr3+ or Mn3+. The crystals are elongated on [001] direction and (100) prismatic faces became tapering through the impurity incorporation. The impurity structure as a form of transition metal complex and the chemistry associated with its incorporation, have been characterized by x-ray spectroscopy/diffraction techniques in our previous study. [2] X-ray topography is used to investigate the crystal defects in order for the mechanism of the crystal tapering. Screw dislocations with the Burger’s vectors are characterized with respect to their types and line directions. The growth history in the images of x-ray topographs shows that the tapering shape of (100) faces was formed during the fast growth of the (101) faces; this tapering angle was reduced and finally disappeared when the relative growth rate of the (101) slowed down. The x-ray topography provides the evidence of dislocations undergoing their redistribution from the (101) growth sector to the (100) sectors due to the elongated shape derived. Therefore, the growth kinetics of (101) faces switches from the spiral growth step to the 2-d surface birth & spread. The step growing directions and rates determined by the screw dislocations on the (100) and (101) faces play the critical role in growth layers’ coverage at the boundary between the growth faces or sectors, and hence determine the formation of the tapering morphology of KDP.
References: [1] Hammond R. B., et al, CrystEngComm, 2011, 13, 4935 [2] Lan Z., Lai X., et al, Cryst. Growth Des. 2014, 14, 6084
The role of twin boundaries in growth of natural and Fe-doped SnO2 crystals
Sara Tominc*1, 2, Nina Daneu1, Aleksander Rečnik1
1Jožef Stefan Institute, Jamova 39, Ljubljana (Slovenia) 2Jožef Stefan International Postgraduate School, Jamova 39, Ljubljana (Slovenia) *email: [email protected]
According to a number of studies, cassiterite (SnO2) is an attractive material for a wide range of applications such as solid-state gas sensors, surge arrestors (varistors), transparent conductors, solar cells, catalysts and others [1]. In most of these applications, it is essential to control the crystal growth and evolution of the microstructure. One of the main future objectives involves chemically- induced twinning that offers a wide range of possibilities to grow complex branched architectures with tunable physical properties. The main challenge of this work will be to determine whether the cause of twinning in SnO2 is topotaxial growth on still unknown precursor material, or is the source tropochemical. The principle will be verified by reproducing the twinning under constrained laboratory conditions. To understand the twinning mechanism we first investigated natural twins of cassiterite from Viloco mine near La Paz in Bolivia. Samples for transmission electron microscopy (TEM) studies were prepared from natural twins along low index zone axes, [010] and [101]. Energy dispersive spectroscopy (EDS) analysis confirmed that the twin boundaries are genetically related to the presence of Fe. The twin boundary is characterized by numerous oriented Fe-rich inclusions, located at the {101} twin boundary and also in bulk cassiterite. Using selected area electron diffraction (SAED) analysis and Fourier transforms (FFT) from HRTEM images recorded along the twin boundary, we confirmed that both symmetry and d-spacings of these precipitates best correspond to magnetite (Fe3O4). To reproduce twinning in laboratory, we prepared SnO2-based ceramics with the addition of 1 mol % of iron oxide (Fe2O3). The samples were sintered at 1300 °C for 5 hours and thermally etched at 1250 °C for 15 minutes to reveal the microstructure. Polished cross-sections of the samples were characterized using optical and scanning electron microscopy (SEM). Further TEM investigations will be applied to confirm whether the Fe-rich additives in fact trigger the formation of twin boundaries in SnO2.
Figure 1: (a) Low magnification TEM image of (natural cassiterite twin with corresponding experimental diffraction pattern. (b) SnO2 ceramics doped with 1 mol % Fe2O3 displaying twinned crystals.
References: [1] Parra R., Ramajo L.A., Góes M.S., Varela J.A., Castro M.S.., Mat. Res. Bull. 43 (2008) 3202-3211.
POSTER
S09-P03 Study of charge compensating defects in BaF2:YbF3 crystals using dielectric relaxation
Irina Nicoara1*, Marius Stef1, Octavian Bunoiu 1
1West University of Timisoara, Dept. of Physics, Bd. V. Parvan nr 4, Timisoara, Romania *email: [email protected]
Barium fluoride crystal finds applications as a transmitting window over a wide wavelength range, as a fast scintillator involving emission at 195 nm and 220 nm and doped with rare-earth 3+ (RE) ions as laser material. The RE -ions usually occupy a cation substitutional position in BaF2 lattice and charge compensation is required to maintain the electrical neutrality of the system. The extra positive charge is compensated by an interstitial fluorine ion. This indeed leads to a complex site structure including so-called isolated ions, pairs (or dimers) of adjacent rare-earth ions, clusters, etc., depending on the nature of the substituted cation, of the RE dopant and of the dopant concentration. In order to understand the spectroscopic properties of the crystals it is important to know the type of the charge compensating defects that are format. Local compensation by pairing of Yb3+ ions with interstitial F– ions create electric dipoles whose relaxation are observed as dielectric absorption. Temperature and frequency dependence of the complex dielectric constant (the dielectric spectrum) gives information about the impurity- defect aggregates [1, 2]. The goal of this work is to study the dielectric spectra of the YbF3-doped BaF2 crystals in order to obtain information about the impurity-defect formation in these crystals. Various concentrations YbF3 -doped BaF2 (0.05, 0.1, 0.2 mol% YbF3) crystals have been grown using the conventional Bridgman method. Transparent colorless crystals of about 10 mm in diameter over 5-6 cm long were obtained in graphite crucible in vacuum (~ 10-1 Pa) using a shaped graphite furnace [3], the pulling rate was 4mm/h. The optical absorption spectra reveal the existence of both Yb2+ and Yb3+ ions. The dielectric measurements were performed using a RLC Meter ZM 2355, over the temperature range 150–300 K, at nine audio-frequencies 1–100 kHz. The real part of the dielectric constant, ε1, has been calculated from the measured capacitance. The ε2 has been then calculated from D= ε2/ ε1 (D = tan δ is the dielectric loss). The relaxation parameters (the activation energy for dipole reorientation and relaxation time constant) have been calculated in order to characterize the observed relaxations. We assign the observed relaxation to trigonal type (C3v) centres. The number of the dipoles, ND , that contribute to the dielectric relaxation have been determined from the dielectric spectra; the correlation between ND and the optical spectra has been also discussed. A comparison of dielectric spectra of CaF2:YbF3 and BaF2:YbF3 crystals is also given.
Acknowledgment. This work was supported by the Romanian Ministry of Education and Research, grant ELICRYS, Contract nr.13/30.06.2014 in the frame of Capacities/RO-CERN (ELI- NP) Program.
References: [1] J. Fontanella and D. J. Treacy, J. Chem. Phys. 72 (1980) 2235, [2] I. Nicoara and M. Stef, Eur. Phys. J. B (2012) 85:180 DOI: 10.1140/epjb/e2012-20914-8 [3] D. Nicoara and I. Nicoara, Mater. Sci. Eng. A 102 (1988) L1.
S09-P04 Some optical properties of YbF3 doped BaF2 crystals
Irina Nicoara1*, Marius Stef1, OctavianBunoiu 1
1West University of Timisoara, Dept. of Physics, Bd. V. Parvan nr 4, Timisoara, Romania *email: [email protected]
In the last time the interest in rare-earth (RE)-doped MeF2 (Me= Ca, Sr, Ba) crystals used as laser material is still growing due to the well known good optical characteristics of the fluorite host. The Ytterbium ions are most easily stabilized as trivalent ions in MeF2 crystals, the divalent state has certain distinct advantages for laser applications [1, 2]. The properties of low concentration YbF3 doped BaF2 crystals have been less investigated than the other RE doped BaF2 crystals [3]. In this work we report the growth and some optical properties of YbF3- doped BaF2 crystals with high concentration of divalent Yb ions obtained without any other treatment. Ba1-xYbx F2-x (x = 0.0005, 0.001 and 0.002) crystals have been grown using the conventional Bridgman technique. Transparent colorless crystals of about 10 mm in diameter over 5-6 cm long were obtained in graphite crucible in vacuum (~ 10-1 Pa) using a shaped graphite furnace [4]; the pulling rate was 4 mm/h. The goal of this work is to study the optical absorbtion spectra of low YbF3 concentration doped BaF2 crystals in order to obtain information about the impurity-defects formation. It is known that the optical properties of the crystals depend on the Yb2+ , Yb,3+ and F- ions positions in the lattice. The Yb3+ ions substitute for Ba2+ ions and need charge compensation obtained by an interstitial fluoride ion located in various positions giving rise to a rich multisite structure, which leads to broad absorption bands. The Yb2+ ions substitute for Ba2+ ions, do not need charge compensation and posses cubic symmetry. The optical absorption spectra of our crystals reveal the existence of both Yb2+ (in the near-UV) and Yb3+ ions (in near-IR domain). 2 These spectra are characterized by a very broad band in near-IR domain, corresponding to the F7/2 2 3+ - F5/2 transitions of the Yb ions [3, 5]. Unlike the spectra of high YbF3 concentration crystals [16], in the case of our low concentration YbF3 doped BaF3 crystals three principal maxima (928 , 968 and 974 nm) and four weak peaks have been observed. In each case the dominant peak is at 968 nm. Taking into account our dielectric relaxation measuremets we assign this peak to C3v centre, with the charge compensating interstitial F- ion occupying a next-nearest neighbor position in a 3+ [111] direction from the Yb ion. As the YbF3 concentration inceases the intensity of the second peak at 974 nm (assigned to clusters, CR) [3] increases. The intensity ratio between these two peaks (CR/C3v) increases as the concentration increases: 0.5, 0.7 and 1.1.The peak at 928 nm corresponds to the centre with cubic (Oh ) symmetry, and the small peaks are associated with other defects where the charge compensation is provided, probably, by oxygen impurities or/and to marginal population of Yb3+ ions in other symmetries.
Acknowledgment. This work was supported by the Romanian Ministry of Education and Research, grant ELICRYS, Contract nr.13/30.06.2014 in the frame of Capacities/RO-CERN (ELI- NP) program.
References: [1] A. A. Kaplyanskii et al., Opt. Spectrosc. 41 (1976) 615, [2] B. Moine, B. Courtois and C. Pedrini J. Physique 50 (1989) 2105 [3] D. Camy, J. Doualan, A. Benayad, M von Edlinger, V. Menard and R. Moncorge, Appl. Phys. B 89 (2007) 539 [4] D. Nicoara and I. Nicoara, Mater. Sci. Eng. A 102 (1988) L1 [5] J. Kirton and S.D. McLaughlan, Phys. Rev. 155 (1967) 279.
S09-P05 Interplay mechanism of secondary phase particles and the extended dislocations in CdZnTe crystals Yadong Xu1, 2*, Yihui He1, Ningbo Jia1, Rongrong Guo1, Yaxu Gu1, Yuecun Wang1, Wanqi Jie1 1State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China 2Laboratory of Solid State Microstructures, Nanjing University, 210093, China *email: [email protected] The presence of SP particles often markedly affects the optical and electronic properties of the bulk crystals as well as the surface perfection of epitaxial substrates. They appear not only in II-VI (e.g., CdTe, ZnSe), III-V (e.g., GaN), and IV-VI (e.g., SiC) compounds, but also in oxides and fluorides. CdZnTe (CZT) crystals have been studied intensively due to their potential applications in X/γ-ray detection and the growth of HgCdTe epilayers. However, localized regions with SP particles (inclusions/precipitates) and induced dislocations are usually generated inevitably in as-grown or post- growth annealed CZT crystals [1, 2], which are known to be detrimental to the charge collection for CZT detector, simultaneously to degrade the epilayers crystallization. Therefore, it is meaningful to study the relationship between SP particles and induced dislocations, in order to orient towards material with either better performance or lower concentration defects. To manifest the interplay mechanism between dislocations and Te-SP particles, dislocation arrangement surrounding Te-SP in CZT crystals was investigated after isothermal and thermal gradient annealing under specific atmospheres in this work. Employing defect-selective etching techniques, the distributions of Te-rich SP particles and dislocations on CZT {111)}Te surfaces were observed using correlative reflected-light/IR transmission and scanning electron microscopy (SEM). In addition, the extended defects of local areas were identified by transmission electron microscopy (TEM) and cathodoluminescence (CL) microscopy. Two possible models for growth and multiplication of dislocation clusters are proposed on the basis of dissociation-diffusion and thermomigration-deformation, respectively.
Figure 1. (a) SEM image of as-grown CZT {111}Te face after etching by Everson solution. (b) ‘Radial-shaped’ etch pits rosette surrounding a Te-SP (c) Typical optical image of CZT {111}Te by defect-selective etching after 650 °C annealing. (b) ‘Star-shaped’ dislocation cluster. Our investigations demonstrated that Te-rich SP particles are more efficiently eliminated under thermal gradient annealing than that under isothermal annealing. However, ‘radial-shaped’ dislocation rosettes and ‘star-shaped’ dislocation clusters are observed more frequently after annealing under Cd/Zn atmosphere, as seen in Figures 1. The driving forces which lead to the generation and multiplication of the dislocations rosette have been discussed. During the isothermal annealing at Cd/Zn overpressure, Te-SP dissociation dominates the volume variation, which results in the dislocations glide and climb systems activate, simultaneously with the diffusion of Tei. Then growth and multiplication of the dislocations are enhanced by the thermal stress, which is attributed to the exothermic reaction between Cd/Zn and Tei. A proposed model is demonstrated in Figures 2, which shows the evolution of Te-SP and the surrounding etch pits rosette on {111}Te. However, for thermal gradient annealing, Te-SP migration towards the high temperature side is superior to the dissociation. The recrystallization quality is related with the drift velocity of Te droplets. Lattice deformation in CZT near surface region is accompanied by the dislocation multiplication due to the severe misfit stress.
Figure 2. Diagram of the evolution of Te-SP and the surrounding etch pits rosette on {111}Te. References: [1] Yadong Xu, Yihui He, Tao Wang, et al., Investigation of Te inclusion induced glides and the corresponding dislocations in CdZnTe crystal. Crystengcomm, 2012. 14(2): 417-420. [2] Yihui He, Wanqi Jie, Yadong Xu, et al., Matrix-controlled morphology evolution of Te inclusions in CdZnTe single crystal. Scripta Materialia, 2012. 67(1): 5-8.
S09-P06 Oxygen precipitation behavior in heavily arsenic doped silicon crystals
Stephan Haringer1, Daniela Gambaro2, Maria Porrini1*
1MEMC Electronic Materials SpA, via Nazionale 59, 39012 Merano (Italy) 2 MEMC Electronic Materials SpA, viale Gherzi 31, 28100 Novara (Italy) *email: [email protected]
The behavior of oxygen precipitation in silicon has been studied for decades, and there is a vast literature in this field [1]; however, most of the studies have concerned either lightly doped wafers or heavily boron doped wafers. Very little information is available in the case of heavily doped N- type silicon wafers, and especially for the large diameters and high concentration levels that are becoming more and more requested nowadays by the expanding market of discrete devices. Moreover, the few available papers examine commercial wafers, whose position in the crystal is not specified, and for which no information on the previous thermal history is available [2, 3]. Purpose of this work is to contribute to the understanding of oxygen precipitation behavior in large diameter, heavily arsenic doped silicon crystals grown with the Czochralski method. Silicon crystals containing different levels of arsenic concentration and oxygen content were grown, and samples were taken at various positions along the crystal, to study the influence of three main factors, i.e. the initial oxygen content, the dopant concentration and the thermal history, on the nucleation of oxygen precipitates during crystal growth and cooling in the puller. The crystal thermal history was reconstructed by means of computer modeling, simulating the temperature distribution in the crystal at several growth stages. The oxygen precipitation was characterized after a thermal cycle of 4 h at 800°C for nuclei stabilization + 16 h at 1000°C for nuclei growth. Oxygen precipitates (BMD) were counted under microscope on the cleaved sample surface after preferential etching. Lightly doped silicon samples were also included, as reference. Our results show that also in heavily arsenic doped silicon the oxygen precipitation is a strong function of the initial oxygen concentration, similar to what has been observed for lightly doped silicon. In addition, a precipitation retardation effect is observed in the arsenic doped samples when the dopant concentration is higher than 1.7x1019 cm-3 compared to lightly doped samples with the same initial oxygen content and crystal thermal history. Finally, a long permanence time of the crystal in the temperature range between 450°C and 750°C enhances the oxygen precipitation, showing that this is an effective temperature range for oxygen precipitation nucleation in heavily arsenic doped silicon.
References: [1] see for example: A. Borghesi, B. Pivac, A. Sassella, A. Stella, Journal of Applied Physics, 77(1995) 4169 – 4244 [2] W. Sugimura, T. Ono, S. Umeno, M. Hourai, K. Sueoka, ECS Transaction 2(2) (2006) 95 – 107 [3] Y. Zhao, D. Li, X. Ma, D. Yang, J. Phys.: Condens. Matter 16, (2004) 1539 – 1545
S09-P07 Blocks and Residual Stresses in Shaped Sapphire Single Crystals Krymov V.M., Nosov Yu.G. , Bakholdin S.I., Maslov V.N., Shul’pina I.L., Nikolaev V.I. Ioffe Institute, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia e-mail: [email protected] The single-crystal rods and tubes grown from the melt by the Stepanov (EFG) method are widely applied in technology. In some cases of usage, such as seeds for bulk crystals growth or for the production of gas- discharge lamps, the crystals without blocks and residual stresses are required. The influence of seed crystallographic orientation, conditions of a seeding and thermal stresses on the development of blocks and residual stresses in the crystals of various forms has been studied. Sapphire rods of circular (diameter of 8, 12 and 23 mm) and square (8х8) mm cross sections and tubes (10x8), (27x10) and (16х9) mm were grown. The block structure of the grown crystals has been studied by the polarization-optical method and X-ray diffraction topography. Сrystallographic orientation. It is shown that in most cases, at growth of sapphire rod in the c direction - along the optical axis [0001], the block - mosaic structure is formed . The initial part of such crystal contains separate large blocks. In the process of a crystal growth the ring-shaped development of block structure from a crystal surface to the center with reduction of the block sizes is observed. It has been found that when rods are being grown in the a direction [2 1 1 0], the structural perfection of crystals is higher and local near-surface blocks are formed only rarely. For the tubular form crystals grown in the a direction the strong development of blocks in the areas of the presence of two (0001) faces on a lateral crystal surface is observed. The formation of block structure in cross section and along the length in c direction tubes is similar to the rods of the same orientation. Seeding. Block-free single crystal rods of both orientations with the diameter up to 20 mm can be obtained using a block-free seed and with the exact thermal mode of a seeding. However when the crystal diameter exceeds 20 mm, the thermal stresses are increased and blocks nucleation in c crystals is possible even when a block-free seed is used and thermal seeding conditions are fulfilled. Thermal stresses. The residual stresses in cross sections of the sapphire [0001] crystals have been studied using the optical konoskopiya method. Both the rod of circular section 23 mm in diameter and the tube 27x10 mm have been investigated. The difference of stresses (σφ-σr) in rod is minimum in the central part and is increased to its periphery. The maximum tensile stresses act at a rod surface. Their value doesn’t exceed 20 MPa. The difference (σφ-σr) for tubular single crystals reaches the maximum values 15-20 MPa at external and internal surfaces. It has been shown that the tensile stresses act at the external surface of tube whereas the compression stresses act at its internal surface. The comparison of the measured residual stresses distribution and calculated thermal stresses allowed to come to the conclusion that imperfect structure and residual stresses are caused by plastic deformation of the grown crystal in a very restricted high-temperature area (height about 1 mm) from the crystallization front.
References: [1] Krymov V.M., Nosov Yu.G., Bakholdin S.I, Maslov V.N., Shul’pina I.L., Crystallography Reports, Vol. 60, (2015), p. 377. [2] Krymov V.M., Nosov Yu.G., Bakholdin S.I, Galaktionov E.V., Maslov V.N., Tropp E.A., Physics of the Solid State, Vol. 57, (2015), p.746.
S09-P08 Strain Energy Analysis of Screw Dislocations in 4H-SiC by Molecular Dynamics
Takahiro Kawamura*1, Mitsutoshi Mizutani1, Yasuyuki Suzuki1, Yoshihiro Kangawa2, Koichi Kakimoto2
1Graduate School of Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu, 514-8507 (Japan) 2Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka 816-8580 (Japan) *email: [email protected]
Silicon carbide (SiC) is an attractive wide-gap semiconductor for fabricating high-power and energy-conserving devices. It is known that crystal defects such as threading screw dislocation, threading edge dislocation, stacking fault, etc. deteriorate the device performance [1]. To overcome the problems, we need to understand the defect structure in detail. In this study, we analyzed strain energy of screw dislocations in 4H-SiC using molecular dynamics simulation. Simulation cell was composed of 614400 atoms and its size was 494330 (a-, m-, and c-axes) nm3. The periodic boundary condition was applied along the c-axis direction. Atoms on the edge of the simulation cell in the a- and m-axis directions were fixed. A dislocation core was set at the center of the a-m plane and the burgers vector was parallel to the c-axis. We simulated screw dislocations with Burgers vector (BV) = 1c, 3/4c, 1/2c, and 1/4c, where “c” is the thickness of four atomic layers of SiC. Strain energy of each atom (Estrain) was defined by Estrain = Escrew Eperfect, where Estrain is the potential energy of the simulation model including a screw dislocation and Eperfect is the potential energy of perfect crystal. The simulation time was 10 psec (10000 step) and the temperature was set to 0 K. We used Brenner potential [2,3] to calculate interatomic forces. Figure 1 shows the map of strain energy of each atom when the BV was 1/2c. We can see that there was large strain at the dislocation core and the plane defect. The plane defect was observed when the BV was 3/4c, 1/2c, and 1/4c. Figure 2 shows the total strain energy within a radius r from the dislocation core. From the inset, it was found that the total strain energy caused by the dislocation core increased with the BV. The values of 1c converged with increasing the radius. On the other hand, in the large radius region, the values of 3/4c, 1/2c, and 1/4c were proportional to the radius because of the contribution of the plane defect. Comparing the slope of the three graphs (3/4c, 1/2c, and 1/4c), the slope of 1/2c was the smallest and those of 3/4c and 1/4c were almost the same. This indicates that when the BV was 1/2c, the strain energy per unit area caused by the plane defect was the smallest among the three cases.
Figure 1. Strain energy map Figure 2. Strain energy within a radius from the (Burgers vector = 1/2c) dislocation core. The inset is the magnification in the small radius region. References: [1] H. Fujiwara et al., Appl. Phys. Lett. 101 (2012) 042104. [2] D. W. Brenner, Phys. Rev. B 42 (1990) 9458. [3] A. J. Dyson and P. V. Smith, Molecular Physics 96 (1999) 1491.
S09-P09 STUDY OF DEFECT FORMATION IN KDP CRYSTALS UNDER HIGH SUPERSATURATION Baskakova Svetlana*, Voloshin Alexey Shubnikov Institute of Crystallography of RAS, Moscow, Russia *e-mail: [email protected]
During crystal growth from aqueous solution the defect formation is determined mainly by processes occurring on the growing face. If the mechanism of crystal growth is changed from the spiral one to the two- dimensional (2D) nucleation it is expected the change of mechanism of defect formation. Growth of inorganic crystals from aqueous solutions at low supersaturation has been studied by various authors in sufficient detail. But due to the difficulties in crystal growth at high supersaturation in the water-salt systems, these issues at 2D nucleation have never been studied. There are several articles, which describe X-ray topography investigation of KDP crystals grown under high velocity [1-3]. But supersaturation in these experiments was not enough for realization of 2D nucleation mechanism. In addition, there are a couple of articles on KDP crystal growth at supersaturation 25 - 60% [4-5] but X-ray topographic studies were not conducted there. Thus, the data about defect formation under 2D nucleation at high supersaturation are very poor and did not allow one to make the complete picture. Therefore, this work is a study of the main types of defects and the mechanisms of their formation in crystals grown from aqueous solutions at high supersaturation, when the growth is driven by 2D nucleation. KDP crystal was taken as a model object. Calculations of the KDP crystal growth kinetic curves show that domination of the 2D nucleation over the dislocation spiral growth might be achieved at supersaturation higher than 20%. A series of KDP crystals was grown at the supersaturation 25% and studied by X-ray topography. There are zonality of morphological type and sub-sectorial boundaries, indicating the partial realization of spiral growth. At the supersaturation 35% and 40% dislocation beams and sectorial boundaries are visible on the performed topographs. Chaotic set of strongly curved lines is seen in the prism sectors of the crystal grown at 40%. To study the zonal inhomogeneity of KDP crystals under high supersaturation, the crystal was obtained with the change of supersaturation from 35% to 38% during the growth (Figure 2, №3). The stripe continuous at all sector boundaries was found on the crystal topograph, this is typical for crystals grown by 2D nucleation mechanism. Finally, a crystal was grown at the supersaturation 60% (Figure 3). On the crystal topograph there are not seen zonal inhomogeneity, sectorial borders are greatly weakened, dislocation bunches are completely absent in the sector of the prism, a small bunch is observed in the sector of the pyramid. The obtained results generally confirm the difference in the mechanisms of zonal inhomogeneity formation under the spiral growth and 2D nucleation. But spiral growth at the supersaturation 40% still appears quite noticeably affecting on the overall pattern of impurity distribution. However, the lack of zonal inhomogeneity and reduction of the number of dislocations bunches at 60%, apparently, indicates the predominance of the 2D nucleation mechanism over the spiral growth. This study was conducted with support from the Russian Foundation for Basic Research (grant No. 13-02-12163-ofi- m). References: [1] Zaitseva N.P., Smolski I.L., Rashkovich L.N. Crystallography 1 (1991) 36 [2] Smolski I.L., Zaitseva N.P. Crystal Growth, Volume 19. [3] Zaitseva N.P., De Yoreo, Dehaven et al., Journal of Crystal Growth 180 (1997) 255 [4] Zaitseva N.P., Rashkovich L.N., Bogatyreva S.V. Journal of Crystal Growth 148 (1995) 276. [5] Zaitseva N., Carman L., Smolski I., Torres R., Yan M. Journal of Crystal Growth 210 (1999) 512–524
S09-P10 Czochralski growth and characterization of rare earth-doped Gd3(Al,Ga)5O12 crystals
Ryba-Romanowski Witold *1, Komar Jarosław 1, Solarz Piotr 1, Jeżowski Andrzej1, Głowacki Michał 2, Berkowski Marek 2
1Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Okolna 2, 50-422 Wrocław, Poland 2Institute of Physics, Polish Academy of Sciences, Al. Lotników, 32/46, 02- 668, Warsaw, Poland *[email protected]
Among a large family of substituted garnets employed as hosts for luminescent rare earth ions 3+ the Gd3(Al,Ga)5O12 system is the newest one. Originally proposed for the design of Ce -doped scintillating material [1], it is able to accommodate other rare earth ions offering thereby a potential for developing new phosphors and laser materials. In the present work we consider peculiarities of point defects consisting of intentionally incorporated impurities or unintentional colour centres and their effect on macroscopic features of this disordered system. Solid solution crystals with nominal 3+ 3+ 3+ 3+ 3+ stoichiometry Gd3Al2.5Ga2.5O12 doped with Sm , Dy , Ho , Er and Yb were grown by the Czochralski method using a Malvern MSR4 puller with an automatic diameter control based on weighting the crucible. Starting oxides were dried at 1000 C for 4 hours before weighting. Powders in appropriate molar ratios were mixed together and then pressed into cylindrical pellets under pressure of 200 kPa and calcinated at 1350 C for 6 hours before melting in crucible. Single crystals were grown under nitrogen atmosphere on <111> oriented seeds with a pulling rate of 2.5 mm/h and a speed of rotation 20 rpm. Transparent crystals with 20 mm of the diameter and 60 mm in length were grown with a convex crystal melt interface from inductively heated iridium crucible of 40 mm in diameter. Recorded optical absorption spectra revealed that the intensity and spectral characteristics of colour centre absorption in the UV region, close to the UV absorption edge of the host, are affected by the type of incorporated rare earth ions and their concentration. On the other hand, spectral characteristics of stable colour centres induced by an intense UV irradiation of crystals depend weakly on the rare earth admixture. Low temperature optical spectra revealed that widths of spectral lines related to transitions between individual crystal field levels of rare earth ions are larger by a factor of four roughly, as compared to those encountered in ordered lattice of yttrium aluminum garnet. Also, low temperature optical spectra indicate that Sm3+ ions in this host occupy at least two different types of sites but much smaller Ho3+ and Yb3+ ions seem to be located preferentially in identical sites. Thermal conductivity of crystals doped with holmium or ytterbium, close to 7.9 W/mK at 300K, increases to 32 W/mK at 77 K and next, at lower temperature becomes anomalously affected by concentration of incorporated ions. Further examination of the systems under study is in progress to elucidate this puzzling observation.
References: [1]. K. Kamada, T. Yanagida, T. Endo, K. Tsutumi, Y. Usuki, M. Nikl, Y. Fujimoto, A. Fukabori, A. Yoshikawa, J. Crystal Growth, 351 (2012) 88-90
S09-P11 Nonstoichiometry and luminescent properties of ZnSe crystals grown from the melt at high pressures
Khan Tran1, Elena Mozhevitina1, Andrew Khomyakov1, Roman Avetisov*1, Albert Davydov2, Vladimir Chegnov2, Vladimir Antonov2, Svetlana Kobeleva3, Nikolai Zhavoronkov2, Igor Avetissov1
1D.Mendeleyev University of Chemical Technology of Russia, Miusskaya pl.9, Moscow (Russia) 2 Research Institute of Material Science and Technology, Proezd 4806, build.2, Zelenograd Moscow (Russia) 3 National University of Science and Technology, Leninsky prospect,4,Moscow (Russia) *email: [email protected]
AIIBVI single crystals have a number of unique properties which significantly depend on nano- scale defect type and concentration. Native point defects generating as a result of deviation from stoichiometric composition influence on luminescence, conductivity, and other structure sensitive properties similar to dopants. ZnSe 50 mm diameter crystals have been grown from the melt at 100 at argon pressure in graphite and glassy carbon crucibles. 3D impurities concentration and nonstoichiometry mapping in the grown crystals (Fig.1) have been fulfilled by ICP-MS and «extraction» techniques [1], correspondingly. Depending on the growth conditions and crucible material the crystal had overstoichiometric (excess) Se concentration which was in several orders less than the concentration at the homogeneity limits. We established the dependence of Se excess concentration on temperature and Se partial pressure within the homogeneity limits at Ss-ZnSeV bivariant equilibrium. The processing of the experimental data on the Se solubility in nonstoichiometric s-ZnSe (zinc blend) showed that in the framework of the quasi-chemical theory of defect generation the data have been adequately described, considering the generation of clusters (associates) based on electrically neutral vacancies in zinc sublattice followed by exothermic reactions. The research was supported by the Russian Science Foundation grant N 15-13-10028
Figure 1. ZnSe crystal grown by from the melt at PAr=100 atm in a graphite crucible
References: [1] Avetissov I., Mozhevitina E., Khomyakov A., Tran Khanh, Cryst. Res. Technol. 50 (2015) N 1, 93–100
S09-P12 Nonstoichiometry and luminescent properties of tris(8-hydroxyquinoline)aluminum crystals
Igor Avetissov, Alina Akkuzina, Roman Avetisov*, Andrew Khomyakov, Elena Mozhevitina,
D.Mendeleyev University of Chemical Technology of Russia, Miusskaya pl.9, Moscow (Russia) *email: [email protected]
The nonstoichiometry phenomenon is well known for inorganic crystals. The crystal nonstoichiometry results from general thermodynamic laws at T>0 K. But in the case of organic crystals it has been thought the nonstoichiometry is not valid due to a molecule structure of organic crystals. In the research we have studied the crystals behavior of tris-(8-hydroxyquinoline)aluminum (III) (Alq3) during powder heat treatment and crystal growth at controlled ligand 8- hydroxyquinoline (8-Hq) vapor (P8-Hq). Alq3 is a known organic phosphor for OLED devices. The scheme of Alq3 polymorphic transitions vs temperature has been established in [1,2]. We established the dependence of photoluminescence (PL) and crystal structure parameters of β-Alq3 change vs P8-Hq at a fixed temperature. It has been shown that P8-Hq increase results to: a) reduction of intensity at a fixed annealing (crystal growth) temperature; b) changing the temperatures of polymorphic transitions and melting; c) hypsochromic shift of PL maximum from 517 to 504-508 nm (at Tann=580 K). All changes were reversible, indicating the thermodynamic nature of the observed effects. We explained the effects by the formation of a thermodynamically equilibrium crystal structure, which depending on P8-Hq resulted to the change of Al atom number at a constant amount of ligands in the crystal structure. The suggestion was proved by XRD analysis of the crystal lattice parameters. We found the correlation between the cell volume vs P8-Hq, which indicated Al- nonstoichiometry in Alq3 metal complex. The research was financially supported by the Russian Science Foundation grant N 14-13- 01074.
References: [1] M. Brinkmann et al. J. Am. Chem. Soc., 122 (21) (2000) 5147–5157 [2] R. I. Avetisov et al. Russian Microelectronics, 43(8) (2014) 526–530
S09-P13 Two-dimensional thermoluminescence method for checking crystals homogenity
B. Marczewska, P. Bilski, W. Gieszczyk, M. Kłosowski
Institute of Nuclear Physics PAN, ul. Radzikowskiego 152, 31-342 Kraków, Poland e-mail:[email protected]
The inhomogeneous location of the impurity atoms or intentionally added activators occurs naturally during a crystal growth. Thermoluminescence (TL), being one of the common luminescence methods, is very sensitive to the presence of any impurity. In principle, in TL materials the trapping centres, connected with dopants in the bulk matrix, act as memory cells for radiation deposition events. Subsequent supply of thermal energy to the matrix leads to a release of charge carriers trapped in these centers and their recombination with emission of light (TL). The TL properties of the material are thus connected with the trap distribution in the bulk matrix structure and trap activation, by the presence of dopants and/or by lattice defects. If in a TL reader a CCD camera was used, a measurement of TL signal would give us an unique two-dimensional (2-D) picture of TL signal distribution, and thereby the distribution of dopants. The aim of the work is to study the possibility of the application of 2-D TL method for the control of uniformity of the crystal related to dopant distribution in the volume of the bulk crystal. The 2-D TL method will be presented on LiF crystals doped with Ti and Mg which were grown at IFJ PAN in Kraków by Micro-Pulling Down (MPD) method in the form of thin rods and bulk crystals obtained by Czochralski technique. The crystal rods of the diameter of about 2mm were cut into small pieces, bulk crystals (with a diameter up to 20mm) were longitudinally and transversely cut into slices of the thickness of 1mm. The surface of the slices were softly polished and rinsed. Then the samples were irradiated in an uniform radiation Co-60 field to activate the color centers connected with the dopants. Next the samples were read out in a 2-D TL reader constructed at IFJ PAN. TL reader is equipped with a 60 mm diameter steel planchet heater, the temperature of which can be raised linearly up to the temperature of 400°C with heating rates ranging with time over the range from 1°Cs−1 to 10°Cs−1. The recording of the signal is realized by PCO SensiCamTM VGA CCD 12-bit camera with registering of light signal with dynamic range up to 4500 counts per pixel. The investigation revealed the lack of uniformity in the TL properties on the large surface of LiF crystals up to a few cm2 which is connected with the non-uniform distribution of Ti and Mg atoms. Although 2-D TL method cannot substitute more precise quantitative methods, it can however be applied as an excellent tool for checking the homogeneity of crystals.
Acknowledgments: This work was supported by the National Science Centre (Contract No. DEC- 2012/05/B/ST5/00720).
S09-P14 Disorder control of nanostructural arrangement in AlGaN/GaN light-emitting structures and related phenomena
A.E. Chernyakov1, M.E. Levinshtein2, М.М. Kulagina2, V.N. Petrov2, I.N. Smirnova2, S.I. Troshkov2 ,N.A. Talnishnikh1, E.I. Shabunina*2, N.M. Shmidt2 , A.P. Kartashova2 , A.S. Usikov3, S.Yu. Kurin3 , H. Helava3 , Yu. Makarov3
1Science and Technology Center of Microelectronics and Submicrometer Heterostructures, RAS, Polytekhnicheskaya 26, 194021, St. Petersburg, Russia 2Ioffe Physical Technical Institute, Polytekhnicheskaya 26, 194021, St. Petersburg, Russia, [email protected] 3Nitride Crystals, Inc. 181E Industry Ct., Ste. B, Deer Park, 11729, NY, USA. *email: [email protected]
The disorder of nanostructural arrangement (NA) in layers and light-emitting structures (LES) based on III-nitrides is evoked by growth conditions, the lattice constants mismatch and tetrahedral radiuses. Numerous forms of NA appear as different surface morphology of the structures grown. As a result, the surface monitoring by means of atomic force microscopy (AFM) allows us to determine NA disordering quantitatively by the AFM data processing using methods of multifractal analysis [1,2]. The effectiveness of this approach to study the properties of GaN layers and high- power blue InGaN/GaN LEDs was shown earlier [1,2]. It is assumed to be an effective tool to find out the reasons behind the low external quantum efficiency (~ 2%) and short lifetime (~ 2000 h) in AlGaN/GaN LEDs. The quantitative evaluation of nanomaterial disorder in UV AlGaN/GaN LES has not been assessed yet and its connection to the LED’s parameters has not been studied previously. In this work we present the first results of NA disordering characterization of multilayer AlGaN/GaN light-emitting structures (360-365 nm) grown by hydride vapor phase epitaxy (HVPE) on sapphire substrates. A variation of the buffer layer growth conditions allows one to grow 3 types of structures with a different degree of disorder (p): 0.348, 0.370, and 0.390. The p values were determined by the same way as [1,2]. The external quantum efficiency (η) was varied from 1.5% to 0.6% accordingly. The p values are higher than that in InGaN/GaN light-emitting structures (р< 0.345) having η higher than 40% but similar to those having low η values (less than 5%). It was found out that for AlGaN/GaN LEDs an increase in р is accompanied by: 1) a rise in the direct and reverse current at the low voltage (U < 3 V) and the conductivity of the leakage paths (shunts) localized at extended defects such as V-defects [3] and stacking faults piercing p-n junction; 2) a growth in the level of low-frequency noise spectral density (SI); 3) the appearance of local areas with compositional instabilities in AlGaN reducing a local barrier height in LEDs; 4) increasing crowding effect which might be revealed from the voltage fluctuations’ dependences SV on current. These phenomena in AlGaN/GaN LEDs are more prominent than those in high quality InGaN/GaN LEDs, but very similar to those in InGaN/GaN LEDs with high NA disordering (p > 0.350) and low η values (less than 5%). The discussed effects may contribute into such phenomena as the external quantum efficiency droop and reduced lifetime in AlGaN/GaN LEDs.
Acknowledgements The work was supported by Russian Foundation for Basic Research (grants 14-02-31358 and 14- 02-00087) and Presidium of Russian Scientific Foundation (grant 9А32RAN)
References [1] Shmidt N.M. et al., Nanotechnology, 12 (2001), 471. [2] Chernyakov A.E. et al., Microelectronics Reliability, 52 (2012), 2180. [3] Moseley Michael W. et al., Journal of Applied Physics, 117 (2015), 095301.
S09-P15 Effect of gamma irradiation on the optical properties of CVT grown ZnSe single crystals P. Kannappan1,2, K. Asokan3, K. Baskar1, J. P. Leitao2, R. Dhanasekaran1* 1Crystal Growth Centre, Anna University, Chennai-600 025, India 2Department of Physics and I3N, University of Aveiro, 3810-193 Aveiro, Portugal 3Inter University Accelerator Centre, New Delhi-110 067, India *email: referring author email: [email protected]
ZnSe is an important material for detectors in the high energy radiation environments. This semiconductor exhibit high radiation stability with high upper limit of working temperature. Hence it is a very promising material for ‘scintillator photodiode’ detectors. In this work we present, the effect of gamma irradiation on the optical properties of ZnSe. The ZnSe crystals were grown by chemical vapour transport (CVT) method with iodine as a transporting agent using two zone horizontal resistive heating furnace. During the growth, the temperature difference between the two zones was maintained at 50˚C with the source temperature of 900˚C and the growth temperature of 850˚C. The growth period was about 15 days. The largest dimensions of 9×7×5 mm3 crystals were obtained. Concerning the structural investigation, XRD analysis showed a cubic zinc-blend crystalline phase. The composition of grown ZnSe crystal has been determined by EDXRF analysis as Zn (52.5%) and Se (47.5%). The gamma-irradiation was performed using 60Co source with doses in the range of 10 to 250 kGy at room temperature. The electronic energy levels structure of gamma irradiated samples was studied by room temperature photoluminescence (PL) measurements. The band edge emission at 439 nm (2.82 eV) is the dominant peak. In addition, the defect related peaks were observed in the low energy side of the PL for both pristine and irradiated samples. The PL peak shows a blue shift and increases in intensity with increase of gamma dose. The FT-Raman study was performed in order to understand the lattice vibrations of gamma irradiated samples. All these results will be discussed based on the dependence of gamma dose.
S09-P16 Thermal stability of ferroelectric domain gratings in Rb-doped KTP
Gustav Lingren1, Alexandra Peña*2,3, Andrius Zukauskas1, Charlotte Liljestrand1, Bertrand Ménaert2,3, Benoît Boulanger2,3, Carlota Canalias1
1Departement of Applied Phyisics, Royal Institute of Technology, Roslagstullsbacken 21, 10691 Stockholm (Sweden) 2Univ. Grenoble Alpes, Inst NEEL, F-38042 Grenoble (France) 3CNRS, Inst NEEL, F-38042 (France) *email: [email protected]
Rb-doped KTiOPO4 (RKTP) has proven to be one of the best materials for nonlinear optical frequency conversion using quasi-phase matching (QPM). QPM is most commonly implemented by periodically inverting the spontaneous polarization in ferroelectric crystals. The most-well developed and reliable domain-engineering technique relies on electric field poling with finger electrodes deposited by lithographic techniques [1]. However, state-of-the-art nonlinear optical applications demand high aspect-ratio ferroelectric domain gratings, ranging from sub-µm periodicities to large aperture crystals. Indeed, RKTP has demonstrated to be a promising candidate for these types of applications [2, 3]. Nevertheless, variations in the coercive field due to inhomogeneous stoichiometry over a single crystal wafer results in poor electric-field poling yield, especially for thick crystals with short grating periods. Recently, an alternative technique [4] for obtaining QPM devices has been successfully demonstrated for KTiOPO4. In this method, a periodically poled (PP) crystal is used as a template for epitaxial growth of high quality crystals, preserving the original domain structure of the seed, opening up the possibility to grow large-aperture crystals with short periodicity. Thus, RKTP is an excellent candidate for template growth: Not only does its orders of magnitude lower ionic conductivity facilitate the template fabrication; it also shows superior resistance to optical damage due to lower light-induced absorption in the blue-green spectral region [5], which, of course, will be most beneficial for practical applications. Nevertheless, although the epitaxial growth of periodically poled crystals is performed below the Curie temperature, the thermal stability of the domain gratings at elevated temperatures becomes an issue of utmost importance. In this work we study the stability of DWs in periodically poled RKTP at high temperatures. We demonstrate that annealing the crystals above 550 °C induces DW motion. This motion is highly anisotropic along the a- and b- crystallographic axes. Along the b-axis we observe tens of micrometers domain contraction, whereas in a-direction the result is either orders of magnitude lower DW motion or domain merging, depending on the initial domain configuration. Moreover, we show that the DW stability depends on the period of the QPM device, leading to complete back switching for sub-µm periods.
References: [1] Yamada M., Nada N., Saitoh M., Watanabe K., Appl. Phys. Lett., 62 (1993) 435. [2] Zukauskas A., Thilmann N., Pasiskevicius V., Laurell F., Canalias C., Opt. Mater. Express, 1 (2011) 201. [3] Zukauskas A., Strömqvist G., Pasiskevicius V., Laurell F., Fokine M., Canalias C., Opt. Mater. Express, 1 (2011) 1319. [4] Peña A., Ménaert B., Boulanger B., Laurell F., Canalias C., Pasiskevicius V., Segonds P., Félix C., Debray J., Pairis S., Opt. Mater. Express, 1 (2011) 185. [5] Zukauskas A., Pasiskevicius V., Canalias C., Opt. Express, 21 (2013) 1395.
S09-P17 Argon ion irradiation effects on CdZnTe crystals: influence of the substrate temperature
J.L. Plaza1, O. Martínez2, E. Repiso1, S. Rubio1 and E. Diéguez1
1Laboratorio de Crecimiento de Cristales, Departamento de Física de Materiales, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049, Madrid (España) 2 GdS-Optronlab Group, Departamento Física Materia Condensada, Universidad de Valladolid, Edificio I+D, Paseo de Belén 11, 47011 Valladolid, Spain *email: [email protected]
CdZnTe (CZT) crystals find interesting uses in a variety of detector-type applications. This is due to its large absorption coefficient, high resistivity, high average atomic number and large band gap [1]. The performance of CZT is affected by point defects, as well as structural and compositional heterogeneities within the crystals, such as grain boundaries and Te inclusions. These last kind of defects are created during the growth process and the cooling down phases [2] as a result of the retrograde solid solubility of Te and a poor stoichiometric control [3]. The concentration and distribution of Te inclusions within a device are one of the major contributions to the degradation of CZT detectors. Te precipitates on the surface can also increase the leakage current [4,5], thereby deteriorating the device performance. Te inclusions and precipitates also act as traps for the charge carriers, affecting to the charge collection efficiency as well as the energy resolution of the detector. Our previous studies clearly revealed a pronounced effect when CZT surfaces were irradiated with Ar ions at room temperature. Even for small fluences, a removal of polishing scratches on the sample surfaces was observed. Correlated to this effect, an important enhancement in the luminescence intensity of the irradiated samples was observed. Te inclusions also tend to aggregate after the irradiation process and are also eliminated from the surfaces for the highest ion fluences [6]. In this work the effect of the temperature of the sample in the range 300-600 K during Ion Beam Sputtering of CZT crystals surfaces at different fluences is analised by means of Scanning Electron Microscopy , Atomic Force Microscopy, Raman and Photoluminescence. It is expected that increasing the temperature of CZT samples during the irradiation process will enhance the beneficial effects this technique has shown when trying to reduce surface Te inclussions and to increase the luminescence properties of CZT crystal surfaces.
References: [1] H. Bensalah, J.L. Plaza, J. Crocco, Q. Zheng, V. Carcelen, A. Bensouici, E. Diéguez, Appl. Surf. Sci. 257 (2011) 4633. [2] P. Rudolph, Cryst. Res. Technol. 38 (2003) 542. [3] Robert Triboulet, Paul Siffert, CdTe and Related Compounds; Physics, Defects, Hetero- and Nano-structures, Crystal Growth, Surfaces and Applications (European Materials Research Society Series), Institute of Leadership & Mana, The Netherlands, 2010. [4] T. Wang, W. Jie, D. Zeng, Mater. Sci. Eng. A 472 (2008) 227. [5] H.Y. Pei, J.X. Fang, Phys. Status Solidi A 188 (2001) 1161. [6] H. Bensalah, V. Hortelano, J.L. Plaza, O. Martínez , J. Crocco, Q. Zheng, V. Carcelen, E. Dieguez, J. Alloys and Compounds 543 (2012) 233.
S09-P18 On Defects Detection in Crystals using Image Processing and Pattern Recognition Tools
Moshe Porat
Computer Vision Laboratory Department of Electrical Engineering Technion Haifa 32000 Israel [email protected] and [email protected]
Most crystals contain small inclusions and imperfections. These defects interfere with the passage of waves through the crystal and affect its reflections (e.g., X-Ray [1], visible light [2]) thereby help assessing its quality and the potential use of the crystal. Based on recent developments in image processing and computer vision, in this work we introduce new tools for crystal inspection. Understanding the defect type and other key features of a crystal can also be achieved by applying pattern recognition technology. We have tested tools of shape analysis, pattern matching, spectral analysis, image retrieval and image registration. Localized descriptors have been used in this work to represent the crystal normalized to cope with potential geometric transformations of the crystal due to various viewpoints [3]. De-noising statistical tools have been applied to remove noise [4], and image registration have been used to associate the same defects of the crystal from different directions. The proposed tools and their performance are presented along with practical results based on actual crystals. Our conclusion is that the proposed approach to crystal inspection using machine-vision tools could be helpful in the task of crystals quality control and could improve presently available inspection methods.
Figure 1. Defects detected using the proposed tools for the same crystal illuminated from various directions.
References: [1] B. Raghothamachar, G. Dhanaraj, J. Bai and M. Dudley, "Defect Analysis in Crystals using
X‐ray Topography", Microscopy Research and Technique, Vol. 69 (2006), pp. 343-358.
[2] M. Porat, "An Image Processing Approach to Diamond Inspection and Evaluation", 24th European Crystallographic Meeting (2007) Acta Cryst. A63 (2007) pp. s79. [3] M. Porat and G. Shachor, "Signal Representation in the Combined Phase-spatial Space: Reconstruction and Criteria for Uniqueness", IEEE Trans. on Signal Processing, Vol. 47 (1999), pp. 1701–1707.
[4] S. Nemirovsky and M. Porat, "Method and System for Processing an Image According to Deterministic and Stochastic Fields", US patent 8,537,172 (2013).
S09-P22 Mystical source of electrically active chlorine at Cl doped CdTe
Lukáš Šedivý*,1, Jakub Čížek2, Eduard Belas1 and Roman Grill1
1Institute of Physics, Charles University in Prague, Ke Karlovu 5, CZ-121 16, Prague 2, (Czech Republi) 2Department of Low-Temperature Physics, Charles University in Prague, V Holešovičkách 2, CZ-180 00, Prague 8, (Czech Republic)
CdTe/CdZnTe is an excellent material for manufacture of x-ray and gamma-ray room-temperature detectors thanks to large linear attenuation coefficient, the possibility to make it high-resistive CdTe/CdZnTe at room temperature, and satisfactory electron mobility and life-time. An engineering of point defects existing in CdTe/CdZnTe crystals represent dominant task for routine productions of detectors. Annealing in well defined ambient component pressure, Cd or Te, is a standard procedure to directly influence the density of native point defect, like cation and anion vacancies, cadmiun and telurium interstitials, and their complexes with extrinsic impurities. Defects form energy levels in band gap and affect resistivity and carrier life-time. Detailed understanding of the effect of annealing to the point defect structure is crucial to get the optimal preparation method of CdTe/CdZnTe radiation detectors. Divalent acceptor Cd vacancy and its complexes with extrinsic substituting donors seated both in cation and in anion sublattice are considered the most important for the defect self-compensation and for preparation of high resistive material. In spite of the enormous effort in the past decades to fix properties of Cd vacancies in CdTe/CdZnTe, namely formation and ionization energies and large scatter of these quantities is found in the literature. The high-temperature in situ galvanomagnetic measurements in classical Hall-bar six probe configuration (HT-Hall) are used for observation of equilibrium concentration of native and extrinsic point defects at high temperature. Positron annihilation spectroscopy (PAS) are used for studiing of acceptor-type defects. Positron trapping at defects change their annihilation characteristics and allows us to deduce the density of the defects. Simultaneously, when PAS is done at various temperature, an information of charge state of the defect may be estimated. In this work we report on HT-Hall measurement in CdTe doped by chlorine or indium. The relaxation of electrical conductivity and free carier concentration after step-like change of surrounding Cd pressure was measured at high temperature and the chemical diffusion coefficient was evaluated. The equilibrium concentration of native and extrinsic point defects was evaluated from Hall effect measurement using theoretical model [1]. In parallel, PAS in as grown, Cd-annealed and Te-annealed Cl-doped CdTe , was done for native and extrinsic point defects identification.
References: [1] Grill R., Franc J., Höschl P., Turkevych I., Belas E., and Moravec P., IEEE Trans. Nucl. Sci. 52 (2005) 1925.
S09-P23 Structural examination of multilayer CrAlN/AlSiN films
Dimitrios Chaliampalias1,George Vourlias1, Eleni Pavlidou1, Nikolaos Vouroutzis1, Lilyana Kolaklieva2, Roumen Kakanakov2, Vassiliy Chitanov2, Tetyana Cholakova2, Efstathios K. Polychroniadis*1
1Aristotle University of Thessaloniki, Physics Department, University Campus, 54124, Thessaloniki (Greece) 2 Central Laboratory of Applied Physics, BAS, 61 St. Petersburg Blvd., 4000 Plovdiv (Bulgaria) *email: [email protected]
The deposition of transition metal nitrides on metallic components is a widely applied technology for the modification of the surface properties of the materials. At the first stages the deposition of binary nitrides was investigated, such as TiN, CrN and ZrN. This technology has evolved by the deposition of ternary and quaternary nitrides. Latter progress on such films focuses on the deposition of multilayer nitrides which were found to improve significantly the mechanical properties and oxidation resistance. This happens because of the existence of many interfaces in the film which have a double effect; they restrict the dislocation propagation because of the crack dissipation when reaching those areas while the thermal stability is also improved as the increased interfaces act negatively to the diffusion of ion species. In the herein work the structure of multilayer CrAlN/AlSiN deposited by Cathodic Arc Deposition is examined. The deposition was performed using a Platit π80+ unit by a cathodic arc process equipped with a Lateral Arc Rotating Cathode (LARC) system. Firstly a bonding layer was deposited which contained non-stoichiometric to stoichiometric CrNx compound followed by a gradient nanocomposite Cr/Al/Si/N layer formed by manipulating the cathode current. After these bonding layers nanocomposite AlSiN/SiN and CrAlN/SiN layers were successively deposited. The latter process was repeated three times in order to create three repeating periods. The as formed films were examined by Electron microscopy (SEM, TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that the as deposited coatings are composed of seven distinct layers with a total thickness 9μm (Fig.1a). Though the stress created on the interfaces, no cracks or deformations were observed in any area of the film. EDS analysis on several regions of the film revealed that the light colored layers contain Cr while the dark ones not. The layer in contact with the substrate is the bonding layer and contains higher Cr amounts. These observations are verified in the corresponding line scanning image (fig. 1b) in which the variation of Cr is clearly illustrated. Moreover it is revealed that in the Cr rich layers the Al concentration decreases. From XRD and XPS examination it was found that on the surface the (Cr,Al)N solid solution is the predominant phase. XPS tracked some minor oxides of Al and Cr which result from the high affinity of Al and Cr to low oxygen amounts existing in the deposition chamber.
Fe Cr 10μm Si Al Cr Al B ri ri on ch ch di la la ng substrate ye ye la r r ye r
Figure 1. Cross sectional SEM micrograph (a) and corresponding line scanning of the as deposited films.
Acknowledgement: This work was supported from ΙKY Fellowships of excellence for postgraduate studies in Greece – Siemens Program
S09-P26 Dislocation mechanism of KDP growth from solution
H.V.Alexandru*1
1Universuty of Bucharest, Faculty of Physics, Bucarest (Romania) *email: [email protected]
Macroscopic growth kinetic measurements of pyramidal faces of KDP crystal were performed in dynamic regime. Three crystals were simultaneously grown in the same conditions, by temperature decreasing method. Arrhenius corrections were made to 40°C growth temperature, for our data and for some literature data; we have used to compare with. Surface diffusion mechanism of growth appears as essential at small supersaturations, but several particular aspects dominate the growth. Pyramidal faces are less sensitive to impurities and show a large dispersion of the growth kinetic at σ ≈ 0.01-0.05. There are distinct BCF curves fitting the experimental data on several ranges of supersaturations, corresponding to several efficiencies of growth. Bürgers vector and the linear dimension of the dominant centers of dislocations involved during growth are discussed.
SESSION 10
Nanostructures & Nanoporous Crystals
Nucleation approach to polytypism in III-V nanowires
Jonas Johansson*1, Zeila Zanolli2,3, Kimberly A. Dick1,4
1Solid State Physics, Lund University, Box 118, 22100, Lund (Sweden) 2Peter Grünberg Institute & Institute for Advanced Simulation, Forschungszentrum Jülich, 52425 Jülich (Germany) 3 European Theoretical Spectroscopy Facility (ETSF) 4Center for Analysis and Synthesis, Lund University, 22100, Lund (Sweden) *email: [email protected]
Several III-V nanowire materials systems exhibit features of polytypism, which is a kind of polymorphism, where the polymorphs differ only in the layer stacking sequence. In bulk, all III-V semiconductors, except nitrides, exhibit the zinc blende structure (3C polytype). However, when these materials are grown as nanowires, they often exhibit a seemingly random crystal structure and by tuning the growth parameters, more or less pure 3C or 2H can be fabricated. Sometimes often higher order polytypes, such as 4H and 6H form. In order to use III-V nanowires in electronic and optoelectronic applications, it is of highest importance to control and possibly also take advantage of the polytypism. In our current investigations, we take a classical nucleation approach to explain the phenomenon of polytypism in metal particle-seeded III-V nanowires, including polytypes up to 6H. In order to describe the formation of higher order polytypes, interaction between the stacked layers, which goes beyond nearest neighbor interactions must be taken into account. For this purpose we use the axial next nearest neighbor Ising (ANNNI) model [1]. In this model, the stacking sequence is treated as a sequence of generalized spins and different sequences give different total energies, depending on the interlayer interaction parameters. We will show how the total energies for several polytypes can be calculated using ab initio techniques for any given material. In addition, from the total energy expressions a phase diagram can be constructed, in which the ab initio results can be visualized. Using this approach, it has been shown that 6H is the most stable SiC polytype and it has been verified that the III-V semiconductors are very stable in 3C. Another, more kinetic approach to the ANNNI modeling of polytypism is to keep track of the incremental energy change due to the addition of single layers. This approach has been used to explain the preference of SiC to grow in the 3C polytype during CVD. In our approach to polytypism in nanowires, we use the ANNNI model to express the interface energy between the forming nucleus and the underlying layers for the 3C, 6H, 4H, and 2H polytypes. We will show how to combine this interface energy with our nucleation theoretical framework and describe how we can use this model to calculate the formation probabilities of these four polytypes as functions of supersaturation. Depending on the interaction parameters, the range of attainable polytypes as a function of supersaturation can vary, and this can be graphically represented. For this purpose we will introduce polytype attainability diagrams and discuss their experimental relevance.
References: [1] Selke W., Physics Reports, 170 (1988) 213. [2] Johansson J., Bolinsson J., Ek M., Caroff P., Dick K. A., ACS Nano, 6 (2012) 6142.
InAs/GaAs SHARPLY-DEFINED AXIAL HETEROSTRUCTURES IN SELF-ASSISTED NANOWIRES D. Scarpellini1,2, C. Somaschini1, A. Fedorov3, S. Bietti1,*, C. Frigeri4,V. Grillo4,5, L. Esposito1, M. Salvalaglio1, A. Marzegalli1, F. Montalenti1, E. Bonera1, P. G. Medaglia2 and S. Sanguinetti1 1L–NESS and Dipartimento di Scienza dei Materiali, Università di Milano Bicocca, Milano, Italy, 2Department of Industrial Engineering University of Rome Tor Vergata, Rome, Italy, 3LNESS and CNR-IFN, Como, Italy, 4CNR-IMEM Institute, Parma, Italy 5CNR-S3-NANO Center, Modena, Italy *email: [email protected]
Semiconductor nanowires (NWs) are one of the most promising technologies for the development of quantum devices such as single quantum dot emitters, single-electron transistors and tunnel FET. Due to the reduced size of the interfaces, NWs can be used for the growth of highly mismatched materials. However, the growth of the technologically relevant InAs/GaAs interface in axial heterostructures with atomically sharp interfaces have never been achieved in MBE self-assisted growth, thus hindering the use of this materials for the fabrication of several devices. In this presentation we show the procedure for the fabrication of axial, self-assisted, InAs/GaAs NW heterostructures on silicon with atomically sharp interface, by decoupling the growth of GaAs NW and InAs segment [1]. The lower GaAs segment is realized by growing self-assisted GaAs NWs on Si (111) substrates, while the upper InAs segment is fabricated in a two-step process by supplying In and As separately, resembling the droplet epitaxy procedure for the fabrication of quantum dots [2]. Scanning transmission electron microscopy with High Angle Annular Dark Field detector (HAADF, figure 1a) confirms the formation of InAs on the top of the GaAs NWs. High resolution TEM (HR-TEM, point resolution 0.18 nm, figure 1b) demonstrates the formation of an atomically sharp interface. The lattice parameters calculated by using the position of the <111> spot in power spectra of HR-TEM (insets of figure 2b) are in agreement with the ones of InAs and GaAs.
Figure 1. Panel (a): High resolution STEM-HAADF image of the InAs/GaAs NW tip. Panel (b): HR–TEM of the layer of GaAs and the top InAs. The power spectra of InAs and zincblend GaAs are shown as insets
References: [1] D. Scarpellini, C.Somaschini, A.Fedorov, S.Bietti,C.Frigeri, V.Grillo, L.Esposito, M.Salvalaglio, A.Marzegalli, F.Montalenti, E.Bonera, P.G.Medaglia and S.Sanguinetti, Nano Letters (published online) DOI: 10.1021/nl504690r [2] N. Koguchi, K. Ishige, and S. Takahashi, J. Vac. Sci. & Technol. B 11, 787 (1993).
Mass-transport driven growth dynamics of AlGaAs shells deposited by metalorganic vapor phase epitaxy around dense GaAs nanowire ensembles
Ilio Miccoli1, Paola Prete2, Nico Lovergine*1
1Dip. di Ingegneria dell’Innovazione, Università del Salento, I-73100 Lecce, Italy 2Istituto per la Microelettronica e Microsistemi, CNR, UOS Lecce, I-73100 Lecce, Italy *email: [email protected]
III-V compounds nanowires are expected to impact several device technology fields, ranging from nanoelectronics, to nanophotonics, and photovoltaics, by offering both unprecedented materials properties and novel device geometries/functionalities. Radial modulation of nanowire composition and/or doping in the form of core-shell and core-multishell nanowire heterostructures has been proposed for novel nano-LEDs/-lasers [1,2]. In order to exploit MOVPE technology for the fabrication of such devices, good control over the growth process of radially-heterostructured nanowires is necessary. While many efforts have been devoted in understanding/modelling the Au- catalysed (VLS) growth of III-V nanowires, much less is known on the growth dynamics of shell materials by the conventional (Vapor-Solid) MOVPE around free-standing core nanowires. We report on a detailed experimental analysis of AlGaAs shell growth by MOVPE around free- standing GaAs nanowires, the latter self-assembled by the Au-catalyzed process on (111)B-GaAs wafers or GaAs/(111)Si hetero-substrates [3]. We demonstrate that the vapour mass-transport supply of III-group species during shell growth couples with the nanowire size (e.g. their diameter) and their local surface density on the substrate to determine the actual shell growth rate. A vapor mass-transport model is proposed and validated, describing the MOVPE growth dynamics of the shell material around dense ensembles of GaAs nanowires [4]. We predict a complex (non-linear) dependence of the shell growth rate on initial GaAs nanowire diameters, heights, local densities on the substrate, and deposition time (see Figure 1). Present results constitute a significant step towards the controlled fabrication of core-shell and core-multishell nanowire heterostructures by MOVPE.
(a) (b)
Figure 1: Average diameter of GaAs-AlGaAs core-shell nanowires as function of (a) their substrate surface density (NW) after 10 min shell growth, and (b) the shell growth time for different NW.
References: [1] B. Mayer, D. Rudolph, J. Schnell, S. Morkotter, J. Winnerl, J. Treu, K. Muller, G. Bracher, G. Abstreiter, G. Koblmuller, Nat. Comm. 4 (2013) 2931. [2] K. Tomioka, J. Motohisa, S. Hara, K. Hiruma, T. Fukui, Nano Lett. 10 (2010) 1639. [3] I. Miccoli, P. Prete, F. Marzo, D. Cannoletta, N. Lovergine, Cryst. Res. Technol. 46 (2011) 795. [4] I. Miccoli, P. Prete, N. Lovergine, submitted (2015).
Low Temperayure Growth of Porous ZnO Films for Inorganic–Organic Hybrid Solar Cells
Kenji Yoshino1, 2, *, Akiko Mochihara1, 2, Kenji Kainou1, Minobu Kawano3, Yuhei Ogomi2, 3, Qing Shen2, 4, Taro Toyoda2, 4, Shuzi Hayase2, 3
1Department of Electrical and Electronic Engineering, University of Miyazaki, 1-1 Gakuen Kibanadai-nishi, Miyazaki 889-2192, Japan 2CREST, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan. 3Department of Engineering Science, Faculty of Informatics and Engineering, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan. 4Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, 2-4 Hibikino, Wakamatsu, Kitakyushu 808-0196, Japan *email: [email protected]
ZnO exhibits a wurtzite hexagonal structure and its direct optical bandgap of 3.4 eV at RT is wide enough to transmit most of the useful solar radiation. In our previous work [1], non-doped ZnO films were successfully grown on a polyethylene terephthalate film by a conventional spray pyrolysis at 150 ˚C using a diethylzinc (DEZ)-based solution under an air atmosphere. It is well known that the DEZ reacts with water and/or oxygen at low temperature, and ZnO can be generated. In this work, novel precursor solutions were prepared by the reaction of DEZ and water in some solvent. Diethoxyethane and/or other ether solvents were used for the solution. In sample preparation, all operations were carried out under inert gas (e.g. nitrogen). The hydrolysis reaction was carried out by addition of water to DEZ in solvent under cooling condition to remove reaction heat and avoid side reactions. After aging the reaction mixture at RT for 2 hours, the novel precursor solution containing Zn-O structure compound was obtained. A novel precursor for ZnO film deposition with Zn-O structure was synthesized by the reaction of DEZ and water in some ether solvents. Non-doped ZnO films on a glass substrate have been successfully grown by conventional spin coating using the novel precursor solution. Strong and clear X-ray diffraction peaks of ZnO film grown by the novel precursor solution are observed compared to those grown by simple DEZ solution. The samples have an optical transmittance of more than 85%, and a porous surface determined from optical transmittance and scanning electron microscopy (Fig.1), respectively. We also apply for perovskite based solar cell instead of TiO2.
o T =150 C S
500nm 500nm 500nm Fig.1 SEM images of the surfaces of non-doped ZnO/glass films using different solvent grown by spin coating at 150 °C .
References: [1] K. Yoshino, Y. Takemoto, M. Oshima, K. Toyota, K. Inaba, K. Haga, and K. Tokudome, Jpn. J. Appl. Phys. 50 (2011) 040207.
Growth of ZnO nanostructures through rapid crystallization
Fioravanti Ambra*1,2, Bonanno Antonino2, Carotta Maria Cristina2,3, Sacerdoti Michele4
1Dipartimento di Chimica, Università degli Studi di Parma, Parco Area delle Scienze 17A, 43124 Parma (Italy) 2CNR-IMAMOTER, Via Canal Bianco 28, 44124 Ferrara (Italy) 3CFR-Consorzio Futuro in Ricerca, Via Saragat 1/B, 44122 Ferrara (Italy) 4Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Via Saragat 1/C, 44122 Ferrara (Italy) *email: [email protected]
ZnO is a II-VI compound semiconductor whose chemical bond is between covalent and ionic, while the most stable phase is wurtzite-type structure belonging to the hexagonal space group P63mc with the lattice parameters a = 3.2499 and c = 5.2066 Å. The research focused on semiconductor ZnO already several decades ago. In recent years, the renewed interest for ZnO has been aroused by the discovery of its aptitude for being grown in a great diversity of nanostructures and of different functional properties. Indeed, ZnO can be grown by a great deal of methods, such as vapour deposition, wet chemical methods, etc., obtaining the widest family of unique nanostructures among all known materials. Novel applications resulted in optoelectronics, hybrid solar cells, sensors, biomedical field. The different nanostructures exhibit a large variety of morphologies such as nanoparticles, nanowires, nanorods, nanosheets, nanoneedles, nanoflowers, etc.. They can be divided in one- (1D), two- (2D) or three-dimensional (3D) structures depending on the number of dimensions in which the material has nanometer modulations [1]. Wet chemical methods have been demonstrated to be a powerful and versatile technique for growing ZnO nanostructures [2]. In this work, precipitation in alkaline water solution of zinc nitrate hexahydrate, using NH3·H2O or HMTA (hexamethylenetetramine) as weak bases, was adopted for all synthesized materials. Moreover the thermal treatments to obtain the crystallization were maintained under 100 °C. XRD analysis showed that all powders exhibited hexagonal wurtzite-type structure. Among the obtained morphologies, here we describe four of them: two constituted by elongated crystals (2D structures), forming flower-like nanostructures (Fig. 1a) or nanoneedles (Fig. 1b). In the first case the elongated nanocrystals (in the [0001] direction) are hexagonal prisms that are connected at a central point, where a probable twinning from the (000 ) plane occurred. In the second one, the elongated crystals ended on an hexagonal base pyramid. The second two morphologies (3D structures) can be described as nanoparticles, agglomerated in different shapes: bi-pyramidal (Fig. 1c) or nanoflowers (Fig. 1d). For the last material, X Ray diffraction analysis suggests a probable formation of crystallites oriented as the (0001) basal plane.
Figure 1 a,b,c,d. SEM images of flower-like nanostructures, nanoneedles, bi-pyramids and nanoflowers).
References: [1] C. Suryanarayana, C.C. Koch, Hyperfine Interact. 130 (2000) 5–44. [2] Sheng Xu, Zhong Lin Wang, Nanoresearch 11( 2011) 1013-1098.
Heat of Fusion of Nano Crystals
Clain Alexander E., Novins Caleb A. and Amanuel Samuel*
Department of Physics and Astronomy, Union College, 807 Union Street, Schenectady, NY 12308 (USA)
*email: [email protected]
In order to control the size of 2-decanol nano crystals, we physically confined 2-decanol in nano porous silica. Heat of fusion and melting temperatures of the physically confined systems were studies using a power compensated Differential Scanning Calorimeter, DSC. Our results revealed that the melting temperature decreased as the physical size of the materials decreased and a linear relationship is observed between the melting temperature and the inverse of size. This is in agreement with previous experimental observations and qualitative prediction from the Gibbs- Thompson equation.[1-5] The equation, however, assumes that the heat of fusion to be independent of physical size. Our results, on the other had, revealed reduction in the apparent heat of fusion as the physical size decreases. This seeming contradiction can be explained if there were interfacial layer/s of molecules that would not go under phase transition and do not contribute to the energy of transition (heat). The correct heat of fusion should be determined from normalizing the apparent heat by the mass of the material that actually undergoes phase transition and not the total mass. It is difficult, however, to determine the mass of the materials that actually undergoes phase transition from experimental measurements or directly. In a complementary approach, we have previously used a simple geometrical model to estimate the thickness of the non-freezing interfacial layers and estimated the density of the non-freezing layers.[6,7] In this paper, we present our studies how we were able to incorporate the interfacial molecules in the crystallization of secondary alcohols and how this has influenced the apparent heat of fusion.
References: [1] Alba-Simionesco C., Coasne B., Dosseh G., Dudziak G., Gubbins K. E., Radhakrishnan R., Sliwinska Bartkowiak M., J. Phys. Condens. Matter, 18 (2006) R15–R68. [2] Alcoutlabi M., McKenna G. B., J. Phys. Condens. Matter, 17 (2005) R461–R524. [3] Christenson H., J. Phys. Condens. Matter, 13 (2001) R95–R133. [4] Hamilton B. D., Ha J., Hillmyer M. A., Ward, M. D., Acc. Chem. Res. 45 (2012) 414. [5] Huber P., J. Phys. Condens. Matter 27 (2015) 103102. [6] Amanuel S., Bauer H., Bonventre P., Lasher D., J. Phys. Chem. C 113 (2009) 18983–18986. [7] Bauer H. C., Safiq A. D., Dulmaa J., Khraisat A. S., Amanuel S., MRS Proc. 1423 (2012) mrsf11– mrsf1423 – rr06–04.
Filamentary growth of metals
Gunther Richter Max Planck Institute for Intelligent Systems, Stuttgart, Germany
One dimensional nanostructures have the prospect to change the properties of materials used in contemporary devices. Physical properties change with dimension and size. Ceramics, semiconductor and carbon materials are easily synthesized as one dimensional structures with typical diameters of several nanometers and length‐diameter ratios of 1000:1. However, only the metals as one of the oldest are difficult to fabricate in similar geometries. In contrast, micrometer diameter, millimeter length macroscopic metallic nanowires were grown and reported decades ago via the reduction of metal halides, based on a process described already in 1574.
Recently we developed a process to grow perfect defect and flaw free nanostructures with diameters of several ten nanometers, attached on substrates. The initiator mediated filamentary crystal growth process is based on the physical vapour deposition technique. Metals with face centred (Cu, Ag, Au, Pd) crystal structure were synthesized successfully with the new technique. Typical diameters of the nanowhiskers are 100 nm and lengths of up to 200 µm are observed, giving aspect ratios of up to 2000:1.
Microstructure characterization of the nanowires was carried out predominantly by electron microscopy, revealing a perfect, flaw and defect free bulk and surface crystal structure. No dislocations, stacking faults, or grain boundaries were detected. The growth direction is generally along the <110> crystallographic direction of the face centered cubic lattice. The nanowire surface is formed by low indexed crystallographic planes, the {111} and {100}. The overall geometry is dominated by the minimization in terms of surface energy and resembles the Wulff shape. It was not possible to detect impurities from the growth process on the surface or in the bulk of the nanowires. Preliminary tensile and bending test were performed to study the mechanical properties. The nanowires show flow and yield stresses close to the theoretical limits.
Traditional theories attribute the growth of whiskers with the presence of a screw‐dislocation. However, extensive microstructure studies by transmission electronmicroscopy (TEM) in NWs did not reveal any indication that screw dislocations are present in metal NWs. But our work revealed that NWs grow only on substrates where small areas with high surface energies are surrounded by areas with low surface energies. Diffusion of adatoms toward the small high energy areas leads to nucleation and eventually to NW growth.
Fig. 1: Micrographs of Cu NWs: (a) SEM; (b) Dark-field TEM; (c) HRTEM
A comparative numerical analysis of circular and rectangular well nanopatterning on c-plane sapphire substrates for selective area growth of AlN islands
I. Davis Jacob, A. Rosy, G.K.Priya Merline and M.Chitra*
Crystal Growth Centre, Anna University, Chennai (India) *email for correspondence : [email protected], [email protected]
Abstract: A comparative numerical analysis of circular nanopatterning and rectangular nanopatterning has been performed on c-plane sapphire interfaces for selective area growth of AlN islands. This is to reduce the threading dislocations on the GaN epitaxial layers arising due to lattice mismatch between GaN and sapphire. The dislocation density on the GaN epitaxial layers growing on the substrate is expected to decrease when the linear periodicity of the nanopatterning agrees with certain ratios of alternating sapphire and aluminium nitride lattices. Numerical analysis on the one-to-one mapping of the number of unit cells in a given area of c-cut GaN interface with the unit cells on the c-plane substrate comprising of sapphire and aluminium nitride gives rise to two area domains of sapphire which are marked by matched and mismatched boundaries. Sapphire can be patterned or etched periodically in the shape of circular nanowells on the c-plane surface for selective area growth of AlN. The periodicity, patterning density and sizes (diameter) of the aluminium nitride islands were estimated. In addition, the extent of matched sapphire area and the boundary of the mismatched area are calculated. The same parameters are calculated for rectangular nanowells and compared.
Dual-Type Compound Semiconductor Nanowire Arrays
Joona-Pekko Kakko1, Farid Bayramov2,3, Bakhysh Bairamov2, Tuomas Haggrén1, Veer Dhaka1, Teppo Huhtio1, Antti Peltonen4, Hua Jiang5, Esko Kauppinen5, and Harri Lipsanen1
1Aalto University, Department of Micro and Nanosciences, P.O. Box 13500, FIN-00076 Aalto, (Finland) 2 Ioffe Physical-Technical Institute RAS, 194021, 26 Polytekhnicheskaya ul., St. Petersburg, (Russia) 3 St. Petersburg Academic University – Nanotechnology Research and Education Center, Russian Academy of Sciences, St. Petersburg, 194021 (Russia) 4Aalto-Nanofab, Micronova, Aalto University, P.O. Box 13500, FI-00076 Aalto, (Finland) 5Department of Applied Physics and Nanomicroscopy Center, Aalto University, P.O. Box 15100, FI- 00076 Aalto, (Finland) *email: [email protected]
Dual-type nanowire (NW) array is a novel structure, where two types of NWs – with selective-area epitaxy (SAE) and via vapour-liquid-solid (VLS) – are grown side-by-side on a common substrate using metalorganic vapour phase epitaxy (MOVPE). Figure 1 presents the most important steps to fabricate a dual-type array and a false-color SEM image of the structure. In this work, we present the fabrication scheme of the dual-type NW array and present the properties of the novel structure; complex configurations, compositional control, micro-Raman spectroscopy and micro-photoluminescence measurements that reveal the crystalline quality and precautions to avoid the parasitic growth, due to the two subsequent growth steps. Compositional control and complex configurations can be achieved by using different precursor materials or varying growth conditions in the two growth steps. Complex configurations increase light trapping of the structure and compositional contrast introduces an additional band gap, which in turn could widen the absorption spectrum. These qualities are beneficial, for example, in a solar cell application.
Figure 1. Schematic illustration of the fabrication steps for dual-type NW arrays and a SEM image of final GaAs/GaAs dual-type array.
References: [1] Joona-Pekko P. Kakko, Tuomas Haggrén, Veer Dhaka, Teppo Huhtio, Antti Peltonen, Hua Jiang, Esko Kauppinen, and Harri Lipsanen, Nano Letters, 15 (2015) 1679–1683.
chitra: A comparative numerical
POSTER S10-P01 Vapour phase catalyst-free growth of β-Ga2O3 nanowires
Davide Calestani*1, Alabi Aderemi Babatunde2, Nicola Coppedè1, Marco Villani1, Laura Lazzarini1, Filippo Fabbri1, Giancarlo Salviati1, Roberto Fornari3, Andrea Zappettini1
1IMEM-CNR, Parco Area delle Scienze 37/A, Parma (Italy) 2Department of Physics, University of Ilorin, Ilorin (Nigeria) 3Dept. of Physics and Earth Sciences, University of Parma, Parco Area delle Scienze, 7/A, Parma (Italy) *email: [email protected] Gallium oxide can be classified as a transparent conducting oxide (TCO) with the widest transparency range (band gap energy is about 4.9eV), high chemical stability, n-type conductivity, and strong blue photoluminescence (PL). It crystallizes in five known crystalline modifications (α, β, γ, δ and ε phases), among which β-Ga2O3 is the most stable polymorph. The β-phase Ga2O3 is characterized by a monoclinic crystal structure with two distinct gallium sites (six-and four- coordinated) and three oxygen sites (three- and four-coordinated). Native point defects are known to form readily in this complex oxide lattice and are responsible for a range of important physical properties. Specifically, oxygen vacancies have been proposed to lead to the formation of shallow donor states which are considered to be the source of n-type electrical conductivity. In recent years, low-dimensional β-Ga2O3 structures including NWs, nanobelts, nanorods and nanosheets have attracted growing attention of researchers due to their superior properties as compared to their bulk counterpart. One very important advantage of β-Ga2O3 NWs is their large surface to volume ratio providing more surface states to interact with the surroundings. The strong blue light emission property of the Ga2O3 nanobelts also suggests them as new candidates for fabricating functional optoelectronic nanodevices and nanosize sensors. In this work we report the successful synthesis of β-Ga2O3 nanowires/nanobelts using simple a physical evaporation technique, derived from previous experiments on the vapour phase growth of metal oxide nanostructures from a simple metal source. Nanostructures have been grown on different kind of substrates (silicon, alumina, sapphire) starting from metallic Ga source that, in the proper alternation of argon and argon-oxygen mixture atmospheres, evaporates, deposits and finally feeds the growing nanocrystals by reaction with oxygen in the proper temperature range. No catalyst have been used to force the nucleation of nanowires and no metal-organic precursor have been used, so that only high purity β-Ga2O3 nanostructures can be obtained. As a case of study, nanowires have been grown also on Au and Pt films for comparison. The morphological, structural and optical properties of the obtained nanostructures have been characterized, revealing thin (mainly ranging from 5 to 20 nm) and long (up to tens of micrometers) nanowire- or nanobelt-shaped crystals. Their properties have been studied by means of SEM and TEM microscopy as well as cathodoluminescence, mainly comparing results obtained for different growth conditions and substrates.
Figure 1. SEM image of β-Ga2O3 nanowires and nanobelts obtained on alumina substrate
S10-P03 Bioceramic Coatings Produced on Commercially Pure Titanium by the Induction Heat Treatment and Nanostructure Surface Modification
Fomin Aleksandr*1, Fomina Marina1, Rodionov Igor1, Koshuro Vladimir1, Poshivalova Elena1, Zakharevich Andrey2, Skaptsov Aleksandr2, Atkin Vsevolod2
1 Yuri Gagarin State Technical University of Saratov, 410054, Politekhnicheskaya, 77, Saratov, (Russia) 2 Saratov State University named after N.G. Chernyshevsky, 410012, Astrakhanskaya, 83, Saratov, (Russia) *email: [email protected]
In medical practice commercially pure titanium and medical titanium alloys are widely used when joint endoprostheses and dental implants are fabricated. It is especially important to produce biocompatible materials and coatings that improve osseointegration [1]. The implant coatings should have high morphological heterogeneity of the micro- and nanostructure [2]. The surface modification is usually performed by plasma spraying, oxidation, etc. A characteristic feature of these methods is high energy consumption, complex technological sequence, decreased mechanical strength together with high porosity, relatively long duration in order to obtain the required phase- structural state. The surface of the titanium samples was oxidized using induction heat treatment (IHT). As a result of IHT the oxide coatings of titania (TiO2) were formed. The next step included colloidal modification with hydroxyapatite (HAp) nanoparticles. The IHT effect in the temperature range of 600...1200 °C on the performance of structure and properties of the coatings was determined. Titania coating production included the formation of dotted, needle-like, plate, and prismatic crystals (Fig.1a). Oxide coatings were modified with HAp nanoparticles (Fig.1b,c). Increased cellular activity and accelerated osseointegration on the surface of implants with nanocrystalline coatings were observed [2].
Figure 1. Morphology of coatings: a – TiO2 coating; b,c – TiO2 + HAp coating
The research was carried out with financial support of grant RFBR 13-03-00898 “a”, scholarship SP-617.2015.4, and project 1189 in the framework of the basic part of the state educational task for institutions of higher education, under the jurisdiction of the Ministry of Education of the Russian Federation in the field of scientific activity.
References: [1] Dorozhkin S.V., Biomaterials, 31 (2010) 1465-1485. [2] Fomin A.A., Rodionov I.V., Steinhauer A.B., et al., Proc. of SPIE, 9031 (2014) 90310H.
S10-P04 Metal-Oxide Coatings with Ultrafine Crystalline Structure on Medical Implants Fabricated from Stainless Steel
Rodionov Igor*, Fomin Aleksandr, Fomina Marina, Poshivalova Elena, Koshuro Vladimir
1 Yuri Gagarin State Technical University of Saratov, 410054, Politekhnicheskaya, 77, Saratov, (Russia) *email: [email protected]
The structure of metal-oxide coatings produced on stainless steel 12Cr18Ni9Ti by thermal modification in the air was studied using scanning electron microscopy (SEM) [1,2]. The influence of heat treatment of medical implants during osteosynthesis on the changes in the morphological parameters of coatings, their dimensional structural characteristics was determined. In the course of SEM studies it was determined that during thermal modification of the surface of steel substrates in the air polycrystalline metal-oxide films with ultrafine structure were formed (Fig.1a). Under the studied conditions at the temperatures of 350 and 400 °C and oxidation duration of 1.5 hours the production of both bulk and surface structure of coatings was characterized by the formation of numerous nucleations and growth of oxide particles (Fig.1b). The coatings acquired mainly fine structure, the specific feature of which was increased porosity and microheterogeneity. Based on the studies of the characteristics of heterogeneous oxide coatings produced on substrates of medical stainless steel by gas-thermal oxidation it was found that the resulting thin coatings have the ability to ingrow into the bone (Fig.1c). The application of the developed coatings under osseointegration of steel orthopedic implants into different bone segments is explained.
Figure 1. Micro- (a) and nanostructure (b) of an oxide coating and the intraosseous part of an oxidized implant with bone fragments after in vivo testing (c)
The research was carried out with financial support of project 1189 in the framework of the basic part of the state educational task for institutions of higher education under the jurisdiction of the Ministry of Education of the Russian Federation in the field of scientific activity, grant of the President of the Russian Federation MD-3156.2015.8 and grant RFBR 13-03-00248 “a”.
References: [1] Rodionov I.V., Inorganic Materials: Applied Research, 4(2) (2013) 119-126. [2] Rodionov I.V., Metal Science and Heat Treatment, 55 (2014) 599-602.
S10-P07 Low Temperature Growth of Ga-doped ZnO Thin Films Grown by Atmospheric Spray Pyrolysis for CuInGaSe2 Based Solar Cells
Kenji Yoshino1,*, Akiko Mochihara1, Himeka Tominaga1, Youei yamaga1, Takashi Minemoto2, Shigeru Ikeda3
1Department of Electrical and Electronic Engineering, University of Miyazaki, 1-1Gakuen Kibanadai-nishi, Miyazaki 889-2192, Japan. 2Department of 1Department of Electrical and Electronic Engineering, Ritsumeikan University, Kusatsu, Japan 3 Research Center for Solar Energy Chemistry, Osaka University, Osaka, Japan *email: [email protected]
Transparent conductive oxide (TCO) materials have attracted much attention for use in liquid crystal displays and photovoltaic devices. In particular, Sn-doped In2O3 (ITO) is known as a good transparent conductive oxide material. Recently, ZnO has also been studied as a TCO material because material (Zn) cost is very low in comparison to that of ITO (In). ZnO has shown promise for many applications including gas sensors, transport electrodes, piezoelectric devices, varistors and surface acoustic wave devices. Its direct optical band gap of 3.4 eV at room temperature is wide enough to transmit most of the useful solar radiation in ZnO/CuInSe2 based solar cells. Furthermore, ZnO is a good candidate to substitute for ITO (In-doped In2O3) and FTO (F-doped SnO2) in transparent conductive electrodes. Many techniques have been employed to produce the ZnO thin films including molecular beam epitaxy, metal organic chemical vapour deposition, radio frequency magnetron sputtering, spray pyrolysis and sol-gel methods. In our previous work [1, 2], undoped ZnO films on glass substrates were grown by a spray pyrolysis method at low temperature (RT ~ 300 ˚C). Polycrystalline ZnO thin films were successfully grown at 100 °C under an air atmosphere. Diethylzinc (DEZ) was used as the Zn source material. The DEZ solution was diluted by some solvent in order to use safely under an air atmosphere. X-ray diffraction indicates that (10-10) and (10-11) peaks are dominant. The lattice constants of the a and c axes are larger than those of ICDD data. The samples have c-axis (0002) orientation with increasing substrate temperature. Furthermore, the lattice constants of the a and c axes become closer to those of ICDD data with increasing substrate temperature. In this work, growth of Ga-doped ZnO (GZO) /glass films using DEZ solution was carried out by spray pyrolysis at 150°C. The average transmittance of undoped and GZO films showed 80%. The sheet resistivity of Ga-doped ZnO decreased to 30 /sq. by UV irradiation for 60 min. The sprayed GZO films were examined as TCO layer for Cu(In,Ga)Se2 (CIGS) solar cells. After covering clean soda-lime glass (SLG) substrates with back electrodes of Mo films (0.8 μm) by sputtering, CIGS films (2 μm) were deposited using physical vapor deposition. Buffer layers of CdS films (≈ 50 nm) were prepared by chemical bath deposition. Buffer layers of ZnO films (≈ 80 nm) were also prepared by RF sputtering method [3]. The GZO films were successfully grown on ZnO/CdS/CIGS/Mo/glass by atmospheric spray pyrolysis using DEZ based solution. The efficiency of the obtained device was 10.3%. This result shows the sprayed low resistivity GZO films will be one of the promising candidates for non-vacuum fabricated TCO layer of CIGS solar cell.
References: [1] K. Yoshino, Y. Takemoto, M. Oshima, K. Toyota, K. Inaba, K. Haga, K. Tokudome, Jpn. J. Appl. Phys. 50 (2011) 040207. [2] K. Yoshino, M. Shinmiya, N. Kamiya, J. Kosaka, M. Oshima, Y. Takemoto, K. Toyota, K. Inaba, K. Haga, K.Tokudome, Jpn. J. Appl. Phys. 50 (2011) 108001. [3] T. Minemoto, Y. Hashimoto, T. Satoh, W. S. Kolahi, T. Negami, H. Takakura, Y. Hamakawa., Sol. Energy Mater. Sol. Cells, 75 (2003) 121.
S10-P08 Low Temperature Growth of Ga-doped ZnO Thin Films Grown by Atmospheric Spray Pyrolysis for CuInGaSe2 Based Solar Cells
Kenji Yoshino1,*, Akiko Mochihara1, Himeka Tominaga1, Youei yamaga1, Takashi Minemoto2, Shigeru Ikeda3
1Department of Electrical and Electronic Engineering, University of Miyazaki, 1-1Gakuen Kibanadai-nishi, Miyazaki 889-2192, Japan. 2Department of 1Department of Electrical and Electronic Engineering, Ritsumeikan University, Kusatsu, Japan 3 Research Center for Solar Energy Chemistry, Osaka University, Osaka, Japan *email: [email protected]
Transparent conductive oxide (TCO) materials have attracted much attention for use in liquid crystal displays and photovoltaic devices. In particular, Sn-doped In2O3 (ITO) is known as a good transparent conductive oxide material. Recently, ZnO has also been studied as a TCO material because material (Zn) cost is very low in comparison to that of ITO (In). ZnO has shown promise for many applications including gas sensors, transport electrodes, piezoelectric devices, varistors and surface acoustic wave devices. Its direct optical band gap of 3.4 eV at room temperature is wide enough to transmit most of the useful solar radiation in ZnO/CuInSe2 based solar cells. Furthermore, ZnO is a good candidate to substitute for ITO (In-doped In2O3) and FTO (F-doped SnO2) in transparent conductive electrodes. Many techniques have been employed to produce the ZnO thin films including molecular beam epitaxy, metal organic chemical vapour deposition, radio frequency magnetron sputtering, spray pyrolysis and sol-gel methods. In our previous work [1, 2], undoped ZnO films on glass substrates were grown by a spray pyrolysis method at low temperature (RT ~ 300 ˚C). Polycrystalline ZnO thin films were successfully grown at 100 °C under an air atmosphere. Diethylzinc (DEZ) was used as the Zn source material. The DEZ solution was diluted by some solvent in order to use safely under an air atmosphere. X-ray diffraction indicates that (10-10) and (10-11) peaks are dominant. The lattice constants of the a and c axes are larger than those of ICDD data. The samples have c-axis (0002) orientation with increasing substrate temperature. Furthermore, the lattice constants of the a and c axes become closer to those of ICDD data with increasing substrate temperature. In this work, growth of Ga-doped ZnO (GZO) /glass films using DEZ solution was carried out by spray pyrolysis at 150°C. The average transmittance of undoped and GZO films showed 80%. The sheet resistivity of Ga-doped ZnO decreased to 30 /sq. by UV irradiation for 60 min. The sprayed GZO films were examined as TCO layer for Cu(In,Ga)Se2 (CIGS) solar cells. After covering clean soda-lime glass (SLG) substrates with back electrodes of Mo films (0.8 μm) by sputtering, CIGS films (2 μm) were deposited using physical vapor deposition. Buffer layers of CdS films (≈ 50 nm) were prepared by chemical bath deposition. Buffer layers of ZnO films (≈ 80 nm) were also prepared by RF sputtering method [3]. The GZO films were successfully grown on ZnO/CdS/CIGS/Mo/glass by atmospheric spray pyrolysis using DEZ based solution. The efficiency of the obtained device was 10.3%. This result shows the sprayed low resistivity GZO films will be one of the promising candidates for non-vacuum fabricated TCO layer of CIGS solar cell.
References: [1] K. Yoshino, Y. Takemoto, M. Oshima, K. Toyota, K. Inaba, K. Haga, K. Tokudome, Jpn. J. Appl. Phys. 50 (2011) 040207. [2] K. Yoshino, M. Shinmiya, N. Kamiya, J. Kosaka, M. Oshima, Y. Takemoto, K. Toyota, K. Inaba, K. Haga, K.Tokudome, Jpn. J. Appl. Phys. 50 (2011) 108001. [3] T. Minemoto, Y. Hashimoto, T. Satoh, W. S. Kolahi, T. Negami, H. Takakura, Y. Hamakawa., Sol. Energy Mater. Sol. Cells, 75 (2003) 121.
S10-P10 Nitride-based self-assembled magnetic nanocrystals and complexes
Giulia Capuzzo 1, Thibaut Devillers 1, Andrea Navarro-Quezada1, Mauro Rovezzi2, Tomasz Dietl3, Maciej Sawicki3, and A.Bonanni*1
1Institut für Halbleiter-und-Festkörperphysik, Johannes Kepler University, Altenbergerstrasse 69, A-4040 Linz (Austria) 2European Synchrotron Radiation Facility, 6 rue Jules Horowitz, F-38043 Grenoble (France)
3Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, PL-02-668 Warszawa (Poland) *email: [email protected]
Gallium nitride (GaN) and related alloys as building-blocks for state-of-the-art light emitting diodes and high-power devices have risen to the position of technologically most significant semiconductors next to Silicon. Through the addition of magnetic dopants fostering the formation of active magnetic complexes or driving the system to the state of a condensed magnetic semiconductor, these materials are expected to open striking views in both fundamental and application-oriented research. We summarize our recent work on the fabrication by metalorganic vapor phase epitaxy of magnetic nitrides and highlight how – by exploiting in particular synchrotron radiation and microscopy techniques – we have correlated the growth parameters and protocols to the structural, magnetics, optical properties of the epitaxial layers. We give an overview on how we have unraveled and we can now control by fabrication parameters and co-doping a number of non- anticipated features of these systems, like the self-aggregation and performance of functional magnetic nanocrystals FexN [1-7] and magnetooptically active complexes Mn-Mgk [8,9] embedded in GaN.
The work was supported by the European Reasearch Council (ERC, Project 227690) and by the Austrian Science Foundation (FWF, projects #22477, #24471, #26830).
References: [1] A. Bonanni et al., Phys. Rev. Lett. 101, 135502 (2008). [2]M. Rovezzi et al., Phys. Rev. B 79 , 195209 (2009). [3] A. Navarro-Quezada et al., Phys. Rev. B 81 , 205206 (2010). [4] A. Navarro-Quezada et al., Phys. Rev. B 84 , 155321 (2011). [5] I. A. Kowalik et al., Phys. Rev. B 85 , 184411 (2012). [6] A. Grois et al., Nanotechnology 25 , 395704 (2014). [7] A. Bonanni and T. Dietl, Chem. Soc. Rev. 39, 528 (2010). [8] T.Devillers et al., Scientific Reports 2, 722 (2012). [9] T.Devillers et al., APPL: Phys: Lett. 103, 211909 (2013). [10] T.Devillers et al., Cryst. Growth. Des 15, 587 (2015).
S10-P11 Growth and Formation of Nanostructures on Metal Surfaces under the Action of Nanosecond Laser Pulses
Mikolutskiy Sergey*, Khasaya Radmir, Khomich Yuri, Yamshchikov Vladimir, Zheleznov Yuri
Institute for Electrophysics and Electric Power RAS, 18, Dvortsovaya nab., 191186 St.-Petersburg (Russia) *email: [email protected]
The paper describes the mechanism of nanostructure formation on the metal surface by nanosecond laser radiation. In our work we use one laser beam without any optional devices and masks. Such method is called the direct laser nanostructuring [1,2]. The analysis of irradiated surfaces is carried out by an atomic-force microscope (AFM). AFM-analysis shows that the formation of surface nanostructure occurs in peripheral low intense part of irradiation zone where only a surface melting is observed. For example, figure 1 represents nanostructures obtained on titanium and nickel surfaces as a result of multipulse irradiation by ArF-laser. In order to explain the nanostructure occurrence we offer the theoretical model of nanostructure formation on solid surface by nanosecond laser pulses melting the material [3]. The problem can be divided on two parts. In the first part we consider the process of material melting occurring as a result of laser impact and the Stefan problem with the corresponding boundary conditions is solved. In the second part we consider the process of a melted layer cooling at the expense of heat transmission into the solid phase in combination with a nucleation theory explaining the formation of crystalline seeds. As a result, we obtain the expression for the characteristic size of nanostructures depending on the pulse duration and energy.
(a) (b) Figure 1. AFM images of titanium (a) and nickel (b) surfaces irradiated by ArF-laser
References: [1] Tokarev V.N., Khomich V.Yu., Shmakov V.A., Yamshchikov V.A., Doklady Physics, 53 (2008) 206. [2] Ganin D.V., Mikolutskiy S.I., Tokarev V.N., Khomich V.Yu., Shmakov V.A., Yamshchikov V.A., Quantum Electronics, 44 (2014) 317. [3] Mikolutskiy S.I., Khomich V.Yu., Shmakov V.A., Yamshchikov V.A., Nanotechnologies in Russia, 6 (2011) 733.
S10-P13 The influence of V/III flow ratio on the self-induced InAs nanowires growth
Nickolay V. Sibirev, Umesh Prasad Gomes, Daniele Ercolani, Mauro Gemmi, Vladimir G. Dubrovskii, Fabio Beltram, and Lucia
Sorba
Nanowires (NWs) of III–V semiconductor compounds are promising building blocks for future nanophotonic and nanoelectronic devices and functional photonic circuits. III–V NWs are usually fabricated by various epitaxy techniques via the so-called vapor–liquid–solid mechanism activated by a metal (usually Au) catalyst. Yet, so far catalyst contamination in CMOS technology remains to be challenging. Recently several groups demonstrated NW growth techniques without a catalyst. In this paper we present some arguments to explain highly anisotropic growth of NWs based on the CBE (Chemical Beam Epitaxy) growth of self-induced InAs NWs on silicon. The growth of NWs proceeds in a two stage protocol: low temperature nucleation and high temperature growth steps. InAs NWs were grown in a RIBER C 21 CBE machine on Si (111) substrates. Tertiarybutylarsine (TBA) and trimethylindium (TMI) were used as As and In sources, respectively. TBA was pre-cracked in the injector at 1000 °C. We believe that the low temperature step helps nucleation of NWs, while the high temperature (HT) step is required to start anisotropic growth [2]. Here we present some arguments explaining highly anisotropic growth. First, we suppose that the InAs (111) surface of the NW top facet is likely to exhibit reconstruction with As trimmers on top of the As layer. Thus, the arsenic part of the bilayer should form almost instantaneously and the nucleation would require the completion of only the In layer. Since the nucleation requires the completion of the In layer only, the nucleation barrier is reduced to approximately one half of its value on the side facets. Due to steep exponential dependence of the nucleation rate (and the resulting growth rate) on the nucleation barrier, the axial growth rate will be an order of magnitude higher than the radial one. Much faster growth on the NW top with respect to the side facets also requires diffusion transport of In adatoms to the top. Indium will migrate to the top only if the chemical potential there is lower than at the NW sidewalls [3]. This property is ensured simply by the fact that the top facet is a more efficient sink of In adatoms relative to the side facets and therefore the In concentration on the NW top is the lowest. The concentration gradient gives rise to a diffusion flux to the top. In this sense, the top facet acts as a material collector for In adatoms. Under As-rich conditions, catalyst-free growth of InAs NWs is expected to be limited by surface diffusion of In, similarly to the case of self-induced GaN nanowires under high nitrogen flux [2]. One might argue that the concentration of In adatoms on the NW top is determined by crystallization rate and the latter is determined by the As flux. Yet, the radial growth rate is limited by the In adatoms concentration on the sidewalls which is determined by the difference of impingement flux and diffusion flux to the top. In summary we suppose that in case of self-induced NW growth the axial growth rate of NW is mainly determined by the V-element flux, while the radial growth is controlled by the residue amount of III –element, which cannot be consumed by the axial growth at the NW tip. This effect is partly hidden by the dependence of the pyrolysis efficiency of one III group precursors on the V group precursors pressure.
[1]Ercolani, D.;Rossi,F.; Li, A; Roddaro, S.; Grillo, V.; Salviati, G.; Beltram, F.; Sorba, L. Nanotechnology 2009, 20, 505605. [2] Consonni, V.; Dubrovskii, V.G.; Trampert, A.; Geelhaar, L.; Riechert, H. Phys. Rev. B 2012, 85, 155313. [3] Dubrovskii, V.G.; Sibirev, N.V.; Harmand, J.C.; Glas, F. Phys. Rev. B 2008, 78, 235301.
S10-P14 Growth and characteristics of InAlAs/AlGaAs quantum dots depending on annealing temperatures
Soo Yeon Kim1, Jin-Dong Song1, Il Ki Han*1
1 Center for Opto-Electronic Convergence Systems, Korea Institute of Science & Technology, , Seoul 136-791 (Korea) *email:[email protected]
Semiconductor based quantum dots (QDs) have been attractive because of their promising applications in optoelectronic devices, such as laser diodes, solar cells, and single photon sources [1]. The prospect application of QDs has led to substantial research efforts to grow various kinds of QDs [2]. Recently, light sources with emission wavelength of 808 nm have received attention because of their industrial applications for material process and medical equipment, etc. However, few studies on the material growth for the light sources with the emission wavelength of 808 nm have been reported. Although there have been studied on the growth of InGaAsP/InGaAlAs based quantum wells, the material system suffers from small band offset, resulting in carrier overflows, which is inherent problems of the fabrications for the high-efficiency and high-power light sources. Studies concerning the structural and the optical properties of self-assembled QDs using rapid thermal annealing have been performed to improve the quality of QDs [3]. Among the several types of quantum structures, InAlAs/AlGaAs QDs have emerged as excellent candidates for high- efficiency LEDs because of their high carrier confinement [4]. Even though some studies concerning the formation and the physical properties of InAlAs/AlGaAs QDs have been conducted, few investigations on the influences of growth and annealing temperatures on the structural and the optical properties of the QDs have been performed. In this study, we report data for the effects of growth and annealing temperatures on the structural and optical properties of InAlAs/AlGaAs QDs grown by molecular beam epitaxy. Atomic force microscopy and photoluminescence (PL) measurements were performed to investigate the structural and optical properties of the InAlAs/AlGaAs QDs, respectively. While the (E1-HH1) peak of the PL spectra shifted toward larger energy with increasing up to an annealing temperature of 700 oC, it shifted toward lower energy above 700 oC. PL spectra for the InAlAs/AlGaAs QDs annealed at 700 oC showed that the dominant peak appeared at 818 nm, which approximately corresponded to a 808 light source. This results help to grow InAlAs/AlGaAs QDs for the emission wavelength of 808 nm.
References: [1] D.H. Kim, Y. H. Lee, D.U. Lee, T.W. Kim, S. Kim, and S.W. Kim, Optics Express, 20(2012) 10476. [2] C. Gilfert, V. Ivanov, N. Oehl, M. Yacob, and J.P. Reithmaier, Appl. Phys. Lett., 98(2011) 201102. [3] T. Yokoi, S. Adachi, S. Muto, H. Sasakura, H.Z. Song, S. Hirose, and T. Usuki, Physica E, 29(2005) 510. [4] H.Z. Song, M. Takatsu, H. Sasakura, S. Muto and N. Yokoyama, Phys. Lett. A, 368 (2007) 92.
S10-P15 GaN-ZnO solid solution for photocatalytic applications: Synthesis by Solution Combustion technique and characterization
Sumithra Sivadas Menon1, Anirban Bhattacharyya 2,Somnath Chanda Roy3 ,Bhavana Gupta4, K. Baskar1, Shubra Singh1*
1Crystal Growth Centre,Anna University, Chennai-600025,India 2Institute of Radio Physics and Electronics,University of Calcutta,Kolkatta-700009,India 3Department of Physics, IIT Madras, Chennai-600036, India 4Material Science Group, Indira Gandhi Centre for Atomic Research,Kalpakkam,-603102,India *email: [email protected]
GaN-ZnO solid solution has emerged as a successful and reproducible photocatalyst for overall water splitting by one-step photo excitation, with a band gap in visible region [1]. When the solid solution is formed, some of the Zn and O ions are replaced by Ga and N ions respectively and there is a narrowing of band gap which is hypothesized as due to Zn3d-N2p repulsion. The traditional method of synthesis of GaN-ZnO solid solution is by nitriding the oxides under constant ammonia flow [2].Here we report a solution combustion technique for the synthesis of the solid solution at a temperature below 500oC in a muffle furnace with the nitrates of Ga and Zn as precursors and urea as the fuel. The as prepared samples showed change in color with the increased concentration of ZnO in the solution. The structural, morphological and spectroscopic properties of the samples were realized by Powder X ray diffraction, Scanning electron microscopy, Transmission electron microscopy, Low temperature photoluminescence, Diffuse reflectance spectroscopy, X ray photoelectron spectroscopy, FTIR etc. Thin films of the as prepared samples were coated on ITO substrates by spin coating technique and photoelectrochemical studies were performed. Finally the photocatalytic behavior of the GaN-ZnO nanopowders was found using methanol as a scavenger. The details of the synthesis and characterization will be presented.
(a) (b) Figure. a)Diffuse reflectance spectroscopy of samples with varying Zn to Ga ratio b) Low temperature photoluminescence spectroscopy of GaN-ZnO solid solution.
References: [1] Kazuhiko Maeda., Kazunari Domen., J.Phys.Chem.C, 111(22) (2007) 7851-7861. [2] Kazuhiko Maeda, Tsuyoshi Takata, Michikazu Hara, Nobuo Saito, Yasunobu Inoue, Hisayoshi Kobayashi and Kazunari Domen, J.Am.Chem.Soc, 127(2005) 8286-8287
S10-P16 Cu Catalytic Growth of GaN Nanowires on Sapphire Substrate for p-type behavior Boopathi Kuppulingam*1, Bernard Humbert2and Krishnan Baskar1
1Crystal Growth Centre, Anna University, Chennai-2. (India) 2Institute of Materials, University of Nantes, Nantes.(France) *email: [email protected] Abstract:
The Cu catalytic growth of GaN nanowires (NWs) on c-plane sapphire substrate was investigated using thermal chemical vapor deposition (CVD) process. Impact of reaction temperatures on the crystalline quality has been studied by high resolution x-ray diffraction and Raman spectroscopy and confirmed that the crystalline structure of GaN NWs was wurtzite as shown in Figure 1(a & b). The morphologies of the GaN nanowires were confirmed by scanning electron microscopy. The diameter of NW was about 20-100 nm and length was ~5 µm. Composition and impurities in GaN NWs were studied by EDX analysis. Hall-effect measurement 2 on GaN NWs gives the resistivity (ρ) as 5 Ω cm, hole mobility (µP) as 2.97 cm /V s, hole concentration (p) 4 16 cm-3. Room temperature Photoluminescence (PL) study shows that the near band edge emission for GaN NWs was red shifted to 3.26 eV.
Figure 1. (a) XRD analysis of GaN NWs prepared at various temperatures. (b) The variation of E2(high) mode in Raman spectra of GaN NWs.
References: [1] Wang J C., Zhan C Z., Li F G., Appl Phys A, 76(2003) 609-611.
[2] Yohannes K., Dong-Hau Kuo., Mater sci semicond process, 29 (2015) 288-293. [3] Look D C., Reynolds D C et al., Appl Phys Lett, 81 (2002)1830-1832.
S10-P18 PRECURSORS FOR CIGSe
MICRO-CONCENTRATOR SOLAR CELLS
K. Eylers1*, F. Ringleb1, B. Heidmann2,3, M. Schmid2,3, Ch. Symietz4, J. Bonse4, J. Krüger4, Th. Teubner1, T. Boeck1, and M. Ch. Lux- Steiner3,5
1Leibniz Institute for Crystal Growth, Max-Born-Straße 2, 12489 Berlin, Germany
2Nanooptical Concepts for PV, Helmholtz Zentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany
3Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
4Federal Institute for Materials Research and Testing, Unter den Eichen 44-46, 12203 Berlin, Germany
5Heterogeneous Material Systems, Helmholtz Zentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany
Abstract:
Cu(In,Ga)Se2 (CIGSe) is an excellent absorber for highly efficient thin-film PV applications. However, high costs of raw materials for the preparation of CIGSe are a limiting factor for its industrial competitiveness. An approach to tackle this problem is to reduce material consumption, especially of indium, and increase the cell efficiency by concentrating the incident light onto micrometer-sized CIGSe islands. In contrast to well-established macroscopic concentrator PV, micro-concentrators allow a better heat management and a more compact module design. Furthermore, for a low concentration factor (in the range of 100x), as it is aimed for this project, the requirements on light tracking are relatively low. A promising bottom-up approach for the preparation of ordered CIGSe micro- absorbers is to use indium islands as precursors, which can be grown by PVD in well-defined arrays of nucleation centers that are induced by femtosecond laser pulses on the substrate surface.
S10-P19 Effect of ZnO/B2O3 ratio on the crystal growth in zinc borosilicate glasses
Kullberg Ana Teresa Guerra1, Lopes Andreia Alexandra de Sousa 1, Veiga João Pedro Botelho1, Monteiro Regina da Conceição Corredeira*1
1 Department of Materials Science, CENIMAT/i3N, Faculty of Sciences and Technology, Universidade Nova de Lisboa, Campus da Caparica, 2829-516 Caparica, Portugal *email: [email protected]
Glass samples with a molar composition (64+x) ZnO - (16-x) B2O3- 20 SiO2, where x = 0, 1, were successfully synthesized using a melt-quenching technique with no deterioration of the glass- forming ability. Based on differential thermal analysis data, the produced glass samples were submitted to a controlled heat-treatment at a selected temperature (615C and 620C) during a holding time ranging from 10 to 36 hours. Under these heat-treatment conditions, transparent nanocomposite glass-ceramics were obtained. The crystallization of willemite (Zn2SiO4) within the glass matrix was confirmed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influence of temperature, holding time and ZnO/B2O3 ratio on crystal growth was investigated. The mean crystallite size was determined by applying Scherrer’s equation to the characteristic peak of XRD patterns. These results were compared with those obtained by image analysis on the SEM microstructures. Both methods suggested an increase of the crystallite size with time, temperature and ZnO/B2O3 ratio. Further investigation will be related to the optical characterization of the produced transparent nanocomposite glass-ceramics regarding their potential applications in photonics.
Acknowledgements: To FCT (Foundation for Science and Technology) Portugal, for financing M- ERA.NET/0010/2012 and UID/CTM/500025/2013.projects.
S10-P20 Synthesis and Characterization of HgI2 Nanostructures for Films Nucleation
Pérez Barthaburu María 1*, Galain Isabel2, Olivera Alvaro1, Bentos Pereira Heinkel1, Fornaro Laura1
1Grupo de Desarrollo de Materiales y Estudios Ambientales, Departamento de Desarrollo Tecnológico, CURE, Universidad de la República, Ruta 8 and Ruta 15, Rocha, Uruguay 2Grupo de Desarrollo de Materiales y Estudios Ambientales, Cátedra de Radioquímica, Facultad de Química, Universidad de la República, General Flores 2124, Montevideo, Uruguay *email: [email protected]
With the aim of controlling the first steps in HgI2 film growth onto amorphous substrates, we studied the synthesis of HgI2 nanostructures. Nanostructures were obtained by two different synthesis methods. In one procedure HgI2 was obtained from Hg(NO3)2 and I2 in ODE at a constant temperature of 70 ºC. The synthesis time was varied between 0 and 4 hours. In other procedure Hg(NO3)2, KI or NaI were used for obtaining HgI2 in water. Samples were then subjected to an hydrothermal treatment at a constant temperature during 2, 10, 19 and 24 hours. All samples were centrifuged and dried in a laboratory oven. Both aforementioned methods are facile for obtaining HgI2 nanostructures and easily scalable. HgI2 tetragonal phase was confirmed by powder X-ray diffraction. Nanostructures were characterized in their morphology by transmission electron microscopy and in their size also by the Scherrer method when possible. We observed that nanostructures obtained in ODE were more stable against the electron beam while the ones subjected to the hydrothermal treatment were more labile, sublimating/evaporating completely during observation. In between samples obtained in ODE at different synthesis times, the one performed during 4 hours yielded the best results in terms of morphology and size distribution. Crystalline round nanostructures between 2 and 40 nm in size inserted in elongated structures were observed in the former sample. TEM images of samples synthesized in ODE and with hydrothermal treatment can be seen in Figure 1. HgI2 nanostructures were used as nuclei for nucleation onto amorphous substrates. They were deposited onto ITO coated and uncoated flat silica glass by spin coating. The morphology of this mechanical nucleation was studied by atomic force microscopy. Further film growth was performed onto the nucleations by the physical vapor deposition method to study nucleation influence. This mechanism of HgI2 nucleation is very promising for improving the film growth orientation and therefore the current applications of this material, as far as for opening new ones.
Figure 1. HgI2 nanostructures: a- synthesized in ODE. b- after hydrothermal treatment
S10-P21 Synthesis and investigation of hexagonal modification NaY1-x-yYbxEryF4
Mayakova Mariya*1, Fedorov Pavel1, Kuznetsov Sergey1, Voronov Valerii1, Pominova Daria1, Ryabova Anastasia1, Baranchikov Alexander2
1Prokhorov General Physics Institute, Russian Academy of Sciences, 119991, Vavilov Str., 38, Moscow (Russia) 2Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 119991, Leninsky prospect 31, Moscow (Russia) *email: [email protected]
Interest in synthesis and study of fluoride powders is rapidly increased recently. An unique set of physical and chemical properties of fluorides cause the possibility of using fluoride powders in various fields of science and technology. Fluoride powders can be used as the precursors for laser ceramics and single crystals preparation, for different biomedical applications. NaYF4 is one of the most efficient phosphors. NaYF4 crystallizes in two polymorphic modifications: the high-temperature cubic (fluorite structure type) and low-temperature hexagonal (gagarinite structural type). According to the literature data, erbium and ytterbium doped low- temperature hexagonal modification is high efficiency up-conversion matrix. There are many methods for the synthesis of low-temperature modification NaYF4, but most of them involve technical difficulties. In this paper we used the method of spontaneous crystallization from the melt for the synthesis of NaYF4 and NaY1-x-yYbxEryF4 (x, y = 1 ÷ 10 mol.%) hexagonal modification. The optimal synthesis conditions (temperature synthesis, the amount of solvent, the excess of the fluorinating agent, additional heat treatment conditions) were determined. Single-phase solid solutions with the gagarinite structure confirmed by x-ray diffraction were synthesized. The morphology of the synthesized powders was studied by scanning electron microscopy (figure 1). Large particles are hexagonal morphology hollow inside, and the outer walls have a thickness about 50 nm. Ytterbium and erbium doped synthesized NaYF4 samples showed high values of the energy yield of up-conversion luminescence.
Figure 1. Scanning electron microscopy image of the powder NaYF4
S10-P22 Hydrothermally Grown Arrays of ZnO Nanorods on Patterned Substrates
Jan Grym1*, Roman Yatskiv1, Jan Vaniš1, Jiří Slabý 1, Jaroslav Maixner2
1Institute of Photonics and Electronics CAS, Chaberská 57, Prague 8 (Czech Republic) 2Central Laboratories, Institute of Chemical Technology, Technická 5, Prague 6 (Czech Republic) *email: [email protected]
Semiconductor one-dimensional (1D) nanostructures possess a vast number of remarkable physical and chemical properties thanks to their high aspect ratio at nanoscale dimensions. ZnO is a direct wide bandgap semiconductor crystallizing in the wurtzite structure with a series of unique properties: a large exciton binding energy, which inhibits thermal activation and enhances light emission at room temperature; good optical transmittance in the visible region; high optical gain; piezoelectricity; room temperature ferromagnetism; mechanical stability given by the high melting point and large cohesive energy; radiation hardness; or biological compatibility [1]. These properties allow for applications of ZnO in UV light-emitting devices and detectors, field-effect transistors, solar cells, piezoelectric nanogenerators, or chemical sensors [2]. For the majority of these applications, upright standing arrays with controlled positioning, sizes, and physical properties are preferred over the free standing 1D nanostructures, which require additional manipulation. The upright standing arrays were prepared by hydrothermal growth on Si substrates with a ZnO seed layer and on GaN epilayers patterned by e-beam lithography (fig. 1) or by focused ion beams. Electrical contacts were formed by a variety of techniques (see schematics in fig. 2) to study the electrical charge transport. The transport properties were correlated with the structural and optical properties investigated by x-ray diffraction and photoluminescence spectroscopy.
Figure 1. Example of the array of ZnO 1D Figure 2. Schematics of different techniques to characterize electrical structures grown on GaN substrate patterned properties of ZnO 1D structures and their arrays. by e-beam lithography.
This work has been supported by the Czech Science Foundation project 15-17044S and by the EU COST Action TD1105 – project LD14111.
References: [1] Ahmad M., Zhu J., Journal of Materials Chemistry 21/3 (2011) 599-614. [2] Xu S., Wang Z.L., Nano Research 4/11 (2011) 1013-1098.
S10-P23 Synthesis of BiI3 nanoparticles through hydrothermal method intended for preparing ionizing radiation detectors
Aguiar Ivana1*, Mombrú Maia1, Pérez Barthaburu María2, Fornaro Laura2
1Grupo de Desarrollo de Materiales y Estudios Ambientales, Cátedra de Radioquímica, Facultad de Química, Universidad de la República, Av. General Flores 2124, Montevideo (Uruguay) 2Grupo de Desarrollo de Materiales y Estudios Ambientales, Departamento de Desarrollo Tecnológico, Centro Universitario Regional del Este, Universidad de la República, Ruta 9 and Ruta 15, Rocha (Uruguay) *email: [email protected]
Compound semiconductors of heavy metal iodides such as BiI3 have been widely studied due to their properties as materials for room temperature gamma and X-ray detectors, such as high atomic number of their elements, high density and high atomic absorption, which means high counting efficiency [1]. Recently, nanostructures of these compounds are being synthesized due to their capacity of being pressed into pellets, which comprises a new way of constructing detectors much simpler than the crystal growth. The hydrothermal method with selective precipitation was chosen as a suitable route for obtaining BiI3 nanoparticles. BiCl3 and NaI were used as precursors and oxalic acid was used as capping agent to study its influence in size and morphology. The nanoparticles were characterized by XRD, FTIR and TEM. Nanoparticles with oxalic acid of the first precipitation range 9-10nm in diameter with round morphology. The same morphology was observed in the second precipitation, however slightly smaller in size, 6-7 nm in diameter (Figure 1). The characterizations performed to BiI3 synthesized without capping agent proved that the desired product is obtained as well, but with particles with a size about 20 nm. Pellets were fabricated with the nanoparticles and detectors were constructed with them. The particles reported here have better uniformity in size than the ones obtained in solution [2], showing that the addition of oxalic acid improves the properties of the final particles. The detectors showed resistivities of 1010-1011 Ω.cm and respond to a 241Am source. These preliminary electrical and response to radiation studies performed to detectors are promising, and encourage us to deep into the development of this kind of detectors.
Figure 1. BiI3 nanoparticle obtained through hydrothermal synthesis with oxalic acid as capping agent.
References:
[1] M. Overdick, C. Baumer, K.J. Engel, J. Fink, C. Herrmann, H. Kruger, M. Simon, R. Steadman, G. Zeitler, IEEE Trans. Nucl. Sci (2009) 56, 1800-1809. [2] L. Fornaro, I. Aguiar, M. Pérez Barthaburu, A. Olivera, I. Galain, M. Mombrú, J. Cryst. Growth, 401 (2014) 489-493.
S10-P24 HgS nanostructures for the development of hybrid active layers
Galain Isabel*1, Pérez Barthaburu María2, Aguiar Ivana1, Fornaro Laura2
1Grupo de Desarrollo de Materiales y Estudios Ambientales, Cátedra de Radioquímica, Facultad de Química, Universidad de la República, Av. General Flores 2124, Montevideo (Uruguay) 2Grupo de Desarrollo de Materiales y Estudios Ambientales, Departamento de Desarrollo Tecnológico, Centro Universitario Regional del Este, Universidad de la República, Ruta 9 and Ruta 15, Rocha (Uruguay) *email: [email protected]
In recent years the use of semiconductor nanoparticles in nanostructured solar cells and hybrid organic-inorganic solar cell has increased. The incorporation of inorganic nanostructures as electron acceptors provides advantages to the solar cells performance, for example, by altering the cells absorption profile [1-2]. For this reason, we synthesized HgS nanostructures by the hydrothermal method in order to use them in hybrid organic-inorganic solar cells. We employed different mercury sources (HgO and Hg(CH3COO)2) and polyvinylpyrrolidone (PVP) or hexadecanethiol (HDT) as capping/stabilizing agents for controlling size, crystallinity, morphology and stability of the obtained nanostructures. We also used thiourea as sulfur source, and a temperature of 180ºC during 6 h. Synthesized nanostructures were characterized by powder x-ray diffraction, diffuse reflectance infrared Fourier Transform, transmission electron microscopy, and electron diffraction. When PVP acts as stabilizing agent, the mercury source has influence on the size of the beta- HgS nansostructures obtained, but not in their morphology. HDT has control over nanostructures´size and depending on the relation Hg:HDT, we obtained a mixture of alpha and beta HgS which can be advantageous in its application in solar cells due to absorption in different spectral regions. The smallest obtained nanostructures have an average diameter of 20 nm when using HDT as capping agent, as can be seen in Figure 1. Results obtained are very promising and represent important advances for the improvement of hybrid solar cells.
Nanostructure size distribution 50 45 40 35 30 25 20 Frequency 15 10 5 0 5 101520253035404550 Particle Feret's diameter (nm) Figure 1.TEM Image of HgS nanostructures obtained with HDT as capping agent.
References: [1] Wright M., Uddin A., Solar Energy Materials & Solar Cells 107, 107 (2012) 87-111. [2] Higginson K. A., Kuno M., Bonevich J., Qadri S. B., Yousuf M., Mattoussi H., J. Phys. Chem. B, 106 (2002) 9982-9985.
S10-P25 Growth of ZnO nanorods on carbon fibers for in-situ stress measurements Culiolo Maurizio*1, Delmonte Davide1, Villani Marco1, Marchini Laura2, Bercella Rocco2, Calestani Davide1, Coppedè Nicola1, Solzi Massimo3, Zappettini Andrea1 1IMEM-CNR, Parco Area delle Scienze 37/A, 43124 Parma (Italy) 2Bercella s.r.l., via Enzo Ferrari 10, 43040 Varano de’ Melegari (PR), (Italy) 3Dipartimento di Fisica e Scienze della Terra “Macedonio Melloni” – Università degli Studi di Parma, Parco Area delle Scienze 7/A, 43124 Parma (Italy) *email: [email protected] Carbon fiber based composites (CFC), owing to the exceptional ratio between mechanical properties and weight, represent a fundamental technology for several applications, ranging from aerospace to automotive, from civil infrastructure to biomedical engineering. Due to the intense mechanical stress often involved, strain and deformation on CFC made structures have to be constantly monitored. Furthermore univocal mechanical models doesn’t exist, since carbon fiber (CF) patches can be textured with CF oriented in different directions depending on necessity. Nowadays strain sensing on CFC is carried out with optical fiber and piezoelectric ceramics. However this technologies present three main drawbacks, that are large size (compared to CF size), weight addition to the structure and use of precious metals wires. Recently the use of different materials functionalized with piezoelectric zinc oxide (ZnO) nanostructures started to get a foothold for sensing and energy harvesting. Piezoelectric effect, owing to its dual peculiarity relating deformation with electric properties, lends itself to both sensing and actuating applications. Therefore functionalization of CF with ZnO piezoelectric nanostructures allow to realize a fully integrated piezoelectric sensor/actuator within CFC structure, thanks also to the fact that conductive CF themselves act as electrical wires. The ZnO in-situ growth is made by a low-temperature and low-cost two-step process: functionalization of CF with ZnO seed-layer by Successive Ionic Layer Adsorption and Reaction (SILAR) technique and growth of ZnO nanorods by chemical bath deposition. Measuring the piezoelectric effect in ZnO nanostructures is still a debatable topic, since the typical I-V characterization is not generally accepted. In this work piezoelectric investigation is carried out for the first time on such structure using ferroelectric virtual ground, PUND and DHM techniques. The emergence of a voltage-invariant capacitance variation upon stress application is ascribed as the fingerprint of piezoelectricity.
Figure 2. Depiction of the device structure: crossed CF functionalized with ZnO seed-layer and nanorods.
S10-P27 High-Density n-ZnSe Nanowires Grown on CdS/ITO Glass for Hydrogen Evolution
by Dual Visible Light Absorption
Ki-Hyun Cho, Kyung-Shik Kim, Jong Yeon Choi, and Yun-Mo Sung Department of Materials Science & Engineering, Korea University, Seoul 136-713, South Korea
For the first time ZnSe nanowires were successfully grown on a substrate by a low-temperature solution method. Bi catalysts were used for the solution-liquid-solid (SLS) growth of ZnSe nanowires. They were highly crystalline and in zinc blende structure. Their average diameter and length were ~30 nm and ~2-3 m, respectively. There exist only a few papers reporting the application of ZnSe for water splitting. The role of ZnSe (~2.7 eV) was only sensitizing TiO2 having wide band gap (~3.2 eV) under visible light illumination.
In this study we demonstrate the combination of n-ZnSe and n-CdS for the construction of effective Z-scheme water splitting. Both ZnSe and CdS (energy band gap of ~2.5 eV) can be activated under visible light. At the thermal equilibrium, to meet the Fermi energy level the energy bands of ZnSe sift down to positive potential and those of CdS shift up to the negative potential. As a result, we could obtain a higher reduction (electron) potential from CdS and a higher oxidation (hole) potential from ZnSe, and in turn Z-scheme could be completed between ZnSe and CdS. The excited electrons in CdS can move to a Pt electrode and reduce hydrogen ions to evolve hydrogen gas, while the excited electrons in ZnSe can combine with holes in CdS at the ZnSe/CdS interface, eliminating the photocorrosion problem of CdS. The holes in ZnSe can oxidize water to evolve oxygen gas.
The excited electrons from CdS layer could transfer to the Pt electrode through ITO substrates and the photocurrent density was measured to be ~2.9 mA/cm2 at 0 bias voltage under visible light irradiation. This photocurrent value is an almost two times higher value than that from only n-ZnSe nanowire anodes. This increased photocurrent density could originate from the effective electron and hole separation of ZnSe by the formation of Z-scheme and increased reduction and oxidation potentials by energy band aligning between ZnSe and CdS.
This paper demonstrates the first successful growth of ZnSe nanowires on a substrate by a solution method and the first try of using ZnSe as a hole carrier for the Z-scheme water splitting. Large-area n-ZnSe/n-CdS photoanodes can be achieved using the low-temperature SLS growth.
S10-P29 Mass-transport driven growth dynamics of AlGaAs shells deposited by metalorganic vapor phase epitaxy around dense GaAs nanowire ensembles
Ilio Miccoli1, Paola Prete2, Nico Lovergine*1
1Dip. di Ingegneria dell’Innovazione, Università del Salento, I-73100 Lecce, Italy 2Istituto per la Microelettronica e Microsistemi, CNR, UOS Lecce, I-73100 Lecce, Italy *email: [email protected]
III-V compounds nanowires are expected to impact several device technology fields, ranging from nanoelectronics, to nanophotonics, and photovoltaics, by offering both unprecedented materials properties and novel device geometries/functionalities. Radial modulation of nanowire composition and/or doping in the form of core-shell and core-multishell nanowire heterostructures has been proposed for novel nano-LEDs/-lasers [1,2]. In order to exploit MOVPE technology for the fabrication of such devices, good control over the growth process of radially-heterostructured nanowires is necessary. While many efforts have been devoted in understanding/modelling the Au- catalysed (VLS) growth of III-V nanowires, much less is known on the growth dynamics of shell materials by the conventional (Vapor-Solid) MOVPE around free-standing core nanowires. We report on a detailed experimental analysis of AlGaAs shell growth by MOVPE around free- standing GaAs nanowires, the latter self-assembled by the Au-catalyzed process on (111)B-GaAs wafers or GaAs/(111)Si hetero-substrates [3]. We demonstrate that the vapour mass-transport supply of III-group species during shell growth couples with the nanowire size (e.g. their diameter) and their local surface density on the substrate to determine the actual shell growth rate. A vapor mass-transport model is proposed and validated, describing the MOVPE growth dynamics of the shell material around dense ensembles of GaAs nanowires [4]. We predict a complex (non-linear) dependence of the shell growth rate on initial GaAs nanowire diameters, heights, local densities on the substrate, and deposition time (see Figure 1). Present results constitute a significant step towards the controlled fabrication of core-shell and core-multishell nanowire heterostructures by MOVPE.
(a) (b)
Figure 1: Average diameter of GaAs-AlGaAs core-shell nanowires as function of (a) their substrate surface density (NW) after 10 min shell growth, and (b) the shell growth time for different NW.
References: [5] B. Mayer, D. Rudolph, J. Schnell, S. Morkotter, J. Winnerl, J. Treu, K. Muller, G. Bracher, G. Abstreiter, G. Koblmuller, Nat. Comm. 4 (2013) 2931. [6] K. Tomioka, J. Motohisa, S. Hara, K. Hiruma, T. Fukui, Nano Lett. 10 (2010) 1639. [7] I. Miccoli, P. Prete, F. Marzo, D. Cannoletta, N. Lovergine, Cryst. Res. Technol. 46 (2011) 795. [8] I. Miccoli, P. Prete, N. Lovergine, submitted (2015).
S10-P30 Laser processed oxides for optoelectronics and bio applications
Soares Rosa1, Rodrigues Joana1,Santos Nuno1, Holz Tiago1, Ferreira Nuno1, Sousa Marta1,Ferro Marta2 Fernandes António1, Cunha António1, Monteiro Teresa 1, Costa Florinda*1
1Departamento de Física & I3N, Universidade de Aveiro 3810-193, Aveiro (Portugal) 2Depart. de Eng. de Materiais e Cerâmica & CICECO, Universidade de Aveiro 3810-193, Aveiro (Portugal) *email: [email protected]
Laser processing is known as one of the most ultimate techniques in light based manufacturing to develop technological devices. Additionally, the use of high power lasers constitutes nowadays an alternative methodology to the chemical routes in the materials synthesis/growth. Bulk crystals, thin films and nanoparticles/nanostructures are currently achieved by laser processing techniques. In this work, light emitters based on lanthanide ions (Ln3+) doped zirconia system were grown as singe crystals and nanoparticles (NPs). Laser floating zone (LFZ) [1] technique was explored to grow high quality single crystals while NPs were produced by the pulsed laser ablation in liquid (PLAL) [2]. PLAL process was used to produced Tb 3+ and Eu 3+ doped yttria stabilized zirconia (YSZ) NPs in water (figure 1), for application in biolabeling and bio-imaging based in time resolved (TR) luminescence detection. Moreover, YSZ NPs with upconversion (UC) luminescence, with enhanced prospects as luminescent source in bio-imaging, such as the ones co-doped with Tm3+ and Yb3+ ions were also produced by PLAL. Additionally, wide band gap semiconductors such as ZnO and SnO2 with high structural and optical quality were grown as micro and nanocrystals with distinct morphologies by the laser assisted flow deposition (LAFD) method. This technique allows the synthesis of materials having close melting and evaporation points with controllable morphology by an adequate choice of the growth parameters [3,4]. The use of the LAFD technique to grow functional ZnO nanostructures (nanoparticles and tetrapods) working as nano templates for different approaches, namely as dye- sensitized solar cells (DSSCs) [5], will be highlighted. a) b) Energy (eV) 4.5 4 3.5 3 2.5 2 1.4 5 7 YSZ: 1% Tb colloid D4 F5 1.2 RT
1.0
0.8 4 3 F F 7 5 7 5 7 7
0.6 D F D F 4 6 3 6 4 x 20 4 D
5 7 D 5 5 5 7 D3 F5-2 0.4 D4 F2
0.2 PL: 277 nm Normalized Intensity Intensity Normalized x 80 0.0 PLE @ 544 nm
250 300 350 400 450 500 550 600 650 700 750 800 Wavelength (nm) Figure 1. a) TEM images and b) RT PL and PLE of the YSZ:Tb NPs produced by PLAL
References: [1] M.R.N. Soares et al., J. Appl. Phys.,109 (2011) 013516. [2] M.R.N. Soares et al., RSC Adv., 5 (2015) 20138 [3] J. Rodrigues et al., Proc. SPIE, SPIE OPTO, (2015) 89871F [4] N. F. Santos et al., Phys. Chem. Chem. Phys., 17 (2015) 13512-13519 [5] J. Rodrigues et al., submitted (2015)
S10-P31 Obtaining of II-VI compound single crystal substrates with controlled electrical properties and prospects of their application for manufacturing nanotemplates
Colibaba Gleb* 1,2, Monaico Eduard3, Tiginyanu Ion3, Goncearenco Evgenii1, Inculet Ion1
1Moldova State University, A. Mateevici 60, MD-2009, Chisinau, Moldova
2Kazan Federal University, Kremlevskaya 18, 420008, Kazan, RF 3 Technical University of Moldova, Stefan cel Mare 168, MD-2004, Chisinau, Moldova *email: [email protected]
Wide band-gap II-VI semiconductors are perspective materials for the fabrication of nanoporous matrices (NM) or nanotemplates. The conductive semiconductor nanotemplates possess wide potential for the growth of networks of nanowires, nanotubes and nanodots based on various materials. These nanostructures are promising for use in high-efficient solar cells with nanostructured p-n junctions, photonic elements, electronic sensors etc. The easiest and cost-effective method to obtain NM is electro-chemical etching (ECE), which, however, depends on conductive properties of the substrates. The conditions of growing homogenious ZnSe and ZnS single crystals by physical vapour transport method, and also CdS, ZnSSe, ZnCdS and ZnO single crystals by chemical vapour transport method based on HCl vapors are discussed. Based on the results of investigation of electrical properties of the samples with various doping levels, the prospect of examined technology for manufacturing the substrates of these compounds with large area and controlled n-type electrical conductivity varried up to 20, 0.3, 100, 0.3, 30, and 20 (Ω·cm)-1, respectively, is estimated. The results of nanostructuring II-VI compound substrates using various acid electrolytes are shown. The prospect of using ZnSe and ZnCdS compounds for obtaining nanopore arrays with pore diameter down to 30 nm and pore depth up to 1 mm, as well as ZnO substrates for nanohills or nanopits arrays, are demonstrated. The limitations for producing the similar structures on the basis of ZnS and ZnSSe substrates, and features of etching polar ZnO substrates are shown.
Figure. Scanning electron microscope image in cross-section of porous Zn0.5Cd0.5S layer (a), Zn0.6Cd0.4S multilayer (b); Oxide face of ZnO substrates anodized in K2Cr2O7:H2SO4:H2O electrolyte (c), HNO3:H2O electrolyte (d), HCl:H2O electrolyte (e) and Zn face of ZnO substrates anodized in HCl:H2O electrolyte (f).
This work was supported by the Moldavian National grant No.14.819.02.14A, and partially by the Russian Government (agreement No.02.A03.21.0002) to support the Program of Competitive Growth of Kazan Federal University among World’s Leading Academic Centers.
S10-P32 Surface Morphological Analysis of nano-patterned c-plane sapphire substrates using 450KeV oxygen ions I. Davis Jacob1, G.K.Priya Merline1, K. Asokan2, K. Baskar1 and M. Chitra1*
1Crystal Growth Centre, Anna University, Chennai (India) 2Inter University Acceleration Centre, New Delhi (India) *email for correspondence: [email protected], [email protected]
Abstract: Nano-patterning using implantation of 450KeV oxygen ions on the sapphire substrates causes restructuring and creates nucleation centres on the surface of c-cut sapphire wafers that has a direct impact on the growth kinetics in the Two-step nucleation and MOCVD growth of the GaN buffer layers and the dislocation density arising due to the lattice mismatch between the sapphire and GaN layers. In this study, the c-cut wafers of sapphire are annealed at 1350°C for about 12 hours. Annealing widens the terraces on the c-cut (0001) plane of sapphire where steps are clearly visible indicating a miscut angle during the chemo-mechanical polishing of sapphire wafers. Annealing improves the crystallinity of sapphire. Implantation of 450KeV oxygen ions were carried out in the fluence range of 5x1011 ions/cm2 to 1x1014 ions/cm2. AFM analysis reveals that low fluence implantation of oxygen causes horizontal streaks of damage in the crystallinity on the c-cut surface whereas higher fluence implantation of oxygen causes tiny hillocks of crystal damage.
S10-P33 Surface modification of Cu2O/p-CuxS thin films for Liquefied Petroleum Gas sensing
Bandara Nayana Dammika a,b,Jayathileka Charith a,d, Gunewardene Siyath a, Dissanayake Dhammike.c, Jayanetti Sumedhaa,* a Department of Physics, University of Colombo, Colombo 03, Sri Lanka b Department of Physics, Open University of Sri Lanka, Nawala, Nugegoda, Sri Lanka c Department of Chemistry, University of Colombo, Colombo 03. Sri Lanka d Department of Physics, University of Kelaniya, Kelaniya, Sri Lanka *referring author E-Mail: [email protected] Liquefied petroleum (LP) gas is widely used, for domestic, commercial and industrial purposes around the world. It is an extremely inflammable hazardous gas. Efficient sensing of unsafe levels of LP gas will help to minimize the risks of accidents. This work focuses on a novel mechanism to detect LP gas effectively using electrochemically deposited n-type cuprous oxide thin films on Ti substrates in acetate bath with surface modification through sulphidation followed by passivation, which forms a thin film n-Cu2O/p-CuxS semiconducting heterostructure. Detection can be achieved at operating temperatures <100ºC and is a relatively simple and low cost technique. In order to fabricate n-Cu2O/p-CuxS heterostructures, electrochemically deposited n-type cuprous oxide (n-Cu2O) thin films on Ti substrates in acetate bath were sulphided using Na2S. Subsequently these thin film structures were passivated using (NH4)2S vapor. As a result of passivation, the sensitivity (fractional change in thin film resistance) of thin films were enhanced when exposed to liquefied petroleum (LP) gas at 45ºC with quick response and recovery characteristics. The scanning electron microscopy (SEM) showed that the unsulphided n-type Cu2O thin films exhibited typical polycrystalline surface morphology, while SEM of sulphided and passivated thin films revealed micro/nano crystalline surface morphological features with porous structures(Figure 1). As expected, the thin film structures obtained through sulphidation followed by passivation of n-type Cu2O films decreased the film resistance (1 kΩ) in comparison to the resistance (1 MΩ) of the unsulphided n-type Cu2O thin films. Upon exposure to LP gas, the resistance of these thin film structures increased while sensitivity to LP gas depended on the electrochemical deposition time, the passivation time and the sensing temperature. The crucial factor for the recovery of the resistance to its ambient resistance when the exposure of sulphided and passivated thin film structures to LP gas was stopped, was an optimal n- type Cu2O thin film thickness. The highest sensitivity of 48 %.was recorded when the exposure of thin film structures fabricated by electrodepositing n-type Cu2O thin films for 45 min., sulphided and passivated for 5 s and maintained at a sensing temperature of 45 ºC to LP gas.(Figure 2)
1μm
Figure 1. SEM picture of sulphided and passivated Figure 2. Sensitivity variations of sulphided and passivated Cu2 O thin films Cu2 O thin films with the exposure of LP gas
SESSION 11
Novel Materials and Structures
In-situ observations of the catalytic growth of nanomaterials
Stephan Hofmann
Department of Engineering, University of Cambridge, United Kingdom *email: [email protected] With a focus on diverse applications in the electronics and display industry, we aim at developing integrated process technology for nanomaterials, like semiconducting nanowires. In order to go beyond empirical process calibrations, we systematically use in-situ metrology to reveal the mechanisms that govern the growth, interfaces and device behaviour of these nanomaterials in realistic process environments. This talk will focus on recent results for Si and Ge nanowires with a particular emphasis on fundamental aspects and the use of these structures as model systems to explore more generic aspects of phase behaviour, nucleation and interface dynamics in nanoscale systems. Video-rate lattice-resolved environmental transmission electron microscopy (ETEM) of Au catalyzed Ge nanowire (Ge NW) growth allows us to directly observe the formation of metastable AuGe phases without quenching [1]. We rationalise the unexpected formation of these phases through a novel pathway involving changes in composition rather than temperature. ETEM of Ge NW growth also allows us to directly observe twin-mediated crystal growth. In contrast to the classic twin plane re-entrant mechanism (TPRE) for bulk crystals, we find that the nanowire geometry allows steady-state growth with a single twin boundary at the nanowire center [2]. Our data allows us to focus on why a single twin leads to growth and to consistently interpret prior NW literature, for example, reporting post-growth data of preferential impurity incorporation along twin defects and the frequent observation of twins in NWs growing in the 112 direction. We propose that the nucleation barrier at the twin plane re-entrant groove is reduced by the presence of a line energy. Our results are of general validity and provide an important insight into the TPRE growth process of bulk materials. Forming reliable contacts is crucial in particular for nano-scale electronic devices. We show that nanowires offer an ideal platform to study contact formation with ETEM allowing a record of atomically resolved interface formation. We report on a new form of epitaxy that involves silicide phase formation via the catalyst particle and offers a generic platform for seeding new crystals and forming heterostructures (see Figure)[3].
Figure 1. In-situ TEM images showing the formation and incorporation of a nickel silicide (NiSi2) nanoparticle (colored yellow) into a silicon nanowire during catalytic growth [3].
References: [1] Gamalski et al., Phys. Rev. Lett. 108, 255702 (2012). [2] Gamalski et al., Nano Lett. 14, 1288 (2014). [3] Panciera et al., Nature Materials, DOI: 10.1038/NMAT4352 (2015).
Crystal engineering of molecular solids: "light" interactions for interactions with light. Fabrizia Grepioni,a Simone d'Agostino,a Dario Braga,a Barbara Ventura,b Mirko Serib aDipartimento di Chimica G. Ciamician, via Selmi, 2 - 40126 Bologna bIstituto ISOF-CNR, Via P. Gobetti, 101, 40219 Bologna, Italy.
Molecular crystal engineering, i.e. the design and synthesis of solid state molecular materials with predefined properties, is used here to exploit non-covalent interactions to pre-arrange buiding blocks in their crystalline state for properties modification and specific applications, all involving the absorption of UV radiation.
Depending on the chemical complexity and/or application, crystals of appropriate size and purity are required for characterization, chemical reactivity and applicative processes. Three cases will briefly be presented here: (i) single crystal to single crystal photodimerization of cinnamic acid derivatives and the effect of crystal size on the solid-state reactivity; (ii) co- crystallization as a tool to switch from fluorescence to phosphorescence in the solid state, and the necessity of obtaining single crystals following a mechanochemical synthesis; (iii) molecular crystals for dye-sensitized solar cells applications, and the single crystal vs. polycrystalline material requirements on passing from characterization to photophysical measurements and to thin-film deposition.
Chemical Vapor Transport towards new geo-inspired selenite based materials.
Marie Colmont*1, Vadim M. Kovrugin1,2, Oleg I. Siidra2, Sergey V. Krivovichev2 and Olivier Mentré1
1Université Lille 1 Sciences et Technologies, UMR 8181 CNRS, Unité de Catalyse et Chimie du Solide ‘UCCS’, F-59655 Villeneuve d’Ascq, France 2Department of Crystallography, St. Petersburg State University, University Emb. 7/9, 199034 St. Petersburg, Russia
The demand for new noncentrosymmetric compounds is very strong because of their possible interesting properties such as second-harmonic generation (SHG), piezoelectricity, ferroelectricity or pyroelectricity. Particularly, Se4+ cation is of huge interest because of its stereoactive lone pair of electrons usually assorted to asymmetric coordination environments. The crystal chemistry of metal selenites is very rich and if cleverly used with other cations as Pb2+ or Bi3+, chances to get asymmetric building units or NCS crystal structures are highly enhanced. From an experimental point of view, CVT synthesis is a technique of choice because (1) of the high volatility of SeO2, BiCl3 or PbCl2 used as precursors, (2) it is less used as other common synthesis process giving more chances to get new crystal structures and (3) it provides a good opportunity to simulate conditions in fumarolic environments in favor of stabilization of selenite phases. In this presentation, after reminding experimental key parameters of CVT synthesis, the investigation of three different systems (1) cоpper1, (2) lead2 and (3) bismuth chloroselenites3 will be presented, including new crystal structures. Results from the cоpper system are shown in Figure 1. Crystals of K[Cu5O2](SeO3)2Cl3 were isolated in the source zone. The isotypic structure was also obtained with Na instead of K and are related to the known mineral, ilinskite.
Figure 1. General scheme of the CVT method (a), the source zone of the tube (b), the crystals of K[Cu5O2](SeO3)2Cl3 picked out from the source zone (c), and a common view of the sealed silica tube after the CVT synthesis (d)
The authors sincerely thank the ANR (grant ANR-12-JS08-0012) for financial support.
References: [1] V. M. Kovrugin, O. I. Siidra, M. Colmont, O. Mentré, S. V. Krivovichev, Mineralogy and Petrology, 2015, DOI: 10.1007/s00710-015-0369-3 [2] V. M. Kovrugin, M. Colmont, O. I. Siidra, S. V. Krivovichev, O. Mentré, Crystal Growth and Design, submitted [3] Aliev, V.M. Kovrugin, M. Colmont, C. Terryn, M. Huvé, O.I. Siidra, S.V. Krivovichev, O. Mentré, Crystal Growth and Design, 14(6), 2014, 3026-3034
Spectroscopic examinations of Lu3Al5O12: Pr single crystals.
Guzik Adam*1, Talik Ewa1, Pajączkowska Anna2, Szubka Magdalena1, Kusz Joachim1, Balin Katarzyna3, Urbanowicz Piotr1
1Department of Physics of Crystals, Institute of Physics, University of Silesia, Uniwersytecka 4, Katowice (Poland) 2Institute of Electronic Materials technology,Wólczyńska 133, Warsaw, (Poland)) 3Department of Solid State Physics, Institute of Physics, University of Silesia, 75 Pułku Piechoty, Chorzów (Poland) *email: [email protected]
Luminescent materials are widely applied as converter screens in fluorescent lamps, LEDs, emissive displays, x-ray and high energy particle detectors, and solid state LASERs. In most of the application areas, the luminescent compositions are applied as polycrystalline powders, however, some devices require single crystalline materials: e.g. solid state LASERs or positron emission tomographs. Scintillators based on 5d-4f luminescence of Pr3+ are considered as good candidates for detection of high-energy photons and particles. As compared to oxide scintillators based on 5d-4f luminescence of Ce3+ , the 5d-4f emission of Pr3+ is faster and lies in a shorter wavelength range. Among the garnet-type compounds Lu3Al5O12:Pr (LuAG:Pr) with its fast decay of 20 ns, light yield 18000 ph/MeV which is more than twice higher than that of well-known and wide used scintilator Bi4Ge3O12, relatively high density (6.7 g/cm 3) and Zeff (62.9) [1] is the most attractive. Single crystal materials of Lu3Al5O12:Pr and (Lu0.75Y0.25)3Al5O12:Pr were grown by the Czochralski method under nitrogen or argon atmosphere. Obtained crystals were analyzed by the Laue diffractometry confirming single crystal form, single ion mass spectroscopy – giving chemical composition as a function of crystal depth, magnetic measurements – information of the Pr3+ ion concentration in sample, XPS electronic structure. The dielectric properties investigations revealed ε' and ε'' as a function of temperature (80 - 400 K) and frequency (0.5 kHz – 5 MHz).
Figure 1. Distribution map of the Ca surface contaminator obtained by the SIMS method. Triangle etch pits are visible. At right – dislocations with migrated contaminator into core of crystals are visible( the depth is about 100 μm)
References: [1] Ogino H., Yoshikawa A., Nikl M., Kamada K., Fukuda T., “Scintillation characteristics of Pr-doped Lu3Al5O12 single crystals,” J. Crystal Growth 292, 239-242 (2006)
Crystal Growth from High-Pressure Melt and Chemical Vapor Transport of (Si,Ge)-monopnictides, a new family of 2D-semiconductors
Céline Barreteau1, Baptiste Michon, Enrico Giannini*1
1Department of Quantum Matter Physics, University of Geneva quai E.-Ansermet 24,CH-1211 Geneva 4 (Switzerland) *email: [email protected]
Layered semiconducting materials have recently grabbed the spotlight, particularly in the case of van der Waals solids that can be exfoliated into atomically thin sheets. Tunable electronic properties as well as new phenomena related to the electron confinement in one direction make these materials highly appealing for novel electronic devices. A tremendous effort is being made on binary transition metal dichalcogenides [1], but other families of compounds have been discovered and deserve increasing consideration [2]. Binary monopnictides of Si and Ge (SiP, GeP, SiAs, GeAs, …) are a promising, but longtime disregarded family of such materials, thanks to their structure made of strongly covalent slabs, weakly bonded to each other by van der Waals forces, and their semiconducting nature exhibiting band gap values in the range 0.6 – 1.3 eV. Processing and crystal growth of these compounds is challenging [3] and in some cases has been elusive so far. The high volatility of the pnictogens (particularly P) at rather low temperatures, and the high temperature needed for making Si and Ge reactive, require dedicated unconventional growth processes for the bulk crystallization of these materials. We report the successful crystal growth of various members of this family by means of either crystallization from the melt at high pressure in a cubic anvil hot press, or chemical vapor transport in sealed quartz reactors using I2 as a transport agent, or even a particular combination of both techniques. As a matter of fact, the direct vapor transport of phosphorous does not lead to the inverse sublimation and growth of the wanted compound, nevertheless I2 proved to be successful in transporting binary phosphide molecules from a precursor preformed at high pressure (in the GPa- range). The as grown crystals easily cleave into very thin micaceous sheets and exhibit the expected semiconducting behavior. The conditions for crystal growth are discussed with respect to the thermodynamic phase equilibria suggested by the assessed phase diagrams. The optimization of the growth conditions lead to the growth of mm-size layered crystals that can be mechanically exfoliated and implemented into novel nano-electronic devices.
References: [1] Chhowalla M., Shin H. S., Eda G., Li L.-J., Loh K. P., Zhang H., Nature Chemistry, 5 (2013) 263 [2] Miro´ P., Audiffred M., Heine T., Chem. Soc. Rev., 43 (2014) 6537 [3] Lee K., Synnestvedt S., Bellard M., Kovnir K., Journal of Solid State Chemistry, 224 (2015) 62
Superconductivity in single crystals of alkali metal intercalated iron chalcogenides
A. Krzton-Maziopa,1 E. Pomjakushina,2 K. Conder*2
1Chair of Inorganic Chemistry and Solid State Technology, Warsaw University of Technology, Poland
2Laboratory for Developments and Methods, Paul Scherrer Institute, Villigen, Switzerland *email:[email protected]
Interplay between superconductivity, magnetism and crystal structure in iron-based superconductors has recently attracted a great interest. Alkali metal intercalated iron chalcogenide superconductors exhibit unique behaviors which are not observed in other iron-based superconducting materials such as antiferromagnetic ordering above room temperature and iron vacancies ordering. In this work synthesis, crystal growth, structural and superconducting properties of the family of alkali metal (K, Rb, Cs) intercalated iron chalcogenides FeSe with Tc around 30K are reported. Single crystals have been grown by the Bridgman method. X-ray and neutron diffraction, micro x-ray fluorescence, magnetization and transport measurements have been applied to study the crystals. It was found that in the crystals at least two phases are coexisting - one majority magnetic phase and a diamagnetic minority phase, most probably, responsible for superconductivity. The phase separation was stated in our samples by means of the muon-spin rotation (SR), x-ray and neutron diffraction and high resolution electron backscatter diffraction.
Crystal growth of rare earth containing clathrates and mechanism of rare earth incorporation into the clathrate cages
Andrey Prokofiev1*, Robert Svagera1, Monika Waas1, Johannes Bernardi2, and Silke Paschen1
1 Institute of Solid State Physics, Vienna University of Technology, Wiedner Hauptstr. 8-10, 1040
Vienna (Austria)
2 USTEM, Wiedner Hauptstr. 8-10, 1040 Vienna (Austria)
*email: [email protected]
Type-I clathrates possess extremely low thermal conductivities, a property that makes them promising materials for thermoelectric applications. They are guest-host systems in which a large electropositive atom like Ba or alkali metals fills oversized polyhedral cavities in a covalently bound Si, Ge, or Sn framework. It is the interaction of the vibration mode of the guest atom (rattling) with the delocalized vibrations of the framework that results in the anomalously low thermal conductivity. The incorporation of cerium (Ce) into one such clathrate, the type-I clathrate Ba8Au6Si40, has recently been shown to lead to a drastic enhancement of the thermopower, another property determining the thermoelectric efficiency [1]. This incorporation appeared to be feasible only via a crystal growth process implying the crystallization of the clathrate phase from an off- stoichiometric melt with an excess of Ce and Au. The developed floating zone technique was realized in a mirror furnace. The technique was now applied to clathrates containing other rare earth elements (RE). We discuss the mechanism of RE incorporation based on the trends in the clathrate phase composition along the RE element range. Our investigation reveals that the RE content is mainly governed by two factors, the residual cage space and the electron balance in the sense of the Zintl concept [2]. The thermoelectric and magnetic properties of some RE clathrates are discussed.
References:
[1] Prokofiev A., Sidorenko A., Hradil K., Ikeda M., Svagera R., Waas M., Winkler H., Neumaier K., and Paschen S. Nature Mat. 12 1096-1101 (2013) [2] Sevov S.C.. Zintl phases. In Intermetallic Compounds, Principles and Practice: Progress; Westbrook, J. H., Freisher, R. L., Eds.; John Wiley & Sons. Ltd.: Chichester, England, 2002; 113- 132.
Flux growth at 1230°C of cubic Tb2O3 single crystals and characterization of their optical and magnetic properties
Matias Velázquez*1, Philippe Veber1, Grégory Gadret2, Olivier Plantevin3, Daniel Rytz4, Mark Peltz4, Rodolphe Decourt1
1CNRS, Université de Bordeaux, ICMCB, UPR 9048, 87 avenue du Dr. A. Schweitzer, 33608 Pessac cedex (France) 2LICB, UMR 6303 CNRS-Université de Bourgogne, Faculté des Sciences Mirande, 9 avenue Alain Savary, BP 47870, 21078 Dijon cedex (France) 3CSNSM, UMR 8609 CNRS-Université d’Orsay, Bât. 108, 91405 Orsay Campus (France) 4FEE-GmbH, Struthstrasse 2, 55743 Idar-Oberstein (Germany) *email: [email protected]
In recent years, we have unveiled a new flux method for growing single crystals of cubic rare earth sesquioxides, pure or doped, essentially for optical applications (lasers, scintillators, Faraday rotators) [1,2]. The obvious challenge to their growth in bulk single crystalline shape imposed by their high melting point is rendered more difficult by series of structural phase transitions occurring upon cooling from the melting point. For instance, Eu2O3 exhibits no less than four phase transitions and Gd2O3 three of them between room and melting temperatures [3]. The case of Tb2O3, which exhibits a melting point of 2410°C, turns out to be complicated by its mixed valence character which results in an easy oxidation at intermediate and high temperatures. These various Tb3+/Tb4+ cationic equilibria lead to different magnetic phase transitions, as measured in TbO2, TbO1.823, Tb11O20, Tb4O7 and Tb7O12. To the best of our knowledge, the crystal growth of cubic pure Tb2O3 crystals has never been achieved nor reported. In this work, we present the first crystal growth of cubic Tb2O3 single crystals by a hydrogen free and controlled atmosphere flux method which uses a heavy metal free solvent working between 1235°C and 1160°C, that is, at less than half the melting temperature of this sesquioxide. Cubic millimeter-sized crystals extracted from as-grown boules are phase (powder XRD) and chemically (GDMS) pure and exhibit a Verdet constant which is at least three times higher than that of a commercial Tb3Ga5O12 (TGG) crystal, in the visible and near-infrared spectral ranges. The 1.36 mm thick crystals display a transmission coefficient higher than 77% over the 525 nm–1.38 μm spectral range, which corresponds to an absorption coefficient of 0.17 cm-1 at 1064 nm. The absorption spectrum, magnetic susceptibility and specific heat measurements on the single crystals confirm the absence of any detectable Tb4+ cations and other impurities. Thus, our growth process was found to remarkably stabilize the Tb3+ oxidation state in Tb2O3 without resorting to any post-growth thermal treatment and the first Verdet constant measurements in the NIR spectral range suggest that these crystals have great potential as Faraday rotators as compared to well-known TGG crystal. Emission spectra recorded at room temperature and 10 K, coupled with crystal field analysis will provide beginnings of an explanation for this remarkable property.
References: [1] Ph. Veber, M. Velázquez, V. Jubera, S. Pechev, O. Viraphong, CrystEngComm. 13 (16) (2011) 5220. [2] Ph. Veber, M. Velázquez, G. Gadret, D. Rytz, M. Peltz, R. Decourt, CrystEngComm, 17 (3) (2015) 492. [3] M. Foex, J.-P. Traverse, Rev. Int. Hautes Temp. Refract., 3 (1966) 429.
POSTER
S11-P02 Growth of p-Type ZnOS Films by Pulsed Laser Deposition
Kenkichiro Kobayashi*1, Tohru Ohtsuki1, Yasumasa Tomita1, Yosiumi Kohno1, Yasuhisa Maeda1, and Shigenori Matsushima2 1Shizuoka University, 3-5-1, Johoku, Hamamatsu (Japan) 2Kitakyushu National College of Technology, 5-20-2, Shii, Kitakyushu (Japan) *email: [email protected]
White light-emitting diodes (LED) have been developed by using Ga1-xInxN-based blue LEDs and yellow phosphors. From viewpoints of resources and cost, the substitutes for Ga and In atoms are required. ZnO is one of promising substitutes because of its abundant raw materials and non- toxicity. In recent, the strong bowing effect of the valence band was found in ZnO1-xSx (ZnOS) films. In the range of 0 Intensity / arb. unit arb. / Intensity 0 Transmittance% / 25 30 35 40 45 200 400 600 800 1000 Wavelength / nm 2 / degree Figure 1. X-ray diffraction patterns of ZnOS films(left) and their transmission spectra (right)as a function of S-sublimation temperatures in PLD processes. S11-P04 On the crystal growth, characterization and magnetic properties of two new phases discovered in the PbO-Fe2O3-P2O5 system Matias Velázquez*,1, Hassan El Hafid1, Olivier Pérez2, Abdelaziz El Jazouli3, Alain Pautrat2, Rodolphe Decourt1, Philippe Veber1, Oudomsack Viraphong1 and Claude Delmas1 1CNRS, Université de Bordeaux, ICMCB, 87 avenue du Dr. A. Schweitzer, 33608 Pessac cedex (France) 2Laboratoire de Cristallographie et Sciences des Matériaux, UMR 6508 CNRS/Université de Caen, 6 Boulevard du Maréchal Juin, 14050 Caen cedex 04 (France) 3Laboratoire de Chimie des Matériaux Solides, URAC 17, Université Hassan II Mohammedia, Faculté des Sciences Ben M’Sik, Casablanca (Morroco) E-mail: [email protected] A new oxyphosphate compound PbFe3O(PO4)3 has been discovered and grown in single crystalline shape by a combination of Bridgman and self-flux methods. Its crystal structure was characterized by single crystal X-ray diffraction (XRD) between 293 and 973 K (monoclinic symmetry P 21/m, a=7.5826 Å, b=6.3759 Å, c=10.4245 Å and =99.956°, Z=2, at room temperature) [1]. DC magnetic susceptibility and specific heat measurements performed on single crystals unveiled an unusual sequence of second order ferromagnetic-like phase transitions at Tc1=31.8 K, Tc2=23.4 K and Tc3~10 K. AC magnetic susceptibility suggests a glassy-like dynamics between ~20 K and Tc3. The magnetic behaviour of this new compound may open a possibility to test spin-glass/FM or AFM coexistence theories with real systems of localized S=5/2 spins in a virtually non disordered phase [1,3]. The closeness of the three ferromagnetic-like magnetic phase transitions observed for the first time on single crystalline samples, may offer an opportunity to investigate the vicinity of multicritical points in « T-J0 » phase diagrams in fixed 0H field. The exact nature of the successive magnetic phases at low temperature has to be firmly established by elastic and inelastic neutron diffusion. The observed critical mean-field behaviour must also be confirmed (universality class, possible crossovers) on well oriented single crystals with an optimized demagnetizing field factor [1,2]. Further exploration of the PbO-Fe2O3-P2O5 system led to the discovery of a new langbeinite phase, Pb1,5Fe2(PO4)3, the crystal structure of which was solved by room temperature single crystal XRD (P213, Z=4, a=9,7831(2) Å). This phase does not undergo any structural phase transition down to 6 K nor any kind of long range ordering down to 2 K, as found by specific heat and magnetic susceptibility measurements. Our investigations show that directional solidification of high-temperature solutions can be an interesting tool for exploratory crystal growth research. References [1] Hassan El Hafid, Matias Velázquez, Olivier Pérez, Abdelaziz El Jazouli, Alain Pautrat, Rodolphe Decourt, Philippe Veber, Oudomsack Viraphong and Claude Delmas, Eur. J. Inorg. Chem, 36, 5486 (2011). [2] Hassan El Hafid, Matias Velázquez, Olivier Pérez, Abdelaziz El Jazouli, Alain Pautrat, Rodolphe Decourt, Emmanuel Véron, Oudomsack Viraphong and Claude Delmas, J. Sol. St. Chem., 202 (2013) 85-92. [3] Hassan El Hafid, Matias Velázquez, Abdelaziz El Jazouli, Alain Wattiaux, Dany Carlier, Rodolphe Decourt, Michel Couzi, Philippe Goldner and Claude Delmas, Solid State Sciences, 36 (2014) 52-61. S11-P05 Synthesis and structure of perovskite organic-inorganic hybrid of [NH3(CH2)4NH3CoCl4] 1,4 butane diammonium tetrachlorocobaltate Seham Kamal. Abdel-Aal Teaching assistant, Physics Department, Faculty of Science, Cairo University, Egypt. Correspondence e-mail: [email protected] A new organic-inorganic hybrid [NH3(CH2)4NH3]CoCl4, 1,4 butane diammonium tetra-chlorocobaltate has been synthesized and characterized by single crystal X-ray diffraction, The hybrid crystallize in a triclinic system, space group P¯1, with the unit cell parameters a=7.2869 (2) Å, b = 8.1506 (2)Å, c = 10.4127 (3)Å, α = 77.2950 (12)°, β = 80.0588 (11)°, γ = 82.8373 (12)° and Z=2. The final R factor is 0.064. The structure +2 II consists of organic dications [NH3(CH2)4NH3] in a zigzag structure and inorganic dianions Co ion -2 coordinated by four Cl atoms in a isolated tetrahedral structure [CoCl4] . The organic and inorganic layers connected with each other through N-H….Cl hydrogen bonds. S11-P07 Macro- and microcrystallization of rare-earth aluminum borates in multicomponent systems RAl3(BO3)4 - K2Mo3O10 - B2O3 - R2O3 (R = Y, Gd, Lu) D.A. Naprasnikov 1*, V.V. Maltsev 1, N.I. Leonyuk 1, K.N. Gorbachenya 2 1Department of Crystallography and Crystal Chemistry, Geological Faculty, MSU, Moscow (Russia) 2Belarusian National Technical University, Minsk (Belarus) *email: [email protected] Crystals of rare-earth aluminum borates RAl3(BO3)4 (R=Y or lanthanide) belong to the structural type of carbonate mineral huntite CaMg3(CO3)4, and they are the subjects of extensive studies due to their promising nonlinear optical and laser properties [1]. Therefore, investigations of micro- and nanocrystallization in viscous glass-forming borates melts is also one of the priorities on the way for searching relatively inexpensive optical glass-ceramic composites as alternative components of compact laser systems [2,3]. In this paper, LuAl3(BO3)4 (LuAB) crystals up to 4 mm were grown from high-temperature o solutions using K2Mo3O10 based fluxes in the temperature range of 1125-900 C. The most high- quality samples were obtained in the case of complex flux containing 30-40 mol.% K2Mo3O10 - 50- 40 mol.% B2O3 - 20 mol.% Lu2O3. X-ray diffraction patterns of the crystals grown are similar to those for other borate of huntite family available in the ICSD database. Spectroscopic properties of LuAB crystals doped with active ions are comparable with the same characteristics of GdAl3(BO3)4 (GdAB) crystals as it has been demonstrated earlier [3]. Glass-ceramic materials based on YAl3(BO3)4 (YAB) and GdAB were synthesized in a wide temperature range. Upon quenching melts of YAB and GdAB stoichiometries, opaque glass ceramic (glaze) is formed, and it becomes transparent with 100% excess of boric anhydride and prolonged exposure at elevated temperature (1250 and 1350oС for GdAB and YAB, respectively). The samples obtained are characterized by two types of X-ray diffraction patterns: (1) typical for amorphous material and (2) with well-defined reflections, indicating the presence of crystalline phase in a glassy matrix. As a rule, they coincide with X-ray spectra of GdAB and YAB crystals. The electron microscope images of YAB-containing glazes demonstrate cavities, most likely, associated with the removal of volatile components during crystallization process. According to microprobe analysis, there are areas of different composition in glass matrix that could also indicate the formation of nano-sized crystallites. In the transparent GdAB-composites needle microcrystals detected, while there are two types of micro-crystals in the glaze: elongated individes (up to several microns) with a ratio of length to width about 10/1 and idiomorphic prismatic ones. Using the X-ray microtomography method, it was found that crystalline phase content in selected volume (1 mm3) of glass matrix is up to 32.5%, while the content of cavities corresponds to 0.35%. The absorption spectra measured for (Er,Yb):YAB-containing glass-ceramic are comparable with the spectra of Er and Yb co-doped functional phosphate glasses. References: [1] Ballman A.A., Amer. Mineral., 47 (1962) 1380 [2] G. Karlsson et al., Appl. Phys., B 75 (2002) 41 [3] Gorbachenya K.N. et al., Optics Letters, 38(14) (2013) 2446 S11-P09 Structural Characterization of Cobalt Oxide Core-Shell Nanostructure Lukić-Petrović Svetlana*1, Tadić Marin 2, Petrović Dragoslav1, Štrbac Goran1, Ivetić Tamara1 1Department of Physics, Faculty of Sciences, University of Novi Sad, Trg Dositeja Obradovića 4, Novi Sad (Serbia) 2Condensed Matter Physics Laboratory, Vinča Institute, University of Belgrade, P.O. Box 522, Belgrade (Serbia) *email: [email protected] Spinel-type cobalt oxide (Co3O4) is a p-type semiconductor with an energy gap of 1.41.8 eV and antiferromagnetic properties [1], but when in the form of nanoparticles, shows ferromagnetic- like properties at room temperature [2]. Co3O4 nanoparticles in silica matrix were synthesized using utilizing sol-gel combustion (SGC) method. The crystalline structure and morphology were investigated in detail using X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). Characteristic Raman-active modes for normal spinel cubic Co3O4 were observed. The individual Raman band position, relative intensity and FWHM parameter were determined by Lorentz line shape peak fitting (Figure 1). The average crystallite size was calculated to be approximately 9 nm from the obtained XRD data and using the Scherrer relation, while SEM images that were taken at astonishing magnifications up to 300,000 also pointed to well crystallized core-shell Co3O4/SiO2 nanostructure. Figure 1. As-synthesized Co3O4/SiO2 nanostructure: (a) XRD pattern and (b) fitted to Lorentz line shape Raman spectrum (black dots-experimental points, straight red line-fitted), and its SEM images. Acknowledgments: Bilateral cooperation between the Republic of Serbia and the Republic of Slovenia, APV Provincial Secretariat for Science and Technological Development and Ministry of Education, Science and Technological Development of the Republic of Serbia. References: [1] Tang C-W., Wang C-B., Chien S-H., Thermochimica Acta, 473 (2008) 68-73. [2] Tadic M., Panjan M., Markovic D., Stojanovic B., Jovanovic Dj., Milosevic I., Spasojevic V., Journal of Alloys and Compounds, 586 (2014) S322-S325. S11-P11 Low Temperature Growth of Cu2ZnSnS4 Thin Films by Metal Xanthate Precursors Akiko Mochihara1, 2, Kenji Yoshino1, 2, *, Naoya, Komaki1, Minobu Kawano3, Yuhei Ogomi2, 3, Qing Shen2, 4, Taro Toyoda2, 4, Shuzi Hayase2, 3 1Department of Electrical and Electronic Engineering, University of Miyazaki, 1-1 Gakuen Kibanadai-nishi, Miyazaki 889-2192, Japan 2CREST, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan. 3Department of Engineering Science, Faculty of Informatics and Engineering, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan. 4Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, 2-4 Hibikino, Wakamatsu, Kitakyushu 808-0196, Japan *email: [email protected] In recent years, the Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) compound semiconductors are potential alternative materials to CuInGaSe2 (CIGS) for thin film photovoltaic absorber layers. This is because all of the elements in CZTS and CZTSe are abundant in the earth, and the bandgap energy is controlled by the ratio of S and Se. Therefore, environmental concerns are eliminated with these materials, paving the way for gigawatt scale mass production of solar cells. Despite their brief history in solar cell technology, CZTS, CZTSe, and Cu2ZnSn(S,Se)4 (CZTSSe) solar cell devices are rapidly advancing in the solar cell markets. For example, CZTSSe solar cells fabricated at IBM have achieved an efficiency of 11.1% using a hydrazine solution process [1]. Shin et al. have reported CZTS thin-film solar cell with an efficiency of 8.4% using a vacuum based thermal evaporation process [2]. Repins et al. have reported CZTSe solar cells with an efficiency of 9.2% using co-evaporation process [3]. In this work, CZTS thin film on glass substrate is grown by dipping-coat from Cu-, Zn- and Sn-xanthate solution as precursor materials. The samples are annealed under nitrogen atmosphere. X-ray diffraction (XRD), electron probe microanalysis (EPMA), scanning electron microanalysis (SEM), thermoprobe analysis and the four-point probe method are carried out. The XRD spectra indicate that a peak of CZTS (112) starts to observe at 150 °C. This temperature is lowest in non-vacuum process of CZTS film. The all samples indicate chalcopyrite structure and polycrystalline as evidenced by the XRD spectra. A value of full width at half maximum of (112) peak increases with increasing temperature. This indicates that an grain size increases with increasing annealing temperature. The samples are non-uniform composition such as Cu-poor and Zn-rich at low temperature and become S-poor with increasing temperature. Sulfur evaporates because vapor pressure of sulfur is high. The all samples are p-type conductivity by thermo prove analysis because Cu vacancy (VCu) defects is dominant in the samples from EPMA results. The resistivity increases with the increasing annealing temperature. It is assumed that this reason is due to decreasing carrier concentration. Donor type defects such as (VS) increases with increasing the annealing temperature. References: [1] T. K. Todorov, J. Tang, S. Bag, O. Gunawan, T. Gokmen, Y. Zhu, and D. B. Mitzi, Adv. Energy Mater. 3 (2013) 34. [2] B. Shin, O. Gunawan, Y. Zhu, N. A. Bojarczuk, S. J. Chey, and S. Guha, Prog. Photovol: Res. Appl. 21 (2013) 72. [3] I. Repins, C. Beall, N. Vora, C. DeHart, D. Kuciauskas, P. Dippo, B. To, J. Mann, W. C. Hsu, A. Goodrich, and R. Noufi, Sol. Energy Mater. Sol. Cells 101 (2012) 154. S11-P12 Formation of microcrystalline SrB4O7 :Sm2+ dots in SBO glass-ceramic Głowacki Michał 1*, Martín Inocencio R. 2, Pérez-Rodríguez Carla 2, Berkowski Marek 1 1 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland) 2 Departamento de Física, Instituto de Materiales y Nanotecnología (IMN),Universidad de La Laguna, Av. Astrofísico Francisco Sánchez, s/n E-38206 La Laguna, Tenerife (Spain) *email: [email protected] Strontium tetraborate – SrB4O7 (SBO) – is a compound with high mechanical strength, high optical damage threshold and excellent non linear properties [1]. Doped with lanthanide ions SBO can be used as visible light emitting material. The oxidation state of dopant ion (thus also the emission spectra) depends on the form of the obtained material (crystal/glass) as well as on the crystal growth method [2]. This work is aimed to create SBO:Sm, where areas doped with di- and trivalent samarium ions were 2+ spatially distinct. As a result SBO glass with microcrystalline SrB4O7 : Sm dots is presented. Peculiarities of the formation of the microcrystalline dots on SBO glass and results of structural and optical investigations will be discussed. According to [3] in the glass of SBO:Sm one can observe only Sm3+ emission lines, but due to the crystallization process carried out using 3,5 W Ar laser beam focused in one spot on the surface of the SBO:Sm glass the emission peaks coming from Sm2+ ions in a crystalline environment can be detected. Therefore, presence and intensity of Sm2+ luminescence spectral lines became an indicator for microcrystalline dot formation (Figure 1.). a) b) Figure 1. a) Intensity of Sm2+ emission in SBO microcrystalline dot; b) diffraction spectra of SBO glass and crystalline sample Acknowledgements: The work was funded by the Polish National Science Center (NCN) on the basis of the decision number DEC- 2013/09/D/ST5/03878 References: [1] Yu.S. Oseledchik, A.L. Prosvirnin, V.V. Starshenko, V.V. Osadchuk, A.I. Pisarevsky, S.P. Belokrys, A.S. Korol, N.V. Svitanko, A.F. Selevich, S.A. Krikunov, J. Cryst. Growth 135 (1994) 373–376 [2] R. Stefani, A.D. Maia, E.E.S. Teotonio, M.A.F. Monteiro, M.C.F.C. Felinto, H.F. Brito, J. Solid State Chem. 179 (2006) 1086–1092 [3] P. Mikhail, J. Hulliger, M. Schnieperb, H. Billb, J. Mater. Chem. 10 (2000) 987-991 S11-P13 Form studies and thermodynamic evaluation of Fasoracetam BRAM, Harmsen TOM, Leyssens Institute of Condensed Matter and Nanosciences (IMCN), Laboratory of crystal engineering Place Louis Pasteur 1. Bte Lavoisier B1.75 Fasoracetam (NS-105) is a research chemical from the racetam family, a cognition enhancer, designed for treatment of Alzheimer’s disease1. In this study, we performed a form study of this active pharmaceutical ingredient. Two crystalline forms of fasoracetam were discovered and subjected to thermal analysis. The forms were indentified as a stiochiometric fasoracetam hydrate and fasoracetam anhydrate as confirmed through both XRD and thermal analysis. The stiochiometry observed for the hydrated fasoracetam was confirmed by TGA. The anhydrate is stable at ambient conditions after prolonged exposure and does not undergo a solid-state transition to the hydrated form. DSC curves for both compounds show a large difference in melting point (57°C hydrated and 92°C anhydrate form), of which the lower melting point for the hydrate could be attributed to a less favored crystal lattice due to the presence of water. References 1. Ogasawara T, Itoh Y, Tamura M, Mushiroi T, Ukai Y, Kise M, Kimura K. Involvement of cholinergic and GABAergic systems in the reversal of memory disruption by NS-105, a cognition enhancer. Pharmacol Biochem Behav 1999;64:41-52. S11-P15 Crystal and electronic structure and magnetic properties of Gd7Pd3-xNix intermetallics Ewa Talik*1, Adam Guzik1, Monika Oboz1,Joachim Kusz1, Paweł Zajdel1, Maciej Zubko2 1Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, Poland. 2Institute of Materials Science, University of Silesia, ul. 75 Pułku Piechoty 1a, 41-500 Chorzow, Poland. *email: [email protected] Recently, the single crystals of the Gd7-xYxPd3 series (x = 0–6) were investigated to find the influence of nonmagnetic yttrium substitution on the hybridization process, magnetic interactions and magnetic entropy changes [1]. This work presents X-ray diffraction, SEM/EDX, TEM, ac and dc - magnetic susceptibility and magnetocaloric examinations results of the Th7Fe3-type Gd7Pd3-xNix series. No structural transformation is observed upon doping with nickel and the unit cell volume decreases due to difference between radii of Pd and Ni. The magnetization phenomena are very sensitive to the applied dc magnetic field resulting in thermomagnetic hysteresis even in the weakest fields. Ni substitution into Pd positions causes the decrease of the Curie temperature. Just below the TC, the Hopkinson peak is observed due to competition between local anisotropy and spontaneuos magnetization. A dispersion of the ac-susceptibility is observed at different frequencies, which vanishes at the Curie point. In all compounds a magnetic reorientation processes is observed around 150 K. The maximum entropy is slightly higher for Gd7Pd2Ni in comparison to the parent compound due to higher disorder in the spin field. Acknowledgements This work was partially financed by the Polish National Science Centre (Narodowe Centrum Nauki) under Grant No. 2011/03/B/ST5/01035. G d Gd PdNi 4 7 2 f Gd Pd 7 3 Gd Pd Ni 7 2 P d 4 -0.3 0 0.3 0.6 d Intensity (arb.u.)Intensity G d N 5 i p 3 G d d 5 d 0 10 20 30 Binding energy (eV) Figure 1. XPS valence band, Gd4f and Gd5p of the examined compounds. The insert shows the density of states at the Fermi level. References: [1] Talik E., Oboz M., Kusz J., Winiarski A.and Hofmeister W., J. Alloys and Compounds 582 (2014) 718. S11-P16 New fluorescent hybrid materials in oxyfluoride glass matrix Olga Petrova, Ilya Taydakov, Maria Anurova, Alina Akkuzina, Roman Avetisov, Andrew Khomyakov, Igor Avetissov* D .Mendeleyev University of Chemical Technology of Russia, Miusskaya pl.9, Moscow (Russia) *email: [email protected] Hybrid materials (HM) based on metal-organic phosphors and inorganic glasses are promising materials for creating new light emitting devices [1]. Hybrid materials were synthesized by a high temperature reaction. The organic phosphors based on Eu and Al complexes which we used to produce HM’s are presented in the Table. An easy melting 80PbF2-20B2O3 glass was used as a glassy matrix. HM’s synthesized at 600C during 30 seconds at the melt stirring. The produced HM’s were yellowish glassy plates. They demonstrated photoluminescence (PL) of varying intensity in the range of emission colors from red to green when excited by 377 nm diode. PL spectra of the HM’s based on Eu-complexes had a distinguished line of Eu3+ transition (max=611 nm), but for the HM’s based on Eu(NTA)3(Bath) and Eu(NTA)3(Phen) (Fig. 1, lines 3 and 4), the intensity of the spectrum short-wave part (=400-580 nm) was more intense. We have assumed that there is an exchange reaction accompanied by partial decomposition of organic complexes. At the same time Eu3+ ions migrate into the glass matrix, and this causes the reduction of PL intensity to the values typical for inorganic glasses doped by Eu3+. Simultaneously, the ligands are bonding into complexes with Pb [2], and PL of the Pb based complex in the HM becomes more intense. The Pb-complex formation is confirmed by PL peak's positions which cannot be attributed to transitions between the levels of the individual ligands. For HM based on Alq3 (Fig. 1, line 5), PL spectrum corresponds to α-Alq3 [1], i.e the exchange reaction does not take place. Contrary to solution reactions we developed a synthesis technique for new luminescent materials by conducting a high-temperature exchange reaction between an inorganic glass matrix and organic complexes. The research was supported by the Russian Science Foundation grant № 14-13-01074. Chromaticity Abbreviati № Phosphor coordinates on CIE 4,4,5,5,6,6,7,7,8,8,9,9,9-tridecafluoro- 1-(1-methyl-1H-pyrazol-4-yl) nonane- Eu(L1) X=0.3476 1 3 1,3- dionato-(1,10-phenanthroline) (Phen) Y=0.3272 europium 4,4,5,5,6,6,6-heptafluoro-1-(1-methyl- Eu(L2) X=0.2938 2 1H-pyrazol-4-yl)hexane-1,3- dionato- 3 (1,10-phenanthroline) europium (Phen) Y=0.2630 Tris(4,4,4-trifluoro-1-(2-naphthyl) Eu(NTA) X=0.2592 3 butane-1,3-dionato-(4,7-diphenyl- 3 1,10-phenantroline) europium (Bath) Y=0.3749 Tris(4,4,4-trifluoro-1-(2-naphthyl) Eu(NTA) X=0.2054 4 butane-1,3-dionato-(1,10- 3 phenanthroline) europium (Phen) Y=0.2769 X=0.2708 5 Tris(8-hydroxyquinoline) aluminum Alq 3 Y=0.4997 Figure 1. Luminescence spectra of HM (1–5) (figures correspond to the sample numbers in Table). References: [1] Petrova O.B. et al. Eur. J. Inorg. Chem. 2015 (2015), №7, 1269–1274 [2] Marandi F. et al. Inorg. Chim. Acta. 363 (2010), 4000–4007 S11-P17 Crystal engineering of molecular salts for single-crystal to single-crystal [2+2] cycloaddition photoreactions Spinelli Floriana* 1, d'Agostino Simone1, Braga Dario1, Grepioni Fabrizia1 1Dipartimento di Chimica Ciamician,University of Bologna, Bologna (Italy) *email: [email protected] In the last decades [2+2] cycloaddition photoreactions in the solid state have attracted the attention of many researchers [1]. As a rule-of-thumb, when the molecular arrangement found in the crystal packing satisfies the Schmidt’s criterion - i.e. double bonds are parallel and at a separation of approximately 4.2 Å [2] - efficient and selective reactivity is observed in most cases. Solid-state reactivity is of great interest, as solvent-free, solid-state processes represent a “green chemistry” approach to the synthesis of new materials [3]. In this study we report on the single crystal-to-single crystal (SCSC) photoreactivity of molecular salts of cinnamic acid derivatives. Reactions for such class of compounds have been monitored by means of polarized light microscopy and single crystal X-ray diffraction. Following the structural response to UV via single crystal XRD at various irradiation intervals, it has been possible to conduct a detailed kinetic study directly in the SC medium. Figure 1. Scheme of a [2+2] photoreaction involving properly aligned olefins in the solid state. References: [1] Cohen, M.D. The photochemistry of organic solids. Angew. Chem. Int. Ed. Engl 14 (1975), 386. [2] (a) M. D. Cohen and G. M. J. Schmidt, J. Chem. Soc., (1964), 2000; (b) G. M. J. Schmidt, Pure Appl. Chem., 27 (1971), 647. [3] D. Braga, F. Grepioni, Making Crystal by Design: Methods, Techniques and Applications; Wiley-VCH, Weinheim (2007). S11-P18 Crystallization of a New Calcium Bisphosphonate through Octacalcium Phosphate Digestion Boanini Elisa*1, Gazzano Massimo2, Bigi Adriana1 1 Department of Chemistry “Giacomo Ciamician”, University of Bologna, via Selmi 2, 40126 Bologna (Italy) 2 ISOF-CNR, Bologna (Italy) *e-mail: [email protected] Bisphosphonates such as Sodium Alendronate are widely recognized as potent inhibitors of osteoclast activity and clinically used for the treatment of diseases associated with bone loss, such as osteoporosis, Paget’s disease and osteolytic tumors [1]. On the other hand, the prolonged use of these drugs was demonstrated to cause over-suppression of bone metabolism leading to osteonecrosis, especially of the jaw [2]. This drawback stimulated many studies for the development of strategies for local administration, even in combination with calcium phosphates, which mimic the structure and chemistry of bone inorganic component [3]. In particular, Alendronate was previously shown to interact with the Calcium ions of Hydroxyapatite through a bidentate chelation of deprotonated oxygen atoms [4]. Herein we investigate Octacalcium phosphate, Ca8H2(PO4)6•5H2O (OCP), as an alternative to Hydroxyapatite for the local administration of Alendronate. The results of the structural, spectroscopic, and microscopic investigation show that soaking OCP into Alendronate solutions provokes the deposition of small crystalline rod-shaped formations onto the larger crystals of calcium phosphate. The amount of Alendronate loaded onto OCP increases as a function of the Bisphosphonate concentration in solution. Indeed, we demonstrate that Alendronate in solution is able to recruit Calcium ions from OCP crystals, yielding the quantitative formation of crystalline Calcium Alendronate monohydrate, CaALH2O (figure 1). At high concentration, Alendronate craving for Calcium ion causes displacement of Ca2+ from calcium phosphate crystalline structure which results in the complete digestion of OCP [5]. Figure 1. A view of the CaAL·H2O structure. References: [1] Russell R.G.G., Bone, 49 (2011) 2. [2] Pazianas M., Abrahamsen B., Bone, 49 (2011) 103. [3] Boanini E., Torricelli P., Gazzano M., Giardino R. Bigi A., Biomaterials, 29 (2008), 790. [4] Boanini E., Gazzano M., Rubini K., Bigi A., Advanced Materials, 19 (2007) 2499. [5] Boanini E., Torricelli P., Gazzano M., Fini M., Bigi A., Advanced Materials, 25 (2013) 4605. S11-P19 X-Ray diffraction and Raman spectroscopy studies of temperature induced phase transitions in Sr3-xCaxFe2TeO9 (0 ≤x≤ 1) triple perovskite Abdelhadi Elhachmi 1,*, Bouchaib Manoun 1, P. Lazor 2. 1 Laboratory of materials science, backgrounds and modeling. FP Khouribga, University Hassan 1st, Hay Ezzaitoune BP 145, Khouribga 25000, Morocco. 2 Department of Earth Sciences, Uppsala University, SE-752 36, Uppsala, Sweden. *Corresponding author email: [email protected] Keywords: Double perovskite, Sr3-xCaxFe2TeO9, crustal structure, Phase transition, X-ray diffraction. The families of materials type A3B2B’O9 (A= Ca, Sr, Ba; B = transition metal and B’ = Mo, W, Te or U) have recently attracted great attention as ferrimagnets compounds with low or height TC’s, in some cases, above RT. These compounds are double perovskites with crystallographic formula could be rewritten as A2B(B1/3B’2/3)O6. They, thus, display an intrinsic partial disordering over half of the perovskite (B1/3B’2/3) positions. We have prepared different materials with A= Ca, Sr; B= Fe and B’ = Mo, W, Te or U and by using XRD and Mossbauer spectroscopy we have shown that all the compounds are tetragonal and can be refined in the space group I4/m [1]. Raman and infrared spectroscopy provide valuable insight into order-disorder phenomena and are very sensitive to sample composition and structural variations, making it suitable for studying the effects of atomic substitutions in complex perovskites [2]. Recently Sr3Fe2TeO9 and Ba3CaNb2O9 complex perovskite have been studied by X-ray diffraction (XRD) [3] and Raman spectroscopy [4]. At room temperature, the crystal structure of Sr3Fe2TeO9 is tetragonal [3], s.g. I 4/m, with a = b = 5.5626(5) Å, c = 7.8634(7) Å. In the present work, using X-ray diffraction and Raman spectroscopy techniques, we report that Sr3-xCaxFe2TeO9 have a tetragonal symmetry with I4/m as space group at RT. Furthermore, increasing temperature for this compound, remarkable change in the temperature dependence of the Raman modes are illustrated, leading to high temperature induced phase transitions. References: [1] M. C. Viola, M. S. Ausburger, R.M. Pinnaca, J. C. Pedregosa, R. E. Carbonio and R. C. Mercader,J. Solid State Chem., (2003) 175, 252. [2] A. Dias, R. G. Sá, and R. L. Moreira,J. Raman Spectrosc. 39, 1805 (2008). [3] S.A. Ivanov, P. Nordblad, S.-G. Eriksson, R. Tellgren, H. Rundlo.42 (2007) 776–78 [4] Joa ˜o Elias Figueiredo Soares Rodrigues, Edvan Moreirab, De´bora Morais Bezerra, Adeilton Pereira Macielc, Carlos William de Araujo Paschoal, (2013) 48- 3298 –3303. S11-P20 GROWTH AND STRUCTURE OF SINGLE CRYSTAL Ba3TaFe3Si2O14 -LANGASITE FAMILY MULTIFERROICS. A.P.. Dudka and A.M. Balbashov * The Institute of crystallography RAS, Moscow, Russia, * Moscow Power Engineering Institute. e- mail : dudka @ ns.crys.ras.ru By floating zone melting method on the equipment of URN-2-ZP [1] are grown single crystals Ba3TaFe3Si2 O14 (BTFS). BTFS belongs to the family of langasite (space gr. P 321 [2], [3]), it contains magnetic ions Fe3+, shows the magnetic ordering, and is promising multiferroic [4], [5], [6] . Iron contained langasites are grown at the control pressure of oxygen above the melt within 1-30 atm. and annealing during crystal growing process at a temperature of about1000 oC and smooth temperature decreasing for 5 h. Speed growth was 7-10 mm/h at rotation of crystal 40 rpm. and feed rod-1rpm. For ensure a smooth polycrystalline feed rod melting at growing of single crystal feed rod preliminary was remelted by floating zone at speed 35 mm/hour in the air. On [7] was made precision x-ray analysis of BTFS crystal structure using repeated high resolution data sets at 295K and 95K (ICSD 429640, 429641). Quality of single crystal is confirmed by criteria of structure refinement models: at 295K - R / wR = 1.02/ 1.23% for 4552 independent reflections; at 95 K- R / wR = 1.01- 1.14% for 4501 reflections. Asymmetry of disordering of atomic positions of magnetic Fe ion in position (3f) and Ba cation in position (3e) was identified. At cooling atoms of Ba(3e) and Fe(3f) move on the double axis of symmetry in opposite directions, and Si(2d) shifts on triple axis (i.e. changing the 3 parameters from 10 possible). In BTFS pronounced helicoidal screwing of electron density along the c axis of the crystal [8], the axis of the helix runs through the atom Ta(1a). Fixed helix is a structural basis for magnetic ordering in BTFS. [1] . A.M. Balbashov, S.K. Egorov.,. J. Cryst. Growth. 1981. V. 52. P. 498. [2] . E. l. Belokoneva and . N.V. Belov, Dokl. Akad. Nauk USSR, 260 (6), 1363 (1981). [3] B.V. Mill`., Yu. V. Pisarevsky. Proc. IEEE/EIA 2000 Intern. Frequency Control Symp., Kansas City, Missouri, USA. P. 133. [4] . V.Yu. Ivanov., A.A., Mukhin, A.S Prokhorov. B.V. Mill`. Solid State Phenomena. 2009. V, 152-153. P. 299. [5] . K. Marty ., P. V. Bordet Simonet,. et al. Phys. Rev. b. 2010. V. 81. 054416. [6] . I.S. Lyubutin., P.G.Naumov, B.V. Mill`. et al. . Phys. Rev. B. 2011. V. 84.214425. [7] . A.P. Dudka., J. Appl. Cryst. 2007. V. 40. P. 602. [8] . A. P. Dudka and B. V. Mill ', Crystallogr. Rep. 59 (5), 759 (2014). S11-P22 Large GaPd2 single crystals grown by the Czochralski technique Schwerin Judith*1, Müller Dirk1, Burkhardt2 Ulrich, Simon Paul2, Grin Yuri2, Gille Peter1 1Ludwig-Maximilians-Universität München, Department of Earth and Environmental Sciences, Crystallography Section, Theresienstr.41, 80333 München (Germany) 2Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Straße 40, 01187 Dresden (Germany) *email: [email protected] The intermetallic compound GaPd2 (Co2Si structure type, space group Pnma [1]) shows excellent catalytic properties like a high selectivity and long-term stability. Because of these outstanding characteristics this binary compound can be used as a highly active heterogeneous catalyst in the semi-hydrogenation of acetylene [2]. Although single crystals are not used in technical application for catalysis, they are necessary to understand the basic catalytic processes. Many techniques in surface science require large (cm3) single crystals to study the substances´ intrinsic properties. Single crystals of GaPd2 were grown by the Czochralski technique from Ga-rich off-stoichiometric solutions. An insufficient material transport of the Ga excess next to the growth interface may lead to mother liquid inclusions in the grown crystal but the use of extremely low pulling rates (0.025 mm/h) and higher-temperature regions of liquidus balance better the materials transport to the growth interface. GaPd2 is characterized by a broad stability region with a retrograde solubility of the Ga excess component [3]. This leads to supersaturation of the Ga component during post-growth cooling and is the driving force for precipitation of the orthorhombic phase Ga3Pd5 (Ge5Rh3 structure type, space group Pbam [4]). In a GaPd2 crystal grown in [001] direction this mechanism has been observed as two-phase region of GaPd2 and Ga3Pd5 which are ordered in alternate lamellas (2-6 µm) perpendicular to the growth direction. This is the in-situ observation of the formation of the intergrowth structures predicted previously [5]. Diffraction Laue back–scattering images show a coherent ordering of the two-phase lamellas. The change of the growth direction of the GaPd2 crystals changes the orientation of the lamellas keeping the coherent intergrowth unchanged. EPMA measurements have shown different stages of decomposition of these lamellas from Pd2-xGa1-x to entirely decomposed Ga3Pd5. The total decomposition to Ga3Pd5 under certain conditions was confirmed by annealing experiments. Because of growth temperatures much higher than the peritectic one of Ga3Pd5 (~ 1030°C [3]), primary crystallization of Ga3Pd5 from the liquid solution can be excluded [6]. High-resolution TEM measurements confirm these conclusions on atomic level. Lamellas of both phases a few nm thick exist, which cannot be resolved by EPMA. The two phases have a shared interface unit cell with (001)GaPd2 (010)Ga3Pd5 with a lattice parameter misfit < 1%. Stacking faults and smooth transition between the two phases was observed in the transition area. These results suggest that the phase separation occurs due to the concentration variation during the crystal growth. References: [1] Kovnir, K., Schmidt, B., Waurisch, C., Armbrüster, M., Prots, Yu., Grin, Yu. Z. Kristallogr. NCS 223 (2008) 7-8. [2] Armbrüster, M., Kovnir, K., Behrens, M., Teschner, D., Grin, Yu., Schlögl, R., J. Am. Chem. Soc. 132 (2010) 14745-14747. [3] Okamoto, H., J. Phase Equilibr. Diffus. 29 (2008) 466-467. [4] Schubert K., Breimer, H., Gohle, R., Lukas, H.L., Meissner, H.G., Stolz, E., Naturwissenschaften 45 (1958) 360-361. [5] Grin, Yu. In: Modern Perspectives in Inorganic Crystal Chemistry. Kluver AP, (1992), p. 77. [6] Schwerin, J., Müller, D., Kiese, S., Gille, P., J. Cryst. Growth (2014) 613-616. S11-P23 Synthesis and crystal growth of NdAl3(BO3)4 with different polytypic structures E.A. Volkova*, V.V. Maltsev, N.I. Leonyuk Department of Crystallography and Crystal Chemistry, Geological Faculty, MSU, Moscow (Russia) *email: [email protected] Borates RM3(BO3)4 (R = Y or rare earth metal, M = Al, Ga, Cr, Fe, Sc) with huntite derivative crystal structures are well known multifunctional materials. Among others, NdAl3(BO3)4 (NAB) crystals with huntite-like structure (sp. gr. R32) without center of inversion can be used as self-doubling laser media. The second harmonic generation intensity in these crystals is 6 times 3+ higher than, for example, in wide spread used KH2PO4 (KDP) material. High Nd concentration 21 -3 3+ 4 4 (5.43x10 cm ) and fluorescence lifetime of the Nd ion F3/2 → I11/2 transition in NAB crystal at 19 µs allow it to be applied in miniature, high-efficiency source pumped by semiconductor lasers or LED's, using the 0.8 µm Nd3+ absorption band. CW laser action from this crystal can be also obtained in the vicinity of 1.3 µm wavelength. The emission cross section in NAB is 2.1 times 3+ higher than, for instance, in Y3Al5O12:Nd . Also, considering its extremely high thermal conductivity of about 12.7 W/m*K [1,2], this implies applications of NAB material in communication laser systems and integrated optics. For this reason, a number of publications is devoted to flux growth of NAB single crystals, taking into account its incongruent melting. On the other hand, as it follows from the literature, this crystal has polytypic structures having the following space groups, depending on the crystal growth conditions: R32, C2/c, C2 [3], P6/mmm (P6/m), C2 [4], R32, C2/c and C2 [5]. So far, however, there is no precise data on their phase transition temperatures, and it is not easy to obtain NAB single crystals of optical quality and sufficient sizes. So, the major problem which awaits clarification is precise determination of crystal growth conditions for non-centrosymmetric and centrosymmetric NAB modifications. The present work is aimed at assessment of optimal experimental conditions for the NAB crystal growth. At the first stage, sintering procedure in the Nd2O3-Al2O3-B2O3 system was investigated using XRD measurements for better understanding of NAB mechanisms formation on this way. NAB powders were obtained by solid-state reaction method. At the second stage, NAB single crystals were obtained from K2Mo3O10 based flux systems. XRD measurements were used for phase analysis of the samples sintered. The experimental powder diffraction patterns were subjected to quantitative phase analysis, in order to identify a ratio of rhombohedral and monoclinic phases over the NAB specimens. Rietveld refinement method has revealed, at least, two phases, namely R32 and C2/c in all synthesized samples. In some cases, the third modification C2 was also observed. The ratio of these phases is strongly depended on the crystallization temperature and composition of the fluxed melt. This research was supported in part by the RFBR grant # 14-05-90000-bеl_а. References: [1] D. Xue, S. Zhang, J. Phys.: Condens. Mat., 8 (1996) 1949. [2] O.V. Pilipenko, V.V. Maltsev, N.I. Leonyuk, A.B. Kozlov, A.V. Shestakov. The CIS Conf. on Crystal Growth, Ukraine, Kharkov, Oct. 1-5, 2012, Abstr. P57(A2), 155. [3] E.L. Belokoneva, N.I. Leonyuk, A.V. Pashkova, T.I. Timchenko, Sov. Phys. Crystallogr., 33 (1988) 765. [4] Y. Ji, J. Liang, Zh. Chen, S. Xie, J. Amer. Ceram. Soc., 74(2) (1991) 444. [5] G. Wang, M. He, Z. Luo, Mat. Res. Bull., 26 (1991) 1085. S11-P24 2D transition metal dichalcogenides grown by chloride driven chemical vapor transport Celine Barreteau*1, Alberto Ubaldini2, Enrico Giannini1 1Department of Quantum Matter Physics, University of Geneva, quai E. Ansermet 24, CH-1211 Geneva 4,(Switzerland) *email: [email protected] 2D transition metal dichalcogenides (TMD) exhibit interesting electronic and opto-electronic properties. Moreover, these materials crystallize in a layered structure that consists of vertically stacked layers, held together by weak Van der Waals-like interactions, which make them easily exfoliated down to atomically thin layers. Single crystals of TMDs are grown by chemical vapor transport (CVT) with, in most of the cases, I2 or Br2 as a transport agent. The choice on the transport agent affects the overall quality of the crystals and is at the origin of defects as observed in TiSe2 [1]. These defects have a direct influence on electronic structures and electronic properties of the material and the electronic devices. Going beyond the limits of this technique, thus improving the crystal quality, is possible by finding new transport agents. This is particularly needed in the presence of “heavy” transition metals (TM = Hf, Ta, Mo, W). Transition metal chloride precursors prove to be the most suitable for growing crystals of Mo and Ta [2]. Here we extend the successful use of chlorides to the growth of WX2 (from WCl6), HfX2 (HfCl4) and ZrX2 (ZrCl4). For the latter, some previous work [3] and our preliminary results showed the crucial role of the stoichiometry on the crystal structure and the morphology. This can be tuned by using the chloride as a transport agent. We will discuss the relevance of using chlorides for these compounds in order to grow large and highly pure layered single crystals of each chalcogenide. The possibility of making electronic devices for some of these crystals has been demonstrated [3]. References: [1] Hildebrand B., Didiot C., Novello A.M., Monney G., Scarfato A., Ubaldini A., Berger H., Bowler D.R., Renner, C., Aebi P., Physical Review Letters, 112 (2014) 197001. [2] Ubaldini A., Jacimovic J., Ubrig N., Giannini E., Crystal Growth and Design, 13 (2013) 4453. [3] Gleizes A., Jeannin Y., Journal of Solid State Chemistry, 1 (1970) 180. [4] Guitiierrez-Lezama I., Arora A., Ubaldini A., Barreteau C., Giannini E., Potemski M., Morpurgo A., Nano Letters, 15 (2015) 2336. S11-P26 Influence of polyols on the formation of nanocrystalline nickel ferrite inside silica matrices Marcela Stoia1, Paul Barvinschi2, Lucian Barbu – Tudoran3, Octavian Madalin Bunoiu*2 1 University Politehnica Timisoara, Research Institute for Renewable Energy, P-ta Victoriei No.2, 300006 Timisoara (Romania) 2 West University of Timisoara, Faculty of Physics, Bv. V. Parvan, No. 4, Timisoara 300223 ( Romania) 3 Babes-Bolyai University, 5-7 Clinicilor Street, 400006 Cluj-Napoca (Romania) *email: [email protected] Thermal decomposition of metal-organic precursors is one of the most succesfull methods used for the synthesis of ferrite/silica nanocomposites [1,2]. For the synthesis of nickel ferrite/silica nanocomposites, we have used a modified sol-gel method that combines the sol-gel processing with the thermal decomposition of metal-organic precursors, leading to a homogenous dispersion of ferrite nanoparticles within the silica matrix and a narrow size distribution. We used as starting materials tetra(ethoxy)silane (TEOS) as source of silica, Fe(III) and Ni(II) nitrates as source of metal cations and polyols as reducing agent (poly(vynyl alcohol), 1,4-butanediol and their mixture). The polyol interacts during gelation with TEOS leading to hybrid gels, while during the heating of the gels it reacts as reducing agent with the nitrates ions, and gets oxidized to carboxylic acids that form with the metal cations the corresponding carboxylates [2, 3]. FT-IR spectroscopy evidenced the formation of metal carboxylates inside the silica-gels and the interaction of the polyols with the Si-OH groups of the polysiloxane network. The formation of precursors as well as their thermal decomposition during heating was also investigated by TG/DTA coupled technique. X-ray diffractometry evidenced that in case of nanocomposites with one polyol, nickel ferrite forms as single crystalline phase inside the amorphous silica matrix, while in case of the mixture of polyols nickel oxide appears as secondary phase. TEM microscopy evidenced the fine nature of the obtained nickel ferrite nanoparticles, homogenously dispersed within the silica matrix. Ferrite nanoparticle size, as determined from TEM images, was in agreement with the crystallite size estimated from XRD data, leading to the conclusion that the obtained nickel ferrite nanoparticles are monocrystalline. The elemental maps evidenced that the obtained ferrite nanoparticles are homogenously dispersed inside the silica matrix. The magnetic properties of the obtained NiFe2O4/SiO2 nanocomposites depends on the nature of the organics used in synthesis, due to the modified morphology of both silica gel and nickel ferrite nanoparticles. Thermal behavior of the precursors and the final nanocomposites was studied using a 1500 MOM Budapest derivatograph. The heating was achieved in static air, in the range 25 – 500 °C, -1 with a heating rate of 10 °C min , on Pt plates using α-Al2O3 as inert material. The synthesized powders were characterized by FT-IR spectroscopy with a Shimadzu Prestige FT-IR spectrometer, in KBr pellets, in the range 400 - 4000 cm-1, in air. Phase analysis was achieved with D8 Advance - Bruker AXS diffractometer, using the MoKα radiation (λ = 0.7093 Å). SEM images have been recorded on a Quanta 3D FEG (FEI) microscope. TEM images were recorded on a Jeol-Jem 1010 Microscope. The magnetic investigations on the powders in the as-prepared state were carried out at room temperature under AC (50 Hz) applied magnetic fields of amplitudes up to 160 kA/m. References: [1] Shen X., Zhou Z., Song F., Meng X., J. Sol-Gel Sci. Technol., 53 (2010) 405. [2] Stoia M., Barvinschi P., Barbu-Tudoran L., J. Therm. Analysis Calorim., 113 (2013) 21. [3] Stefanescu M., Stoia M., Stefanescu O., Barvinschi P., J. Therm. Analysis Calorim., 99 (2010) 459. S11-P28 Optical and Structural properties of Cobalt doped Zinc Sulphide (ZnS)/α-Fe2O3 nanoparticles. Patij K. Shah. Hozefa J. Tinwala , Kirit S. Siddhapara, Dimple V. Shah 1Applied Physics Department, S. V. National Institute of Technology, Surat-395007, India email:[email protected] Optical and structural properties of Cobalt doped ZnS/α-Fe2O3 synthesized by Sol-Gel Method has been investigated. From X-Ray Diffraction (XRD) results phase of Cobalt doped ZnS/α- Fe2O3 have been observed. Energy Dispersive Spectroscopy (EDS) analysis confirms that the chemical composition is equal to the stoichoimetric composition of sample. Morphology and particle size has been observed using Scanning Electron Microscopy (SEM). Optical properties of Cobalt doped ZnS/α-Fe2O3 have been investigated using Photo-Luminescence (PL) and UV-Visible Spectroscopy. S11-P29 THERMOLUMINESCENT PROPERTIES OF POLYCRYSTALLINE CARBON DOPED LANTHANUM ALUMINATE (LAALO3:C) GROWN BY DIFFERENT SOLID STATE REACTIONS Alves Neriene1, Barbosa Ferraz Wilmar2, Oliveira de Faria Luiz*3 1Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, Belo Horizonte (Brazil) 2Centro de Desenvolvimento da Tecnologia Nuclear, Av. Antônio Carlos 6627, Belo Horizonte (Brazil) 3Centro de Desenvolvimento da Tecnologia Nuclear and Universidade Feral de Minas Gerais, Av. Antônio Carlos 6627, Belo Horizonte (Brazil) *email: [email protected] Among several potential application, Lanthanum aluminate (LaAlO3) polycrystals have attracted much attention for use in gas sensors and as catalyst for oxidative coupling of methane and hydrogenation and hydrogenolysis of hydrocarbons. Due to their excellent chemical and thermal stability they have been widely used as a substrate of high-temperature superconductor [1]. 3+ 3+ Recently, LaAlO3 single crystals, co-doped with Ce and Dy rare earth trivalent ions and grown under hydrothermal conditions, have been reported to show high thermoluminescent response (TL) when exposed to low levels of ultraviolet radiation (UVR). However, undoped LaAlO3 synthesized by solid state reaction method from the 1:1 mixture of aluminum and lanthanum oxide under reducing atmosphere revealed to have still higher thermoluminescent sensitivity to UV photon fields [2]. On the other hand, it is well known that the dopping of alfa-Al2O3 single crystals with carbon atoms has produced one of the best TL crystals commercially available [3]. Thus, we conducted three different syntheses of LaAlO3 by this solid state reaction method, doping the mixture with carbon, aiming the improvement of its TL response. The lanthanum aluminate polycrystals were synthesized from the 1:1 mixture of aluminum and lanthanum oxide, adding 0.1% carbon and annealed at 1700 ° C for two hours in hydrogen atmosphere. The X-ray diffraction analysis revealed the nucleation of rhombohedral LaAlO3 crystallographic phase, however a small percentage (15%) of Al2O3 has been also identified in all compositions. One of them presented also peaks assigned for lanthanum hydroxide, about seventeen percent (17%), which are better presented in the diffractograms in Figure 1(a). The UV irradiations were carried out using a commercial 8W UV lamp. TL output measurements were performed at a Harshaw 4500 TL reader. TL curves in Figure 1(b) shows that all compositions investigated have high TL sensitivity to UVR with also different intensities between themselves. In this work we discuss the TL output, its linear fitting with UV exposure and the annealing features for samples obtained using three different combinations of Al2O3, La2O3 and carbon atoms during the syntheses process. La O :C+Al O 2 3 2 3 La O :C+Al O 2 3 2 3 (a) Al O :C+La O 2 3 2 3 Al O :C+La O 2 3 2 3 La O +Al O + C La O +Al O + C 2 3 2 3 2 3 2 3 15 (b) 10 TL Intensity (a.u) Intensity (a.u) Intensity 5 0 50 100 150 200 250 300 10 20 30 40 50 60 70 80 2 Temperature (°C) Figure 1.(a) XRD patterns for the LaAlO3:C grown by different synthesis. ( ● ) assigned to rhombohedral phase Lanthanum aluminate (LaAlO3), (■) assigned for lanthanum hydroxide (La(OH)3) and (┼) for Aluminum oxide (Al2O3). The others peaks with less intensity are assigned for LaAl11O18, a secondary phase of Lanthanum aluminate and (b) TL curves. References: [1] Kaur, J. et al. p. 1-35, 2013/03/23 2013. ISSN 0922-6168. available in: http://dx.doi.org/10.1007/s11164-013-1126-z . [2] Alves, N. et al. Radiation Measurements, v. 46, n. 71, p. 90-94, 2011. ISSN 1350-4487. available in: http://dx.doi.org/10.1016/j.radmeas.2014.02.008. [3] McKeever, S. W. S. et al. Radiation Protection Dosimetry, v. 84, n. 1-4, p. 163-168, 1999. available in: http://www.scopus.com/inward/record.url?eid=2-s2.0- 0032766479&partnerID=40&md5=95317c6ce5f8b7293f3fdfae09ea6a80 >. S11-P31 Growth and stability of pinacol hydrates Szymon Sobczak*, Andrzej Katrusiak 1 Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznań, Poland *email: [email protected] The formation of hydrates of organic and inorganic compounds is widely studied due to the importance of such materials for their applications in pharmaceutical industry [1]. Hydration can significantly change the stability and properties of chemicals, for example the solubility and bio-accessibility of active pharmaceutical ingredients (API’s) [2]. It is known that the hydration can be changed by temperature and concentration of components, however little is known about the effects of pressure. It was shown that high-pressure recrystallization can efficiently change the preference both for precipitation of hydrates and anhydrates. For example, two hydrates of thiourea can be obtained at high pressure; monohydrate (NH2)2CS·H2O above 0.60 GPa and 3(NH2)2CS·2H2O at 0.70 GPa [3]. It was also shown that above 1.20 GPa anhydrous thiourea becomes stable again. Presently we report the effect of pressure for the recrystallization of a well-known organic substrate pinacol. This 2,3-dimethyl-2,3-butandiol has been thoroughly studied as a function of temperature. Several crystalline forms of pinacolone has been characterized by X-rays diffraction [4]: the anhydrous (monoclinic, C2/c), hemihydrate (hexagonal P6522), monohydrate (monoclinic P2/n) and a hexahydrate (tetragonal P42/mnm). We have performed in situ high-pressure crystallizations of pinacol in a diamond-anvil cell (DAC) [5]. Figure 1. In situ single crystal growth of pinacolone (a) anhydrous and (b) hexahydrate References: [1] Blagden N., de Matas M., Gavan P. T., York P., Adv. Drug Deliv. Rev., (2007), 59, 617–630. [2] Khankari R. K. and Grant D. J. W., Thermochim. Acta, (1995), 248, , 61–79. [3] Tomkowiak H., Olejniczak A., and Katrusiak A., Cryst. Growth Des., (2013), 13, 121–125. [4] Hao X., Parkin S., and Brock C. P., Acta Crystallogr. Sect. B Struct. Sci., (2005), 61, 689–699. [5] Merrill L., Bassett W. A., Rev. Sci. Instrum. 45, (1974), 290−294. S11-P33 High pressure High temperature (HP / HT) growth of multifunctional perovskites. How chemical substitutions can be used to switch from a magnetoresistive to a dielectric (polar) magnet D. Delmonte*1, F. Mezzadri2, E. Gilioli1, G. Calestani2, M. Solzi3, R. Cabassi1, F. Bolzoni1 1IMEM-CNR, Parco Area delle Scienze 37/A, 43124 Parma (Italy) 2Dipartimento di Chimica, GIAP Università di Parma, Parco Area delle Scienze 17/A 43124 Parma (Italy) 3Dipartimento di Fisica, Università di Parma, Parco Area delle Scienze 7/A, 43124 Parma (Italy) *email: [email protected] The study of multifunctional materials is today one of the most relevant branches of the wide field of Materials Science. Unfortunately such phases are often characterized by complex structural constraints which usually act as a limiting agent. In particular for what concerns the family of multiferroics, the coexistence of two or more primary ferroic orders (ferromagnetism, ferroelectricity and ferroelasticity) requires to respect strict spatial and time inversion symmetry rules and to produce materials with precise electrical properties (a multiferroic is always an insulator…). It is not casual that such compounds prevalently crystallize on the basis of the perovskite structure: due to its large tolerance to structural distortions and chemical substitutions, perovskites allow to explore wide ranges of physical phenomena. Specifically, lead-based perovskites, thanks to the very high-T ferromagnetic/ferrimagnetic character they display often above RT (a very rare phenomenon in known multiferroics), result to be very promising. However, they are bad candidate for multiferroism since semi-metallic character, magnetoresistivity and in some cases spin-polarized electrons-mediated transport (interesting aspects for spintronic applications) is often observed; in few words they are far away to be good insulators. In this work we try to explain how we operate to transform a semimetal into a dielectric (possibly polar) material limiting the weakening of its magnetic response in order to obtain a multiferroic phase. The strategy goes through a chemical operation on the A site of the perovksite; Pb ion is partially substituted with an alkali ion (principally K+). The stabilization of such a different ion in this site can be uniquely provided by means of an enhancement of the isostatic pressure intensity applied during HP/HT synthesis in our Multianvil press apparatus. This ECCG5 Congress has been endorsed by the The ECCG5 would like to thank all exhibitors and sponsors who have generously contributed to this year’s conference