DOCSLIB.ORG

Atomistic Materials Modeling of Complex Systems: Carbynes, Carbon Nanotube Devices and Bulk Metallic Glasses

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Atomistic Materials Modeling of Complex Systems: Carbynes, Carbon Nanotube Devices and Bulk Metallic Glasses ATOMISTIC MATERIALS MODELING OF COMPLEX SYSTEMS: CARBYNES, CARBON NANOTUBE DEVICES AND BULK METALLIC GLASSES DISSERTATION Presented in Partial Ful¯llment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Weiqi Luo, M.S., B.S. ***** The Ohio State University 2008 Dissertation Committee: Approved by Professor Wolfgang Windl, Adviser Professor Katharine M. Flores Adviser Professor John E. Morral Graduate Program in Professor William F. Saam Materials Science and Engineering °c Copyright by Weiqi Luo 2008 ABSTRACT The key to understanding and predicting the behavior of materials is the knowledge of their structures. Many properties of materials samples are not solely determined by their average chemical compositions which one may easily control. Instead, they are profoundly influenced by structural features of different characteristic length scales. Starting in the last century, metallurgical engineering has mostly been microstructure engineering. With the further evolution of materials science, structural features of smaller length scales down to the atomic structure, have become of interest for the purpose of properties engineering and functionalizing materials and are, therefore, subjected to study. As computer modeling is becoming more powerful due to the dramatic increase of computational resources and software over the recent decades, there is an increasing demand for atomistic simulations with the goal of better understanding materials behavior on the atomic scale. Density functional theory (DFT) is a quantum mechanics based approach to calculate electron distribution, total energy and interatomic forces with high accuracy. From these, atomic structures and thermal effects can be predicted. However, DFT is mostly applied to relatively simple systems because it is computationally very demanding. In this thesis, the current limits of DFT applications are explored by studying relatively complex systems, namely, carbynes, carbon nanotube ii (CNT) devices and bulk metallic glasses (BMGs). Special care is taken to overcome the limitations set by small system sizes and time scales that often prohibit DFT from being applied to realistic systems under realistic external conditions. In the first study, we examine the possible existence of a third solid phase of carbon with linear bonding called carbyne, which has been suggested in the literature and whose formation has been suggested to be detrimental to high-temperature carbon materials. We have suggested potential structures for solid carbynes based on literature data and our calculations and have calculated their free energies by DFT as a function of temperature (0 – 4000 K) and pressure (0-180 kbar). We propose and verify a simplified approach to calculate the phonon density of states (DOS) to allow a fast calculation of free energies. We found that all carbyne structures have higher free energies than graphite in the whole temperature and pressure range of this investigation, making pure (carbon-only) carbynes at most meta-stable. The inclusion of impurities was studied as well and may be the key for a stable carbyne phase. For CNT devices which have been suggested to eventually replace current Si technology, there is currently no equivalent for the highly used Si process modeling methods (“Technology Computer Aided Design” (TCAD)). We suggest accelerated DFT molecular dynamics (MD) simulations as a method for process modeling and apply it to study the contact formation between CNTs and metal contacts consisting of Ti, Pd, Al, and Au. The temperature accelerated dynamics (TAD) technique was adopted to overcome the time limitations of MD simulations in general, which are especially severe for the computationally demanding DFT MD simulations. We found that CNTs undergo a structural transformation when brought into contact with certain metal electrodes (here, iii Ti and Al). This resulted in a dramatic decrease in electrical conductance of the device. We also show that the transformation depends on the size of CNTs due to the size- dependent elastic energy and on the electrode materials due to the electronegativity- dependent charge transfer. In the last study, DFT was used in conjunction with classical MD simulations to predict the electron density of a Cu46Zr54 BMG structure modeled by a 1000-atom cell. Whereas DFT is capable to calculate the electron distribution in the cell, it is too slow to simulate melting and structural relaxation, which we handle by classical MD within the Embedded Atom Method. We propose a new model to analyze the open volume distribution based on the electron density and compare it with the traditional hard sphere model. Results from both models agree well, while the former allows a significantly better physical insight into the open volume distribution. As an additional plus, its results can be connected to experimental results by techniques such as Positron Annihilation Spectroscopy (PAS). iv To My Parents v ACKNOWLEDGMENTS I joined the group with limited background knowledge and encountered numerous problems during my studies. Prof. Windl carried me through all the difficulties since my first day in the group. My work wouldn’t have been possible without his endless support. More importantly, as an advisor, he always inspired me with enlightening ideas and always gave me generous help and encouragement. As a teacher, he often explained sophisticated physics to me in simple and precise language. My most sincere thanks go to him first. I am grateful to Prof. Morral and Prof. Flores, who gave me excellent advice and supported me. Moreover, they introduced me to the experimental world and made it possible for me to connect simulations to experiments. I wish to thank my fellow students, Tao Liang, Ashwini Bharathula, Naveen Gupta, Ryan Paul, Ning Zhou, Yuan Zhang, Karthik Ravichandran, Dipanjan Sen, Lanlin Zhang and Anupriya Agrawal who helped me in solving research problems and gave me a lot of laugh in my student life. They gave me very good memories during the past three years. This work was supported by the National Science Foundation and Semiconductor Research Cooperation. I am thankful for the computer time awarded by the Ohio Supercomputer Center, with which most of my simulations were performed. vi VITA 2002……………. B.S., Fudan University Shanghai, China 2005……………. M.S., Ohio State University Columbus, OH 2005-present…… Graduate Research Associate Ohio State University Columbus, OH FIELDS OF STUDY Major Field: Materials Science and Engineering vii TABLE OF CONTENTS Page Abstract............................................................................................................................... ii Dedication........................................................................................................................... v Acknowledge .....................................................................................................................vi Vita.................................................................................................................................... vii List of Tables ...................................................................................................................... x List of Figures................................................................................................................... xii Chapters: 1. Introduction..................................................................................................................... 1 1.1 Computational Materials Science ....................................................................... 1 1.2 Atomistic Modeling............................................................................................ 4 1.3 Motivation and Organization of This Thesis ...................................................... 6 2. An Introduction to the Density Functional Theory......................................................... 8 2.1 The Schrödinger Equation and Wave Functions .............................................. 10 2.2 Born-Oppenheimer Approximation.................................................................. 12 2.3 Many-Body Wave Functions ............................................................................ 13 2.4 The Variational Method.................................................................................... 13 2.5 Hartree-Fock Approximation............................................................................ 16 2.6 The Exchange and Correlation Hole................................................................. 27 2.7 The Thomas-Fermi Model ................................................................................ 30 2.8 The Hohenberg-Kohn Theorem and Kohn-Sham Approach............................ 31 2.9 Approximate Exchange-Correlation Functionals............................................. 35 2.10 Pseudo Potentials.............................................................................................. 38 3. The Structure and Stability of Carbynes....................................................................... 41 3.2 Structure and Stability of Carbynes .................................................................. 46 3.2.1 Crystal Structure of Carbyne in Previous Work ....................................... 46 viii 3.2.2 Computational Method............................................................................. 54 3.2.3 Kasatochkin-Type Carbyne.....................................................................
Load more

Recommended publications
  • Lunar and Planetary Science XXX 1753.Pdf
    Lunar and Planetary Science XXX 1753.pdf INTERSTELLAR DIAMOND. II. GROWTH AND IDENTIFICATION. Andrew W. Phelps, University of Dayton Research Institute, Materials Engineering Division (300 College Park, Dayton OH, 45469-0130, [email protected]). likely form clumps of carbon that look much like the Introduction: The first abstract in this series starting material – hydrogen rich sp3 bound clusters. suggested that many types of diamond are found in many types of meteoritic material and that the The compounds that fit the requirements above variation in polytype abundance appears to reflect the include the cycloalkanes such as adamantane [21-30] nature of the host. How the diamonds got there and (C10H16) and bicyclooctane (C6H8) (BCO) . what they mean will now be examined. Opinions These compounds ‘look’ like small cubic diamonds regarding the formation mechanism(s) of meteoritic and lonsdaleite respectively. If these particular and interstellar diamond grains have changed over compounds are suggested as models for diamond the years as new methods of making synthetic nuclei then a number of structural and diamond were developed[1,2]. Meteoritic diamonds thermodynamic predictions can be made about the were once believed to be the result of high pressure - types of diamond that can form and its relative temperature processes in the interior of planetary abundance with regard to the physics and chemistry bodies[3,4]. Impact formation of diamond became of its growth environment. A few examples of this popular after the development of shock wave are: Adamantane is a lower energy form and would diamond synthesis[5] because shock synthesis was tend to form in an environment of sufficient thermal able to form lonsdaleite and meteorites were full of energy to allow the molecule to organize into this lonsdaleite.
    [Show full text]
  • Impact−Cosmic−Metasomatic Origin of Microdiamonds from Kumdy−Kol Deposit, Kokchetav Massiv, N
    11th International Kimberlite Conference Extended Abstract No. 11IKC-4506, 2017 Impact−Cosmic−Metasomatic Origin of Microdiamonds from Kumdy−Kol Deposit, Kokchetav Massiv, N. Kazakhstan L. I. Tretiakova1 and A. M. Lyukhin2 1St. Petersburg Branch Russian Mineralogical Society. RUSSIA, [email protected] 2Institute of remote ore prognosis, Moscow, RUSSIA, [email protected] Introduction Any collision extraterrestrial body and the Earth had left behind the “signature” on the Earth’s surface. We are examining a lot of signatures of an event caused Kumdy-Kol diamond-bearing deposit formation, best- known as “metamorphic” diamond locality among numerous UHP terrains around the world. We are offering new impact-cosmic-metasomatic genesis of this deposit and diamond origin provoked by impact event followed prograde and retrograde metamorphism with metasomatic alterations of collision area rocks that have been caused of diamond nucleation, growth and preserve. Brief geology of Kumdy-Kol diamond-bearing deposit Kumdy-Kol diamond-bearing deposit located within ring structure ~ 4 km diameter, in the form and size compares with small impact crater (Fig. 1). It is important impact event signature. Figure1: Cosmic image of Kumdy-Kol deposit area [http://map.google.ru/]. Diamond-bearing domain had been formed on the peak of UHP metamorphism provoked by comet impact under oblique angle on the Earth surface. As a result, steep falling system of tectonic dislocations, which breakage and fracture zones filling out of impact and host rock breccia with blastomylonitic and blastocataclastic textures have been created. Diamond-bearing domain has complicated lenticular-bloc structure (1300 x 40-200 m size) and lens out with deep about 300 m.
    [Show full text]
  • Handbook of Iron Meteorites, Volume 2 (Canyon Diablo, Part 2)
    Canyon Diablo 395 The primary structure is as before. However, the kamacite has been briefly reheated above 600° C and has recrystallized throughout the sample. The new grains are unequilibrated, serrated and have hardnesses of 145-210. The previous Neumann bands are still plainly visible , and so are the old subboundaries because the original precipitates delineate their locations. The schreibersite and cohenite crystals are still monocrystalline, and there are no reaction rims around them. The troilite is micromelted , usually to a somewhat larger extent than is present in I-III. Severe shear zones, 100-200 J1 wide , cross the entire specimens. They are wavy, fan out, coalesce again , and may displace taenite, plessite and minerals several millimeters. The present exterior surfaces of the slugs and wedge-shaped masses have no doubt been produced in a similar fashion by shear-rupture and have later become corroded. Figure 469. Canyon Diablo (Copenhagen no. 18463). Shock­ The taenite rims and lamellae are dirty-brownish, with annealed stage VI . Typical matte structure, with some co henite crystals to the right. Etched. Scale bar 2 mm. low hardnesses, 160-200, due to annealing. In crossed Nicols the taenite displays an unusual sheen from many small crystals, each 5-10 J1 across. This kind of material is believed to represent shock­ annealed fragments of the impacting main body. Since the fragments have not had a very long flight through the atmosphere, well developed fusion crusts and heat-affected rim zones are not expected to be present. The energy responsible for bulk reheating of the small masses to about 600° C is believed to have come from the conversion of kinetic to heat energy during the impact and fragmentation.
    [Show full text]
  • Evidence from Polymict Ureilite Meteorites for a Disrupted and Re-Accreted Single Ureilite Parent Asteroid Gardened by Several Distinct Impactors
    Available online at www.sciencedirect.com Geochimica et Cosmochimica Acta 72 (2008) 4825–4844 www.elsevier.com/locate/gca Evidence from polymict ureilite meteorites for a disrupted and re-accreted single ureilite parent asteroid gardened by several distinct impactors Hilary Downes a,b,*, David W. Mittlefehldt c, Noriko T. Kita d, John W. Valley d a School of Earth Sciences, Birkbeck University of London, Malet Street, London WC1E 7HX, UK b Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, USA c Mail Code KR, NASA/Johnson Space Center, Houston, TX 77058, USA d Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 W. Dayton St., Madison, WI 53706, USA Received 25 July 2007; accepted in revised form 24 June 2008; available online 17 July 2008 Abstract Ureilites are ultramafic achondrites that exhibit heterogeneity in mg# and oxygen isotope ratios between different meteor- ites. Polymict ureilites represent near-surface material of the ureilite parent asteroid(s). Electron microprobe analyses of >500 olivine and pyroxene clasts in several polymict ureilites reveal a statistically identical range of compositions to that shown by unbrecciated ureilites, suggesting derivation from a single parent asteroid. Many ureilitic clasts have identical compositions to the anomalously high Mn/Mg olivines and pyroxenes from the Hughes 009 unbrecciated ureilite (here termed the ‘‘Hughes cluster”). Some polymict samples also contain lithic clasts derived from oxidized impactors. The presence of several common distinctive lithologies within polymict ureilites is additional evidence that ureilites were derived from a single parent asteroid. In situ oxygen three isotope analyses were made on individual ureilite minerals and lithic clasts, using a secondary ion mass spectrometer (SIMS) with precision typically better than 0.2–0.4& (2SD) for d18O and d17O.
    [Show full text]
  • POSTER SESSION 5:30 P.M
    Monday, July 27, 1998 POSTER SESSION 5:30 p.m. Edmund Burke Theatre Concourse MARTIAN AND SNC METEORITES Head J. W. III Smith D. Zuber M. MOLA Science Team Mars: Assessing Evidence for an Ancient Northern Ocean with MOLA Data Varela M. E. Clocchiatti R. Kurat G. Massare D. Glass-bearing Inclusions in Chassigny Olivine: Heating Experiments Suggest Nonigneous Origin Boctor N. Z. Fei Y. Bertka C. M. Alexander C. M. O’D. Hauri E. Shock Metamorphic Features in Lithologies A, B, and C of Martian Meteorite Elephant Moraine 79001 Flynn G. J. Keller L. P. Jacobsen C. Wirick S. Carbon in Allan Hills 84001 Carbonate and Rims Terho M. Magnetic Properties and Paleointensity Studies of Two SNC Meteorites Britt D. T. Geological Results of the Mars Pathfinder Mission Wright I. P. Grady M. M. Pillinger C. T. Further Carbon-Isotopic Measurements of Carbonates in Allan Hills 84001 Burckle L. H. Delaney J. S. Microfossils in Chondritic Meteorites from Antarctica? Stay Tuned CHONDRULES Srinivasan G. Bischoff A. Magnesium-Aluminum Study of Hibonites Within a Chondrulelike Object from Sharps (H3) Mikouchi T. Fujita K. Miyamoto M. Preferred-oriented Olivines in a Porphyritic Olivine Chondrule from the Semarkona (LL3.0) Chondrite Tachibana S. Tsuchiyama A. Measurements of Evaporation Rates of Sulfur from Iron-Iron Sulfide Melt Maruyama S. Yurimoto H. Sueno S. Spinel-bearing Chondrules in the Allende Meteorite Semenenko V. P. Perron C. Girich A. L. Carbon-rich Fine-grained Clasts in the Krymka (LL3) Chondrite Bukovanská M. Nemec I. Šolc M. Study of Some Achondrites and Chondrites by Fourier Transform Infrared Microspectroscopy and Diffuse Reflectance Spectroscopy Semenenko V.
    [Show full text]
  • Impact Shock Origin of Diamonds in Ureilite Meteorites
    Impact shock origin of diamonds in ureilite meteorites Fabrizio Nestolaa,b,1, Cyrena A. Goodrichc,1, Marta Moranad, Anna Barbarod, Ryan S. Jakubeke, Oliver Christa, Frank E. Brenkerb, M. Chiara Domeneghettid, M. Chiara Dalconia, Matteo Alvarod, Anna M. Fiorettif, Konstantin D. Litasovg, Marc D. Friesh, Matteo Leonii,j, Nicola P. M. Casatik, Peter Jenniskensl, and Muawia H. Shaddadm aDepartment of Geosciences, University of Padova, I-35131 Padova, Italy; bGeoscience Institute, Goethe University Frankfurt, 60323 Frankfurt, Germany; cLunar and Planetary Institute, Universities Space Research Association, Houston, TX 77058; dDepartment of Earth and Environmental Sciences, University of Pavia, I-27100 Pavia, Italy; eAstromaterials Research and Exploration Science Division, Jacobs Johnson Space Center Engineering, Technology and Science, NASA, Houston, TX 77058; fInstitute of Geosciences and Earth Resources, National Research Council, I-35131 Padova, Italy; gVereshchagin Institute for High Pressure Physics RAS, Troitsk, 108840 Moscow, Russia; hNASA Astromaterials Acquisition and Curation Office, Johnson Space Center, NASA, Houston, TX 77058; iDepartment of Civil, Environmental and Mechanical Engineering, University of Trento, I-38123 Trento, Italy; jSaudi Aramco R&D Center, 31311 Dhahran, Saudi Arabia; kSwiss Light Source, Paul Scherrer Institut, 5232 Villigen, Switzerland; lCarl Sagan Center, SETI Institute, Mountain View, CA 94043; and mDepartment of Physics and Astronomy, University of Khartoum, 11111 Khartoum, Sudan Edited by Mark Thiemens, University of California San Diego, La Jolla, CA, and approved August 12, 2020 (received for review October 31, 2019) The origin of diamonds in ureilite meteorites is a timely topic in to various degrees and in these samples the graphite areas, though planetary geology as recent studies have proposed their formation still having external blade-shaped morphologies, are internally at static pressures >20 GPa in a large planetary body, like diamonds polycrystalline (18).
    [Show full text]
  • Three Distinct Torsion Profiles of Electronic Transmission Through
    Three Distinct Torsion Profiles of Electronic Transmission through Linear Carbon Wires Marc H. Garner†, William Bro-Jørgensen, Gemma C. Solomon* Nano-Science Center and Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark. ABSTRACT. The one-dimensional carbon allotrope carbyne, a linear chain of sp-hybridized carbon atoms, is predicted to exist in a polyynic and a cumulenic structure. While molecular forms of carbyne have been extensively characterized, the structural nature is hard to determine for many linear carbon wires that are made in-situ during pulling experiments. Here, we show that cumulenes and polyynes have distinctively different low-bias conductance profiles under axial torsion. We analyze the change of the electronic structure, Landauer transmission, and ballistic current density of the three types of closed-shell molecular carbynes as a function of the torsion angle. Both polyynic, odd-carbon cumulenic, and even-carbon cumulenic carbon wires exhibit helical frontier molecular orbitals when the end-groups are not in a co-planar configuration. This helical conjugation effect gives rise to strong ring current patterns around the linear wires. Only the transmission of even-carbon polyynic wires follows the well-known cosine-squared law with axial torsion that is also seen in biphenyl-type systems. Notably, the transmission of even-carbon cumulenic carbon wires rises with axial torsion from co-planar towards perpendicular orientation of the end-groups. The three distinct transmission profiles of polyynes, odd-carbon cumulenes, 1 and even-carbon cumulenes may allow for experimental identification of the structural nature of linear carbon wires. Their different electron transport properties under axial torsion furthermore underline that, in the molecular limit of carbyne, three different subclasses of linear carbon wires exist.
    [Show full text]
  • Nördlingen 2010: the Ries Crater, the Moon, and the Future of Human Space Exploration, P
    Program and Abstract Volume LPI Contribution No. 1559 The Ries Crater, the Moon, and the Future of Human Space Exploration June 25–27, 2010 Nördlingen, Germany Sponsors Museum für Naturkunde – Leibniz-Institute for Research on Evolution and Biodiversity at the Humboldt University Berlin, Germany Institut für Planetologie, University of Münster, Germany Deutsches Zentrum für Luft- und Raumfahrt DLR (German Aerospace Center) at Berlin, Germany Institute of Geoscience, University of Freiburg, Germany Lunar and Planetary Institute (LPI), Houston, USA Deutsche Forschungsgemeinschaft (German Science Foundation), Bonn, Germany Barringer Crater Company, Decatur, USA Meteoritical Society, USA City of Nördlingen, Germany Ries Crater Museum, Nördlingen, Germany Community of Otting, Ries, Germany Märker Cement Factory, Harburg, Germany Local Organization City of Nördlingen Museum für Naturkunde – Leibniz- Institute for Research on Evolution and Biodiversity at the Humboldt University Berlin Ries Crater Museum, Nördlingen Center of Ries Crater and Impact Research (ZERIN), Nördlingen Society Friends of the Ries Crater Museum, Nördlingen Community of Otting, Ries Märker Cement Factory, Harburg Organizing and Program Committee Prof. Dieter Stöffler, Museum für Naturkunde, Berlin Prof. Wolf Uwe Reimold, Museum für Naturkunde, Berlin Dr. Kai Wünnemann, Museum für Naturkunde, Berlin Hermann Faul, First Major of Nördlingen Prof. Thomas Kenkmann, Freiburg Prof. Harald Hiesinger, Münster Prof. Tilman Spohn, DLR, Berlin Dr. Ulrich Köhler, DLR, Berlin Dr. David Kring, LPI, Houston Dr. Axel Wittmann, LPI, Houston Gisela Pösges, Ries Crater Museum, Nördlingen Ralf Barfeld, Chair, Society Friends of the Ries Crater Museum Lunar and Planetary Institute LPI Contribution No. 1559 Compiled in 2010 by LUNAR AND PLANETARY INSTITUTE The Lunar and Planetary Institute is operated by the Universities Space Research Association under a cooperative agreement with the Science Mission Directorate of the National Aeronautics and Space Administration.
    [Show full text]
  • On the Road to Carbene and Carbyne Complexes
    ON THE ROAD TO CARBENE AND CARBYNE COMPLEXES Nobel Lecture, 11 December 1973 by ERNST OTTO FISCHER Inorganic Chemistry Laboratory, Technical University, Munich, Federal Republic of Germany Translation from the German text INTRODUCTION In the year 1960, I had the honour of giving a talk at this university* about sandwich complexes on which we were working at that time. I think I do not have to repeat the results of those investigations today. I would like to talk instead about a field of research in which we have been intensely interested in recent years: namely, the field of carbene complexes and, more recently, carbyne complexes. If we substitute one of the hydrogen atoms in a hydrocarbon of the alkane type - for example, ethane - by a metal atom, which can of course bind many more ligands, we arrive at an organometallic compound in which the organic radical is bound to the metal atom by a σ-bond (Fig. la). The earliest compounds of this kind were prepared more than a hundred years ago; the first was cacodyl, prepared by R. Bunsen (1), and then zinc dialkyls were prepared by E. Frankland (2). Later V. Grignard was able to synthesise alkyl magnesium halides by treating magnesium with alkyl halides (3). Grignard was awarded the Nobel Prize in 1912 for this effort. We may further recall the organo-aluminium compounds (4) of K. Ziegler which form the basis for the low pressure polymerisation, for example of ethylene. Ziegler and G. Natta were together honoured with the Nobel Prize in 1963 for their work on organometallic compounds.
    [Show full text]
  • Asteroid Impacts on Earth Make Structurally Bizarre Diamonds 21 November 2014, by Robert Burnham
    Asteroid impacts on Earth make structurally bizarre diamonds 21 November 2014, by Robert Burnham "So-called lonsdaleite is actually the long-familiar cubic form of diamond, but it's full of defects," says Péter Németh. These can occur, he explains, due to shock metamorphism, plastic deformation or unequilibrated crystal growth. The lonsdaleite story began almost 50 years ago. Scientists reported that a large meteorite, called Canyon Diablo after the crater it formed on impact in northern Arizona, contained a new form of diamond with a hexagonal structure. They described it as an impact-related mineral and called it lonsdaleite, after Dame Kathleen Lonsdale, a famous crystallographer. Since then, "lonsdaleite" has been widely used by scientists as an indicator of ancient asteroidal Diamond grains from the Canyon Diablo meteorite. The impacts on Earth, including those linked to mass tick marks are spaced one-fifth of a millimeter (200 extinctions. In addition, it has been thought to have microns) apart. Credit: Arizona State mechanical properties superior to ordinary University/Laurence Garvie diamond, giving it high potential industrial significance. All this focused much interest on the mineral, although pure crystals of it, even tiny ones, have never been found or synthesized. That posed (Phys.org) —Scientists have argued for half a a long-standing puzzle. century about the existence of a form of diamond called lonsdaleite, which is associated with impacts by meteorites and asteroids. A group of scientists based mostly at Arizona State University now show that what has been called lonsdaleite is in fact a structurally disordered form of ordinary diamond.
    [Show full text]
  • Novel Superhard Carbon: C-Centered Orthorhombic C8
    week ending PRL 107, 215502 (2011) PHYSICAL REVIEW LETTERS 18 NOVEMBER 2011 Novel Superhard Carbon: C-Centered Orthorhombic C8 Zhisheng Zhao,1 Bo Xu,1 Xiang-Feng Zhou,2 Li-Min Wang,1 Bin Wen,1 Julong He,1 Zhongyuan Liu,1 Hui-Tian Wang,2 and Yongjun Tian1,* 1State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China 2School of Physics and Key Laboratory of Weak-Light Nonlinear Photonics, Ministry of Education, Nankai University, Tianjin 300071, China (Received 10 June 2011; published 14 November 2011) A novel carbon allotrope of C-centered orthorhombic C8 (Cco-C8) is predicted by using a recently 3 developed particle-swarm optimization method on structural search. Cco-C8 adopts a sp three- dimensional bonding network that can be viewed as interconnected ð2; 2Þ carbon nanotubes through 4- and 6-member rings and is energetically more favorable than earlier proposed carbon polymorphs (e.g., M carbon, bct-C4, W carbon, and chiral C6) over a wide range of pressures studied (0–100 GPa). The simulated x-ray diffraction pattern, density, and bulk modulus of Cco-C8 are in good accordance with the experimental data on structurally undetermined superhard carbon recovered from cold compression of carbon nanotube bundles. The simulated hardness of Cco-C8 can reach a remarkably high value of 95.1 GPa, such that it is capable of cracking diamond. DOI: 10.1103/PhysRevLett.107.215502 PACS numbers: 61.50.Ks, 61.48.De, 64.60.My Carbon possesses the unique capability to form sp-, synthesized under nonhydrostatic stress conditions sp2-, and sp3-hybridized bonds, yielding various allo- [11,12].
    [Show full text]
  • Calcium-Decorated Carbyne Networks As Hydrogen Storage Media † || † || ‡ † § † Pavel B
    LETTER pubs.acs.org/NanoLett Calcium-Decorated Carbyne Networks as Hydrogen Storage Media † || † || ‡ † § † Pavel B. Sorokin, , Hoonkyung Lee, , Lyubov Yu. Antipina, Abhishek K. Singh, , and Boris I. Yakobson*, † Department of Mechanical Engineering and Materials Science, Department of Chemistry, and the Smalley Institute for Nanoscale Science and Technology, Rice University, Houston, Texas 77005, United States ‡ Technological Institute of Superhard and Novel Carbon Materials, Troitsk, Moscow District, 142190, Russian Federation § Materials Research Centre Indian Institute of Science, Bangalore 560012 India ABSTRACT: Among the carbon allotropes, carbyne chains appear outstand- ingly accessible for sorption and very light. Hydrogen adsorption on calcium- decorated carbyne chain was studied using ab initio density functional calculations. The estimation of surface area of carbyne gives the value four times larger than that of graphene, which makes carbyne attractive as a storage scaffold medium. Furthermore, calculations show that a Ca-decorated carbyne can adsorb up to 6 H2 molecules per Ca atom with a binding energy of ∼0.2 eV, desirable for reversible storage, and the hydrogen storage capacity can exceed ∼8 wt %. Unlike recently reported transition metal-decorated carbon nanostructures, which suffer from the metal clustering diminishing the storage capacity, the clustering of Ca atoms on carbyne is energetically unfavorable. Thermodynamics of adsorption of H2 molecules on the Ca atom was also investigated using equilibrium grand partition function. KEYWORDS: Carbyne, carbon chain, calcium, hydrogen storage, density functional theory biquitous carbon allotropes can be ranked by the coordina- atoms in such organometallic complexes play the main role of Ution number of their structures, the number of nearest neigh- adsorbing hydrogen molecules, whereas the graphitic materials serve bors to each C atom, as diamond, graphite, nanotubes and fullerenes, as host for them.
    [Show full text]