DOCSLIB.ORG

Scanning Near-Field Optical Lithography and Microscopy of Conjugated Polymer Structures

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Scanning Near-Field Optical Lithography and Microscopy of Conjugated Polymer Structures Scanning Near-Field Optical Lithography and Microscopy of Conjugated Polymer Structures Oliver Fenwick University College London 2007 i A dissertation submitted for the degree of Doctor of Philosophy UMI Number: U592766 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI U592766 Published by ProQuest LLC 2013. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 I would like to thank everyone I’ve worked with during the course of this degree. It’s been a very enjoyable experience despite the darkness in the SNOM lab! In particular I would like to thank Andy, Lisa, Antonio and Vlad for helping to get things going in the early days, and of those who I worked with later on I owe a lot to Dan, Gianluca, Soumaya and Laurent. Of course, the most thanks goes to my supervisor, Franco, who has provided knowledge, ideas and equipment through all the stages of the degree and has found numerous excuses to send me to Italy (!). Financial support was from EPSRC (with a top-up from Mum and Dad during the write-up period). Finally, Jennie has been very patient with me and the typos in early drafts of this thesis: an excellent proof reader and an even better girlfriend! I, Oliver Fenwick, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. Abstract This thesis is concerned with the use of the scanning near-field optical microscope (SNOM) to pattern and image conjugated polymer structures. The SNOM is one of just a few optical instruments which are capable of breaking the diffraction limit which limits conventional microscopes to a resolution of approximately half a wavelength. It does so by directing light onto a sub-wavelength aperture at the apex of a probe, establishing a local evanescent field of subwavelength dimensions around the aperture. Conjugated polymers on the other hand are an interesting class of materials which have semiconducting properties and a rich photophysics making them suitable for use in novel light-emitting diodes, transistors and solar cells. I demonstrate direct patterning of several conjugated polymers using the SNOM with a resolution extending below 100 nm and attempt to explain the resolution of the lithography through simulations using the Bethe-Bouwkamp model of the field surrounding a sub-wavelength aperture. In particular the modelling focuses on the role of the film thickness and reflections from the substrate. Further experiments demonstrate that thermal effects which can be caused by heating of the SNOM probe do not play a role in lithography with the SNOM in this case. However, I demonstrate the use of a scanning thermal microscope to do a novel and purely thermal lithography on one of the same conjugated polymers. Resolutions of 120 nm are demonstrated, and finite element analysis is used to show that significant improvements in resolution should be possible by optimisation of the probe and the polymer film. In addition, I present simulations of imaging artefacts caused by topography on samples under SNOM investigation, and use the same model to look at the potential of the SNOM to obtain information about sub-surface objects. SNOM images are presented of blends and supramolecular fibres of conjugated polymers. 3 Contents 1. Overview........................................................................................................................................ 11 2. Exploiting the optical near-field..............................................................................................13 2.1 Implementations of near-field microscopy ........................................................................19 2.1.1 Scanning probe microscopy ................................................................................................ 20 2.1.2 Near-field probe design and manufacture ........................................................................... 21 2.1.3 Shear-force feedback ........................................................................................................... 23 2.1.4 Implementations of SNOM and recent developments .........................................................25 2.2 Theoretical description of the near-field ............................................................................28 2.2.1 The Bethe-Bouwkamp model of the near-field from a circular aperture ............................. 28 2.2.2 Other models of the near-field ............................................................................................ 30 3. SNOM apparatus specific to this thesis............................................................................... 32 3.1 SNOM hardware ...................................................................................................................32 3.2 Probes ..................................................................................................................................... 36 4. Overview of conjugated polymers and their devices .........................................................38 4.1 Optical Properties of conjugated polymers ........................................................................ 40 4.2 Optoelectronic conjugated polymer devices ......................................................................45 4.2.1. Polymer light-emitting diodes .............................................................................................. 45 4.2.2. Photovoltaics ........................................................................................................................ 47 4.2.3. Bilayer and blended devices ................................................................................................ 48 5. Scanning near-field optical lithography (SNOL) of conjugated polymers.................51 5.1 Introduction to scanning near-field optical lithography (SNOL) ...................................51 5.1.1. Achievable resolution of SNOL .......................................................................................... 52 5.1.2. Aspect ratio of structures produced by SNOL .................................................................... 54 5.1.3. Apertured vs. Apertureless SNOL ....................................................................................... 55 5.1.4. Patterning of functional materials by SNOL ....................................................................... 56 5.2 Scanning near-field optical lithography of conjugated polymers ..................................58 5.2.1. SNOL of poly(p-phenylene vinylene) .................................................................................58 5.2.2. SNOL of r-F80x and r-BTOx ..............................................................................................61 5.3 Modelling the Resolution of SNOL .................................................................................. 67 5.3.1 Model of a lithographic point ..............................................................................................67 5.3.2 Role of substrate reflections in near-field lithography of thin films ....................................68 5.3.3 Achieving maximum resolution with SNOL ...................................................................... 76 5.4 Probe heating effects during SNOL ................................................................................... 77 5.4.1. Indirect measurement of sample heating in SNOM by thermochromism in PPV ................78 5.4.2. Shape-dependent thermal expansion effects in apertured SNOM probes .............................83 6. Modelling the near-field for imaging ....................................................................................92 6.1 Simulation of artifacts in SNOM images ...........................................................................92 6.2 Investigation of buried structures using the SNOM .......................................................100 6.2.1 Imaging of slanted heterojunctions ....................................................................................100 6.2.2 Imaging of buried objects .................................................................................................. 106 7 Lithography of a conjugated polymer with a microthermal probe ............................ 109 7.1 Background and motivations .............................................................................................109 7.2 System overview ..................................................................................................................I l l 4 7.3 Experimental results............................................................................................................112 7.3.1 Effect of exposure time ....................................................................................................... 113 7.3.2 Thermomechanical effects ..................................................................................................117 7.4 Modelling the temperature
Load more

Recommended publications
  • Methods for Topography Artifacts Compensation in Scanning Thermal Microscopy
    Ultramicroscopy 155 (2015) 55–61 Contents lists available at ScienceDirect Ultramicroscopy journal homepage: www.elsevier.com/locate/ultramic Methods for topography artifacts compensation in scanning thermal microscopy Jan Martinek a,c,n, Petr Klapetek a,b, Anna Charvátová Campbell a a Czech Metrology Institute, Okružní 31, 638 00 Brno, Czech Republic b CEITEC, BUT, Technická 3058/10, 616 00 Brno, Czech Republic c Department of Physics, Faculty of Civil Engineering, BUT, Žižkova 17, Brno 602 00, Czech Republic article info abstract Article history: Thermal conductivity contrast images in scanning thermal microscopy (SThM) are often distorted by Received 10 July 2014 artifacts related to local sample topography. This is pronounced on samples with sharp topographic Received in revised form features, on rough samples and while using larger probes, for example, Wollaston wire-based probes. The 8 April 2015 topography artifacts can be so high that they can even obscure local thermal conductivity variations Accepted 15 April 2015 influencing the measured signal. Three methods for numerically estimating and compensating for to- Available online 25 April 2015 pographic artifacts are compared in this paper: a simple approach based on local sample geometry at the Keywords: probe apex vicinity, a neural network analysis and 3D finite element modeling of the probe–sample Scanning thermal microscopy interaction. A local topography and an estimated probe shape are used as source data for the calculation Artifacts in all these techniques; the result is a map of false conductivity contrast signals generated only by sample Neural networks topography. This map can be then used to remove the topography artifacts from measured data or to estimate the uncertainty of conductivity measurements using SThM.
    [Show full text]
  • Fabrication of Hot-Wire Probes and Electronics for Constant Temperature Anemometers
    Latin American Applied Research 40:233-239(2010) FABRICATION OF HOT-WIRE PROBES AND ELECTRONICS FOR CONSTANT TEMPERATURE ANEMOMETERS O.D. OSORIO †, N. SILIN ‡ and J. CONVERTI § † Instituto Balseiro, S. C. de Bariloche, 8400, Argentina, e-mail: [email protected] ‡ Investigador CONICET, Instituto Balseiro, S. C. de Bariloche, 8400, Argentina, e-mail: [email protected] r § Instituto Balseiro, S. C. de Bariloche, 8400, Argentina, e-mail: [email protected] r Abstract −−−−−− The purpose of this paper is to discuss rior removal of the silver by chemical etching. the construction of constant temperature hot wire Electronics were built following the design of Its- anemometers. Different options are analyzed for the weire and Helland (1983) but including modifications to fabrication of sensors and electronics. A practical avoid the use of components not readily available, like and simple method is developed to manufacture the variable inductors and delay lines. probe and associated electronics. The fabricated sen- Frequency response was measured as suggested by sor has a diameter of 2 µm and approximately 500 Freymuth (1977) and Fingerson (1994). Measurements µm in length. The associated electronics are designed of a turbulent flow field were performed simultaneously to keep the sensor working at a constant tempera- with the present electronics and a commercial unit ture and allow the indirect measurement of speed. (TSI1051). The two measurements were equivalent for The design is simple, inexpensive and highly flexible frequencies up to approximately 50 kHz. regarding its use and modifications. The dynamic II. PROBE CONSTRUCTION tests performed and the comparison with a commer- Hot-wire probes are built with a thin wire of 0.5 to 20 cial model shows a satisfactory performance.
    [Show full text]
  • (12) United States Patent (10) Patent No.: US 8,177,422 B2 Kjoller Et Al
    US008177422B2 (12) United States Patent (10) Patent No.: US 8,177,422 B2 Kjoller et al. (45) Date of Patent: May 15, 2012 (54) TRANSITION TEMPERATURE (56) References Cited MICROSCOPY U.S. PATENT DOCUMENTS (75) Inventors: Kevin Kjoller, Santa Barbara, CA (US); 6,185.992 B1* 2/2001 Daniels et al. ................ 25O?307 Khoren Sahagian, Burbank, CA (US); 6,200,022 B1* 3/2001 Hammiche et al. ............. 374/46 Doug Gotthard, Carpinteria, CA (US); gig3. R : S383 Airectalammiche et al. .............. (92.i Althy E" E. EcA 6,805,839 B2 * 10/2004 Cunningham et al. ... 422/82. 12 (US); Craig Prater, Santa Barbara, 7,448,798 B1 * 1 1/2008 Wang ..................... ... 374f183 (US); Roshan Shetty, Westlake Village, 2002/O126732 A1* 9, 2002 Shakouri et al. .............. 374,130 CA (US); Michael Reading, Norwich 2002/0196834 A1* 12/2002 Zaldivar et al. ................. 374,22 (GB) 2004/0026007 A1 2/2004 Hubert et al. ................... 156,64 2004/0202226 A1* 10, 2004 Gianchandani et al. ...... 374,185 2005/0105097 A1* 5/2005 Fang-Yen et al. ... 356,497 (73) Assignee: Anasys Instruments, Santa Barbara, CA 2006/0243034 A1 ck 11, 2006 Chand et al. T3/104 (US) 2007/0263696 A1* 11/2007 Kjoller et al. 374/31 2009 OO32706 A1* 2, 2009 Prater et al. 25O?307 (*) Notice: Subject to any disclaimer, the term of this 2009/0229020 A1* 9, 2009 Adams et al. ................... 850/33 patent is extended or adjusted under 35 SR A. 1939 CC. C. al . 3. U.S.C. 154(b) by 474 days. 2011/0078834 A1* 3/2011 King ................................
    [Show full text]
  • Pv-3 Globar Sensing Element
    Lawrence Berkeley National Laboratory Recent Work Title VAPOR-LIQUID EQUILIBRIA IN THE SYSTEM HYDROGEN-NITROGEN Permalink https://escholarship.org/uc/item/836767dh Author Maimoni, Arturo. Publication Date 1955-09-01 eScholarship.org Powered by the California Digital Library University of California UCRL 3/3 I \ UNIVERSITY OF CALIFORNIA TWO-WEEK LOAN COPY This is a library Circulating Copy which may be borrowed for two weeks. For a personal retention copy, call Tech. Info. Diuision, Ext. 5545 BERKELEY. CALIFORNIA DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. UCRL-3131 UNIVERSITY OF CALIFORNIA I Radiation Laboratory Berkeley,. California Contract No. W -7405 -eng-48 . VAPOR-LIQUID EQUILIBRIA IN THE SYSTEM HYDROGEN -NITROGEN Arturo M.a.imoni (The sis) September 1, 1955 .·• Printed for the U.
    [Show full text]
  • Advances in Scanning Thermal Microscopy Measurements for Thin Films
    Chapter 1 Advances in Scanning Thermal Microscopy Measurements for Thin Films Liliana Vera-Londono, Olga Caballero-Calero, Jaime Andrés Pérez-Taborda and Marisol Martín-González Additional information is available at the end of the chapter http://dx.doi.org/10.5772/intechopen.79961 Abstract One of the main challenges nowadays concerning nanostructured materials is the under- standing of the heat transfer mechanisms, which are of the utmost relevance for many specific applications. There are different methods to characterize thermal conductivity at the nanoscale and in films, but in most cases, metrology, good resolution, fast time acquisition, and sample preparation are the issues. In this chapter, we will discuss one of the most fascinating techniques used for thermal characterization, the scanning thermal microscopy (SThM), which can provide simultaneously topographic and thermal infor- mation of the samples under study with nanometer resolution and with virtually no sample preparation needed. This method is based on using a nanothermometer, which can also be used as heater element, integrated into an atomic force microscope (AFM) cantilever. The chapter will start with a historical introduction of the technique, followed by the different kinds of probes and operation modes that can be used. Then, some of the equations and heating models used to extract the thermal conductivity from these mea- surements will be briefly discussed. Finally, different examples of actual measurements performed on films will be shown. Most of these results deal with thermoelectric thin films, where the thermal conductivity characterization is one of the most important parameters to optimize their performance for real applications. Keywords: scanning thermal microscopy, thermal probes, thermoelectric thin films, thermal conductivity, local temperature measurements © 2018 The Author(s).
    [Show full text]
  • High-Frequency Voltage Measurements
    REPORT CRPL-8-2 ISSUED APRIL 14, 1948 tiona! Bureau of Standards Library, N. W. Bldg. Mm/ , c 1Q/iq U. S. DEPARTMENT OF COMMERCE NOV 1 b 1949 NATIONAL BUREAU OF STANDARDS CENTRAL RADIO PROPAGATION LABORATORY WASHINGTON, D. C. HIGH - FREQUENCY VOLTAGE MEASUREMENTS BY M. C. SELBY Report No, NATIONAL BUREAU OF STANDARDS CRPL-8-2. CENTRAL RADIO PROPAGATION LABORATORY WASHINGTON 25, D. C. HIGH-FREQUENCY VOLTAGE MEASUREMENTS By M, C. Selby Preface This report on r-f measurements contains material written for inclusion in a Handbook of Physical Measurements to be published by the National Bureau of Stand¬ ards . The objectives ares (l) to present an up-to-date conspectus of fundamental techniques used in scientific research, laboratory and commercial measurements as well as their relative merits, (2) to cover all principles and methods that have met with any degree of success but not necessarily to compile all available material in encyclopedical form, (3) to meet the need of the professional worker and graduate student somewhat more comprehensively than the presently available handbooks do, A considerable amount of the material presented is based on work done at this Bureau, Bibliography is omitted because the references given leading in turn to further references and bibliography are considered adequate. Recognition and thanks are due to the authors listed in the references for their kind permission to quote some of these data and reproduce some drawings and curves, as well as to the N. B. S, editorial readers for valuable suggestions and cooperation. Contents Preface List of figures Introductory note 1, Accurate high-precision methods based on d-c measurements (a) Power measurements (b) Current meter and resistance (c) Cathode-ray beam deflection (d) Electrostatic voltmeter 2, Accurate moderate precision methods (a) Vacuum tube voltmeter (b) Non-thermionic rectifiers 3, Pulse-peak voltage measurement (a) Cathode-ray deflection (b) Diode peak voltmeters (o've r) 4.
    [Show full text]
  • Nano-Scale Lithography and Microscopy of Organic Semiconductors
    Nano-scale Lithography and Microscopy of Organic Semiconductors Dan Credgington University College London, 2010 A dissertation submitted for the degree of Doctor of Philosophy Acknowledgements Over the (long!) years of this degree, I‟ve been very fortunate to work with some wonderful and talented people; in particular I‟d like to thank Lisa, Gustaf, Mar, Laurent and all the various denizens of the LCN for providing not only a stimulating scientific environment, but also some light relief from the dark of the SNOM lab. I especially want to thank Olly, for spending so much time in it with me, and keeping me sane throughout. My biggest thanks go to Franco, for his experience, support, ideas and patience, not to mention the many excuses he found to fund my trips to conferences, workshops and schools. Finally I‟d like to thank my parents, and especially Claire, for supporting me unwaveringly for so long, and pushing me to finish the job. For this and more I am truly grateful. I, Dan Credgington confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. 2 Abstract The development of organic electronic and photonic devices increasingly requires the development of micro- and nano-structured morphologies, which in turn require the development of both prototyping and scalable patterning methods. This thesis presents investigations which explore and develop unconventional patterning techniques for a variety of conjugated polymers and organic molecules, using scanning near-field optical lithography (SNOL), scanning thermal lithography (SThL) and molecular self-assembly.
    [Show full text]
  • Transition Regime Heat Conduction of Argon/Hydrogen and Xenon/Hydrogen
    TRANSITION REGIME HEAT CONDUCTION OF ARGON/HYDROGEN AND XENON/HYDROGEN MIXTURES IN A PARABOLIC TROUGH RECEIVER by FRANK W. BURKHOLDER B.S., Stanford University, l995 M.S., University of Wisconsin, Madison, 2004 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirement for the degree of Doctor of Philosophy Department of Civil, Environmental, and Architectural Engineering 2011 TRANSITION REGIME HEAT CONDUCTION OF ARGON/HYDROGEN AND XENON/HYDROGEN MIXTURES IN A PARABOLIC TROUGH RECEIVER This thesis entitled: Transition Regime Heat Conduction of Argon/Hydrogen and Xenon/Hydrogen Mixtures in a Parabolic Trough Receiver by Frank W. Burkholder has been approved for the Department of Civil, Environmental, and Architectural Engineering Dr. Michael Brandemuehl Dr. Chuck Kutscher Dr. Moncef Krarti Dr. Harihar Rajaram Dr. Ed Wolfrum Date The final copy of this thesis has been examined by the signatories, and we Find that both the content and the form meet acceptable presentation standards Of scholarly work in the above mentioned discipline. Burkholder, Frank W. (Ph.D., Civil, Environmental, and Architectural Engineering) Transition Regime Heat Conduction of Argon/Hydrogen and Xenon/Hydrogen Mixtures in a Parabolic Trough Receiver Thesis directed by Professor Michael Brandemuehl ABSTRACT The annulus of a parabolic trough receiver is normally evacuated to prevent heat conduction between the internal absorber pipe and the external glass envelope. In the past, this vacuum has been compromised by hydrogen permeation from the heat transfer fluid through the absorber pipe. Heat conduction is significantly increased by the presence of hydrogen in the annulus even though its final pressure – 10 to 100 Pa – is sufficiently low that the thermal conductivity and temperature difference alone cannot predict it.
    [Show full text]
  • Imaging of Local Thermal and Electrical Conductivity with Scanning Force Microscopy
    Scanning Microscopy Volume 8 Number 2 Article 4 7-30-1994 Imaging of Local Thermal and Electrical Conductivity with Scanning Force Microscopy M. Maywald Bergische Universität Wuppertal R. J. Pylkki TopoMetrix, Santa Clara L. J. Balk Bergische Universität Wuppertal Follow this and additional works at: https://digitalcommons.usu.edu/microscopy Part of the Biology Commons Recommended Citation Maywald, M.; Pylkki, R. J.; and Balk, L. J. (1994) "Imaging of Local Thermal and Electrical Conductivity with Scanning Force Microscopy," Scanning Microscopy: Vol. 8 : No. 2 , Article 4. Available at: https://digitalcommons.usu.edu/microscopy/vol8/iss2/4 This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Scanning Microscopy by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. Scanning Microscopy, Vol. 8, No. 2, 1994 (Pages 181-188) 0891-7035 /94$5. 00 +. 25 Scanning Microscopy International, Chicago (AMF O'Hare), IL 60666 USA IMAGING OF LOCAL THERMAL AND ELECTRICAL CONDUCTIVITY WITH SCANNING FORCE l\fiCROSCOPY M. Maywald, R.J. Pylkki 1, and L.J. Ball/ Bergische Universitiit Wuppertal, Lehrstuhl fiir Elektronik, D-42097 Wuppertal, Germany 1TopoMetrix, 5403 Betsy Ross Dr., Santa Clara, CA 95054-1162, U.S.A. (Received for publication March 6, 1994 and in revised form July 30, 1994) Abstract Introduction The evaluation of thermal and electrical properties Since the scanning force microscope (SFM) has has been demonstrated using a scanning force micro­ been invented [1] many different applications have been scope under ambient air condition.
    [Show full text]
  • Numerical and Experimental Investigations of Self-Heating Phenomena in 3D Hybrid Bonding Imaging Technologies Axel Pic
    Numerical and experimental investigations of self-heating phenomena in 3D Hybrid Bonding imaging technologies Axel Pic To cite this version: Axel Pic. Numerical and experimental investigations of self-heating phenomena in 3D Hybrid Bond- ing imaging technologies. Thermics [physics.class-ph]. Université de Lyon, 2019. English. NNT : 2019LYSEI054. tel-02956242 HAL Id: tel-02956242 https://tel.archives-ouvertes.fr/tel-02956242 Submitted on 2 Oct 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. N° d’ordre NNT : 2019LYSEI054 THESE de DOCTORAT DE L’UNIVERSITE DE LYON Opérée au sein de L’INSA de Lyon En cotutelle internationale avec STMicroelectronics Ecole Doctorale N° ED 162 MEGA de Lyon Energétique/Thermique Soutenue publiquement le 04/09/2019, par : Axel PIC Numerical and experimental investigations of self-heating phenomena in 3D Hybrid Bonding imaging technologies Devant le jury composé de : VAILLON Rodolphe Directeur de recherche (IES) Directeur de thèse CHAPUIS Pierre-Olivier Chargé de recherche (CETHIL) Co-directeur de thèse GALLOIS-GARREIGNOT
    [Show full text]
  • Apparatus for the Study of Rayleigh-Benard Convection In
    Apparatus for the study of Rayleigh-B´enard convection in gases under pressure John R. de Bruyn Department of Physics Memorial University of Newfoundland St. John's, Newfoundland, Canada A1B 3X7 Eberhard Bodenschatz Department of Physics and Laboratory of Atomic and Solid State Physics Cornell University Ithaca, New York 14853 Stephen W. Morris Department of Physics and Erindale College University of Toronto 60 St. George St., Toronto, Ontario, Canada M5S 1A7 Steven P. Trainoff Department of Physics and Center for Nonlinear Science University of California Santa Barbara, California 93106-9530 Yuchou Hu Department of Physics and Center for Nonlinear Science University of California Santa Barbara, California 93106-9530 and Center for Nonlinear Studies and Material Science and Technology Division Los Alamos National Laboratory Los Alamos, New Mexico 87545 David S. Cannell and Guenter Ahlers Department of Physics and Center for Nonlinear Science University of California Santa Barbara, California 93106-9530 (April 10, 2002) We review the history of experimental work on Rayleigh-B´enard convection in gases, and then describe a modern apparatus which has been used in our experiments on gas convection. This system allows the study of patterns in a cell with an aspect ratio (cell radius/fluid layer depth) as large as 100, with the cell thickness uniform to a fraction of a µm, and with the pressure controlled at the level of one part in 105. This level of control can yield a stability of the critical temperature difference for the convective onset of better than one part in 104. The convection patterns are visualized and the temperature field can be inferred using the shadowgraph technique.
    [Show full text]
  • Measurements of Freestream Fluctuations in the NASA Langley 20-Inch Mach 6 Tunnel
    Measurements of Freestream Fluctuations in the NASA Langley 20-Inch Mach 6 Tunnel Amanda Chou∗ NASA Langley Research Center, Hampton, VA 23681, USA Andrew N. Leidy† Texas A&M University, College Station, TX 77843, USA Brett F. Bathel,‡ Rudolph A. King,§ and Gregory C. Herring¶ NASA Langley Research Center, Hampton, VA 23681, USA An experimental campaign was conducted to measure and to characterize the freestream disturbance levels in the NASA Langley Research Center 20-Inch Mach 6 Wind Tunnel. A pitot rake was instrumented with fast pressure transducers, hot wires, and an atomic layer thermopile to quantify the fluctuation levels of pressure, mass flux, and heat flux, respectively. In conjunction with these probe-based measurements, focused laser differen- tial interferometry was used to optically measure density fluctuations. Measurements were made at five nominal different unit Reynolds numbers ranging from 3.28{26.5×106/m. The rake was positioned at two different streamwise locations and several different roll angles to measure flow uniformity within the test section. In general, noise levels were spatially consistent within the tested region. Pitot pressure fluctuation levels ranged from 0.84% at the highest Reynolds number tested to 1.89% at the lowest Reynolds number tested. Freestream mass-flux fluctuations remained relatively constant between 1.8{2.5% of the freestream. The pressure transducers were also used to determine the dominant disturbance speed and angle of propagation. The disturbances were estimated to travel at approximately 54{81% of the freestream speed at an angle of approximately 21{44° from the freestream direction, but these measurements had a significant amount of uncertainty.
    [Show full text]