Bulletin of the American Physical Society
2010 Annual Meeting of the California-Nevada Section of the APS
Volume 55, Number 12
Friday–Saturday, October 29–30, 2010; Pasadena, California
Session D1: Condensed Matter Physics and Materials Science II |
Hide Abstracts |
Chair: Uwe Bergmann, SLAC National Accelerator Lab Room: Building 74 - Beckman Institute Auditorium |
Friday, October 29, 2010 4:00PM - 4:12PM |
D1.00001: Crystallization of Solids in the Presence of Anisotropic Growth Rates and Gaussian Nucleation Rates Kimberly Lokovic, Andreas Bill, Ralf Bergmann The grain size distribution allows characterizing quantitatively the microstructure of an amorphous solid at different stages of crystallization. We review the theory developed recently for the grain size distribution (GSD) [1] and present two extensions of the model. In the first generalization, we replace the isotropic growth rate by an anisotropic rate that leads to the formation of ellipsoidal grains. Different anisotropic growth mechanisms are considered. We obtain an analytical expression for the GSD when the growth rate leads to a change of volume leaving the shape of grains invariant [2]. In the second generalization, we study how the GSD is affected by replacing the Dirac-type source term of nuclei by a more physical Gaussian-type source. We use that model to analyze the GSD at early stages of crystallization.\\[4pt] [1] A.V.Teran, R.B.Bergmann and A.Bill, Phys. Rev. B 81, 075319 (2010).\\[0pt] [2] K.S.Lokovic, R.B.Bergmann and A.Bill, Mater. Res. Soc. Symp. Proc. 1245, A16-07 (2010). [Preview Abstract] |
Friday, October 29, 2010 4:12PM - 4:24PM |
D1.00002: Self Assembly of CdSe Quantum Dots in Cholesteric Liquid Crystal Andrea Rodarte Controlled self assembly of quantum dots (QDs) over macroscopic scales is important to realizing the potential for new optical applications. Here we suspend CdSe quantum dots in a cholesteric liquid crystal and investigate the ordering of the QDs when loaded into a Grandjean-Cano wedge cell. We use polarized optical microscopy and scanning microscopy photoluminescence measurements to obtain information about the dispersion and emission of the QDs. We find that the wavelength and intensity of the polarized QD emission is modulated by the Grandjean steps of the liquid crystal texture. These results demonstrate how the LC texture can affect the arrangement and emission of the QD nanoparticles. [Preview Abstract] |
Friday, October 29, 2010 4:24PM - 4:36PM |
D1.00003: Studies of Melamine Under Extreme Conditions Martin Galley, Michael Pravica, Changyong Park We performed two synchrotron-based x-ray diffraction studies on melamine at high pressures and at variable temperatures. The first study utilized ``white'' x-ray beams to perform energy-dispersive x-ray diffraction at high pressure and high temperature. Pressure was generated using a Paris-Edinburgh Cell to employ larger sample volumes for improved signal to noise from weakly scattering organic samples such as melamine. High temperatures were created using a resistive/graphitic cup surrounding the sample under pressure. The PT phase diagram was explored by first pressurizing the sample to 3.5 GPa at room temperature and then resistively heating it up to 1197 K. Above 4.85 GPa and 967 K, an irreversible phase transition was observed. For the second study, we used monochromatic x-ray radiation to study melamine at high pressure and ambient temperature using angular-dispersive x-ray diffraction (ADXRD). A symmetric Diamond Anvil Cell was used in this study for pressures up to 16GPa and a Mao-Bell cell was used to achieve higher pressures up to 55GPa. Both of these experiments were conducted at the High Pressure Collaborative Access Team's (HP-CAT's) beamlines at the Advanced Photon Source: 16 BM-B and 16 ID-B. [Preview Abstract] |
Friday, October 29, 2010 4:36PM - 4:48PM |
D1.00004: Oxygen vacancies in lanthanum aluminate (LaAlO$_3$) Joshua Sayre, Nicola Spaldin Oxygen vacancies can affect the properties of an oxide in various manners such as increasing its ion or electronic conductivity, changing its lattice constant or causing dielectric breakdown. The aim of this research is to investigate structural changes and consequent changes in properties caused by oxygen vacancies in the model complex oxide, lanthanum aluminate, LaAlO$_3$. We use density functional theory within the local density approximation (LDA) and using the VASP package to calculate the structure and properties of representative oxygen vacancy profiles. We find that the presence of oxygen vacancies modifies the pattern of rotations of the oxygen octahedra. We discuss the implications of our results for understanding the correlation between epitaxial strain in oxide thin films and intrinsic defect profiles. [Preview Abstract] |
Friday, October 29, 2010 4:48PM - 5:00PM |
D1.00005: X-Ray Raman scattering of Aluminum Nitride under high pressure Neelanjan Bhattacharya, Michael Pravica We performed a high pressure study of aluminum nitride using x-ray Raman spectroscopy (XRS) up to 33 GPa in a diamond anvil cell at ambient temperature. We utilized the 16 ID-D undulator beamline at the Advanced Photon Source for the x-ray source. The spectrometer was set up to measure photons with about 410 eV energy loss (nitrogen edge) with respect to the elastic scattering energy (at 9.986 keV). The diamond cell was oriented relative to the x-ray beam so that the incident x-rays passed through a sample-confining beryllium gasket pressed between two diamonds. The inelastically scattered x-rays were collected by a fixed set of silicon mirrors. The Wurzite to rocksalt phase transition was observed upon pressure increase above 15 GPa, persisting in the rocksalt phase up to the highest pressure of this study. Upon pressure release to ambient pressure, a large hysteresis was observed. The sample has also been analyzed using micro-Raman and x-ray diffraction, which suggests pressure-induced amorphisation and the presence of mixed rocksalt and Wurzite phases. [Preview Abstract] |
Friday, October 29, 2010 5:00PM - 5:12PM |
D1.00006: Current Driven Drift Wave Turbulence and Electron Thermal Transport in Tokamaks C.J. Lee, P.H. Diamond, M. Porkolab Though tokamak reactor plasmas, such as ITER, are expected to be in electron transport dominated regimes, electron thermal transport in tokamaks has not yet been fully understood. In particular, recent analyses [1, 2] have indicated that current understanding cannot explain results from modest density, $T_e>T_i$ plasmas in either Ohmic or ECH heating regimes. Interestingly, such plasmas exhibit very large toroidal current drift parameters $(v_d/c_s > 1)$, which have been correlated with degradation of confinement [3]. These observations suggest revisitation of the electron velocity drift as an instability drive and trigger for heat transport through the electron channel. In this work, we examine the linear and nonlinear theory of current driven drift wave turbulence in tokamaks. Special attention is focused on the eigenfunction structure and spectral centroid shift induced by finite current. Note that the spatial asymmetry is a signature of current drive and has implications for flow generation and intrinsic rotation as well. We further explore nonlinear saturation mechanisms. Attention is focused to the effects of magnetic shear-induced resonance broadening of the electron response. \\ \noindent [1] L. Lin, M. Porkolab et al., PPCF, 2009. \newline [2] J.C. DeBoo et al., Phys. Plasmas, 2010. \newline [3] L. Lin, APS-DPP invited talk, 2009. [Preview Abstract] |
Friday, October 29, 2010 5:12PM - 5:24PM |
D1.00007: X-ray Thomson scattering from proton heated Boron Nitride Paul Davis, S. LePape, P. Neumayer, A.L. Kritcher, T. Doeppner, A. Bennuzzi-Mounaix, A. Ravasio, C. Brown, D. Hochhaus, C. Fortmann, G. Gregori, O.L. Landen, S.H. Glenzer We present the first measurements of proton heated Boron Nitride using x-ray Thomson scattering. The experiment was performed on the 300J, 10 ps Titan laser at Lawrence Livermore National Laboratory. The ultra-intense laser beam was split into two beams: 30$\%$ of the energy was directed onto a 10 $\mu$m Aluminum foil to generate a proton beam, and the remaining 70$\%$ was focused onto a 10 $\mu$m iron foil to generate a K-$\alpha$ backlighter at 6.4 keV. The proton beam isochorically heated a Boron Nitride foil, creating a solid density plasma with a temperature between 10-20 eV. X-rays were forward-scattered from the heated target onto a curved HOPG crystal, providing an accurate measurement of the temperature from the ratio of up- vs. down-shifted plasmon signals. *This work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory, through the Institute for Laser Science and Applications, under contract DE-AC52-07NA27344. The authors also acknowledge support from Laboratory Directed Research and Development Grant No. 08-LW- 004. [Preview Abstract] |
Friday, October 29, 2010 5:24PM - 5:36PM |
D1.00008: X-rays and Magnetism -- A Perfect Match Hendrik Ohldag Today's fundamental and applied magnetism research is particularly focused on magnetic materials that are suitable as magnetic sensors, spin valves, spin transistors or magnetic media consisting of complex magnetic multilayer structures. Scientific investigations in this area are concerned with the origin of magnetic coupling, spin transport across interfaces, magnetic properties of magnetic oxides and the complex magnetic structures which evolve when different kind of magnets for example antiferromagnets (AF) and ferromagnets (FM) are brought into contact. Dichroism x-ray absorption spectroscopy (XAS) using sycnhtron radiation represents a unique tool to understand complex nanomagnetic samples. The power of XAS is that it provides a possibility to address individual magnetic properties of different elements in a sample and a way to distinguish between different magnetic order like AF and FM order at the same time. It can furthermore be used to study the magnetism of buried interfaces, diluted magnetic systems like FM semiconductors or other exotic new magnets. The pulsed nature of the synchrotron as x-ray source allows for studying the time dependent behavior of a sample with a temporal resolution of a few tens of picoseconds. Dichroism soft x-ray absorption spectroscopy can furthermore be used to obtain spatially resolved information with less than 50nm lateral resolution in a modern full field or scanning x-ray microscopes. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700