Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Y20: Glassy and Amorphous Materials |
Hide Abstracts |
Sponsoring Units: DMP DCMP Chair: Frances Hellman, University of California, Berkeley Room: C120-122 |
Friday, March 19, 2010 8:00AM - 8:12AM |
Y20.00001: Structure and dynamics of iron doped and undoped silicate glasses Cristiane N. Santos, Domingos D.S. Meneses, Patrick Echegut, Emmanuel Lecomte The optical properties of common silicate glass compositions are well known at room temperature. However, their radiative properties and structural evolution of these glasses with temperature are still largely unexplored. In this work we have measured the emissivity of a set of iron doped and undoped silicate and borosilicate glasses over an unprecedented temperature (up to 1700 K) and spectral range (40 -- 20000 cm$^{-1})$. This was achieved by means of a home-made apparatus composed of a CO$_{2}$ laser as the heat source, a black-body reference and two spectrometers. The optical functions were assessed using a dielectric function model [1], and the structure and dynamics of the glassy network, as well the absorption of iron species in different redox states were evidenced. We believe that these new data will help to understand the heat transfer in molten silicates. \\[4pt] [1] D. D. S. Meneses, G. Gruener, M. Malki, and P. Echegut, J. Non-Cryst. Solids \textbf{351}, 124 (2005) [Preview Abstract] |
Friday, March 19, 2010 8:12AM - 8:24AM |
Y20.00002: Optical and structural characterization of yttrium calcium borate glasses Cristiane Santos, Domingos D.S. Meneses, Patrick Echegut, Daniel R. Neuville, Antonio C. Hernandes, Alain Ibanez Structural and optical properties of new stable glasses in the Y$_{2}$O$_{3}$ -- CaO -- B$_{2}$O$_{3}$ system, containing the same Y/Ca ratio as the YCa$_{4}$O(BO$_{3})_{3}$ (YCOB) crystal, were determined from Raman and reflectance infrared spectroscopy [1]. We have obtained the optical functions using a dielectric function model and their evolution with composition are associated with an increase in the number of non-bridging oxygen and to calcium/yttrium oxides content with the formation of pentaborate, metaborate, orthoborate and pyroborate groups. The orthoborate and pyroborate signatures increase with increasing the modifier cations. Refractive indexes values (from 1.597 to 1.627 at $\lambda $ = 2 $\mu $m) are in good agreement with those of the YCOB crystal, an indication that these glasses are potential candidates for doping with rare-earth ions for optical applications. \\[4pt] [1] C. N. Santos, D.D.S. Meneses, P. Echegut, D. R. Neuville, A. C. Hernandes, A. Ibanez, Appl. Phys. Lett. \textbf{94}, 151901(2009). [Preview Abstract] |
Friday, March 19, 2010 8:24AM - 8:36AM |
Y20.00003: Light-Induced Electron Paramagnetic Resonance Studies of the Phase Change Material a-Ge$_{2}$Sb$_{2}$Te$_{5}$ David Baker, P. Craig Taylor, Tining Su, Brian Simonds, Youn Gu Understanding the microscopic mechanisms for the reversible phase changes in chalcogenide phase-change memories is one of the most important tasks in improving the performance of these devices. ~In particular, understanding whether the defects in the amorphous phase possess a strong electron-lattice interaction is critical. ~ Studies of as-deposited amorphous Ge$_{2}$Sb$_{2}$Te$_{5}$ (GST) by light-induced electron paramagnetic resonance (LESR) are presented. RF sputtered GST films were grown to thicknesses of roughly 1.0 micrometer. The sample was then powdered to maximize the volume as detected by the ESR spectrometer. \textit{In-situ} measurements of the GST sample by ESR while exposing the sample with bandgap light to induce paramagnetic defects, and subsequent exposure to sub-bandgap light to bleach these defects were performed. Bleaching experiments as a function of excitation energy suggest the presence of so-called ``negative U'' centers, which must be considered in any models of the phase change process. [Preview Abstract] |
Friday, March 19, 2010 8:36AM - 8:48AM |
Y20.00004: Electrical transport mechanism studies of amorphous Ge2Sb2Te5 films at nm scales Wenjian Lu, Chanjong Ju, Kookrin Char We fabricated the amorphous Ge$_2$Sb$_2$Te$_5$ (GST) films with different thicknesses ranging 10-100 nm by dc magnetron sputtering in trilayer geometry using metal top and bottom electrodes. Temperature and voltage bias dependent measurements of the electrical conductance have been employed to study the transport mechanism of the amorphous GST films at different length scale. At low temperatures, the electrical transport is dominated by the inelastic hopping through directed chains of localized states. With increasing temperature and length the variable range hopping (VRH) conductivity is induced, which is associated with the diffusive regime. At high temperatures, a thermally activated process is observed. The estimated values for the activation energy $E_\alpha$ and the carrier density $n$ are 0.42 eV and 10$^{18}$ cm$^{-3}$, respectively. When compared with the typical amorphous silicon, the amorphous GST seems to exhibit much larger localization length, which results in the difficulty of reaching the bulk limit even for the 100 nm thick GST film. [Preview Abstract] |
Friday, March 19, 2010 8:48AM - 9:00AM |
Y20.00005: Structural evolution of Mg and Mg-rich bulk alloy during thermal expansion and rapid quenching by ab initio molecular dynamics Masae Takahashi Magnesium alloy are becoming more and more attractive for lightweight structural application. Recently, the Mg bulk alloy containing a very small amount of Zn and Y with excellent mechanical properties was developed. To reveal the wonderful effect of the very small amount of additives and furthermore evidence our recent prediction of anisotropic elongation in c-axis in the inflation process of Mg-clusters under charge transfer in bulk alloy, we investigated here structural transitions of Mg and Mg-rich alloy during thermal expansion and quenching processes by ab initio molecular dynamics simulation. The variations with temperature of linear thermal expansion coefficients, total energies, and radial distribution functions have been characterized. Anisotropic thermal expansion of Mg metal and the discrete jump of thermal expansion coefficients around 700 K was found. During the expansion processes, simple thermal vibrations, large atomic displacements in ab plane, and additional displacements in the direction of c axis were observed. The results qualitatively agreed with experimental observation. [Preview Abstract] |
Friday, March 19, 2010 9:00AM - 9:12AM |
Y20.00006: Glass transition in structural-glass models Ruben S. Andrist, Derek Larson, Helmut G. Katzgraber The 10-state Potts glass in mean-field is commonly used to study structural glasses because the equations describing the dynamics near the transition are mathematically similar to those for structural glasses. Simulations in three space dimensions show no sign of a transition into a stable glass phase. It is, however, unclear if a transition exists for high space dimensions below the upper critical dimension. We study the critical behavior of the 10-state Potts glass on a one-dimensional topology with power-law modulated interactions. The model has the advantage over conventional short-range systems in that large sizes can be simulated for high effective space dimensions. Furthermore, by changing the power of the interactions we can tune the system from the mean-field to the short-range universality class. Using parallel tempering Monte Carlo we probe the existence of a finite-temperature phase transition by studying the spin-glass susceptibility and the two-point finite-size correlation length. Preliminary results suggest that a stable glass phase might exist for finite space dimensions below the upper critical dimension. [Preview Abstract] |
Friday, March 19, 2010 9:12AM - 9:24AM |
Y20.00007: The effect of hydrogen on the radiation-enhanced viscosity of amorphous silicon. Jean-Francois Joly, Sjoerd Roorda, Normand Mousseau, Laurent Lewis It has long been known that ion bombardment reduces the viscosity of disordered solids by many orders of magnitude. The exact explanation for this phenomenon has not yet been found but defect generation and defect mobility under ion bombardment is expected to have an important effect on the physical properties of materials. Since hydrogen increases the stability of disordered networks by bonding to dangling bonds, its presence should therefore lead to an increase of the radiation-enhanced viscosity of a-Si by reducing the mobility of defects. A characterization of the effect of H on the mobility of these defects could therefore enable a deeper understanding of the nature of defects in amorphous silicon. In this work, we investigate the role of H at concentrations up to 3.5 at. {\%}, injected in amorphous silicon layers 1,4 um thick made by 1 MeV self-ion implantation. The samples were initially set in different states of stress and annealed at 475 C, then bombarded by 1 MeV Si+ ions to induce viscous flow. The subsequent stress reduction was measured from in-situ curvature measurements. Results indicate that the viscosity increases with hydrogen content. This suggests that defects containing dangling bonds, like vacancies, are responsible in part in enabling large scale mass transport in amorphous silicon. [Preview Abstract] |
Friday, March 19, 2010 9:24AM - 9:36AM |
Y20.00008: First-principles simulations of Raman spectra of As-S glasses Chamila Dharmawardhana, Koblar Jackson First principles cluster calculations were used to interpret the experimental Raman spectra of As$_{x}$S$_{(1-x)}$ glasses. A large array of cluster models was built to mimic various atomic arrangements and a range of stoichiometries. The dangling bonds on the models were terminated by hydrogen atoms. Using density functional theory, cluster geometries were optimized and vibrational modes and their corresponding Raman/IR activity calculated. P$_{x}$S$_{(1-x)}$ models were also studied for comparison. From the cluster energetics, a clear preference for heteropolar bonds was confirmed for both systems. The results of the Raman calculations accounted well for the width of the peaks in the observed spectra and the identities of the main vibrational bands were confirmed. Strong evidence was found for the presence of so called Quasi-Tetrahedral (QT) units as proposed recently by the Boolchand group. The study shows the applicability and predictive capabilities of using cluster calculations in analyzing bulk glasses. [Preview Abstract] |
Friday, March 19, 2010 9:36AM - 9:48AM |
Y20.00009: Anomalous Crystal Growth In Supercooled OTP On Temperature Cycling Stephen C. Hall, Sean Lindsay It has been previously observed [1] that when the fragile glass former o-terphenyl (OTP) is supercooled to -23 $^{\circ}$C, well below its normal freezing temperature but above its glass transition temperature, an anomalous growth mode appears indicated by a sudden increase in the crystal growth velocity. We report observations of this anomalous crystal growth when the temperature is raised briefly above the apparent transition temperature and then cooled back down. We find that when the temperature is raised to -20.5 $^{\circ}$C or less the original anomalous growth continues to grow, apparently uninterrupted. When the temperature is raised above -19 $^{\circ}$C the original anomalous growth does not continue to grow, although new anomalous growth nucleates. One interpretation of these results is that the transition temperature for the anomalous growth is around -20 $^{\circ}$C. \\[4pt] [1] M. Hatase, M. Hanaya, and M. Oguni, J. Non-Cryst. Solids \underline{333}, 129 (2004) [Preview Abstract] |
Friday, March 19, 2010 9:48AM - 10:00AM |
Y20.00010: Reciprocal-Space Approach for Atomic Interactions and Configuration Correlations in Highly Inhomogeneous Systems Volodymyr Bugaev, Alexander Udyansky, Peter Wochner We have developed a statistical-thermodynamic k-space approach [1], which enables us to unveil local symmetries and mid-range order in highly inhomogeneous, e.g., amorphous metallic and colloidal systems. On the basis of coherent scattering data we extract parameters of interaction potentials, which then are used in calculations of the pair-wise and specifically constructed many-body correlation functions. In particular, the orientational pair-pair correlations describe the structure of mid-range clusters [2]. We will present results of our calculations for model and actual colloidal systems. \\[4pt] [1] V.N. Bugaev, A. Udyansky, O. Shchyglo, H.Reichert, and H. Dosch, Phys. Rev. B 74, 024202 (2006)\\[0pt] [2] P. Wochner, C. Gutt, T. Autenrieth, T. Demmer, V. Bugaev, A.D. Ortiz, A. Duri, F. Zontone, G. Gr\"{u}bel, and H. Dosch, PNAS 106, 11511-11514 (2009). [Preview Abstract] |
Friday, March 19, 2010 10:00AM - 10:12AM |
Y20.00011: Excess low temperature heat capacity in a-Si:H thin films prepared by hot-wire CVD Daniel Queen, Frances Hellman, Richard Crandall, Qi Wang Thin films of $a$-Si:H prepared by hot-wire chemical vapor deposition (HWCVD) have previously been found to have orders magnitude lower density of two-level systems (TLS) as measured by internal friction. These TLS are thought to be responsible for the low temperature universality seen in thermodynamic measurements in all amorphous materials. We present heat capacity measurements using our MEMS nanocalorimeter on a range of $a$-Si and $a-$Si:H films prepared by e-beam evaporation and HWCVD. The tunneling model predicts that a reduction in the TLS should result in Debye-like heat capacity. However, we find that the low temperature heat capacity of $a$-Si:H prepared by HWCVD is two orders of magnitude larger than crystalline silicon at 2K. [Preview Abstract] |
Friday, March 19, 2010 10:12AM - 10:24AM |
Y20.00012: Molecular modeling of a stable glass -- the case of trehalose Sadanand Singh, Devin Averett, Juan de Pablo Recently, a new class of glasses --stable glasses- has been identified in experiments using physical vapor deposition of indometahcin (IMC) and 1,3,5-(tris)naphthylbenzene (TNB) [1,2]. These glasses have been shown to exhibit lower enthalpies (by as much as 10J/g), higher glass transition temperatures, higher onset temperature when subjected to plasticization and higher densities (by $\sim $2{\%}) than traditional, ordinary glasses. We propose a molecular simulation method to generate stable glasses of an atomistic model of trehalose. The results of simulations are in good agreement with experiment: simulated stable trehalose glasses have an enthalpy that is 9.3 J/g lower and a density that is 1.6{\%} than traditional, ordinary glasses. The plasticization of stable glasses formed by our method shows an increase of the onset temperature from 378K to 450K. Further analysis shows that these glasses have higher mechanical strength and higher Q6 crystal order parameter than ordinary glasses. The molecules farthest from the substrate layer are observed to be more mobile than those in the bulk; a mechanism for stable glass formation is proposed that relies on this enhanced surface mobility. [1] S. F. Swallenet al., Science. 2007, 315, 353-356, [2] K. L. Kearns et al., J Chem. Phys. 2007, 127. [Preview Abstract] |
Friday, March 19, 2010 10:24AM - 10:36AM |
Y20.00013: Dynamic Phase Transitions in Driven Kinetically Constrained Lattice Models Thomas Speck Kinetically constraint models (KCMs) have become an important tool to study and understand the origin of glassy dynamics. While possessing trivial thermodynamic properties, their dynamics slow down dramatically for low temperatures, showing dynamical heterogeneity as attributed to glass forming supercooled liquids. A dynamical first order ergodic-nonergodic phase transition is observed when biasing the dynamics of KCMs in trajectory space. In contrast to the previous equilibrium models, we consider various modified KCMs driven into a nonequilibrium steady state through non-conservative forces. We use the concept of entropy production along single trajectories to bias the dynamics, leading to dynamical first-order phase transitions similar to those found for the unmodified models. Finally, we discuss how the biased dynamics can be mapped onto physical unbiased dynamics with modified forces. [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