Bulletin of the American Physical Society
2005 72nd Annual Meeting of the Southeastern Section of the APS
Thursday–Saturday, November 10–12, 2005; Gainesville, FL
Session GB: Condensed Matter V: Materials Physics: Modeling |
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Chair: Kevin Ingersent, University of Florida Room: Hilton Hawthorne |
Friday, November 11, 2005 10:45AM - 10:57AM |
GB.00001: Multiscale Modeling of Fracture in an SiO$_{2}$ Nanorod Aditi Mallik, Keith Runge, Krishna Muralidharan, James Dufty The fracture of a 108 particle SiO$_{2}$ nanorod under uniaxial strain is described using an NDDO quantum mechanics. The stress -- strain curve to failure is calculated as a function of strain rate to show a domain that is independent of strain rate. A pair potential for use in classical MD is constructed such that the elastic portion of the quantum curve is reproduced. However, it is shown that the classical analysis does not describe accurately the large strain behavior and failure. Finally, a composite rod is constructed with a small subsystem described by quantum mechanics and the remainder described by classical MD $^{1}$. The stress -- strain curves for the classical, quantum, and composite rods are compared and contrasted. 1. ``Multiscale Modeling of Materials -- Concepts and Illustration'', A. Mallik, K. Runge, J. Dufty, and H-P Cheng, cond-mat 0507558. [Preview Abstract] |
Friday, November 11, 2005 10:57AM - 11:09AM |
GB.00002: Lennnard Jones Potential for Mesoscopic System Jutri Taruna, Bradley Futch, Jorge Piekarewicz The liquid-gas phase transition of a Lennard Jones system of $N=500$ particles is studied via Molecular Dynamics simulations. Rather than displaying a positive isothermal compressibility --- as is demanded of stable systems in the thermodynamic limit --- the system develops a ``Van der Waals loop'', namely, a region with negative isothermal compressibility. We use various observables as well as state-of-the-art computer renderings to elucidate the nature of this behavior. [Preview Abstract] |
Friday, November 11, 2005 11:09AM - 11:21AM |
GB.00003: An Analytic Study of Energy Eigenstates of Piecewise-constant Potentials Using the Wigner Quasi-probability Distribution Mario Belloni, Laura Gilbert, Michael Doncheski, Richard Robinett In the study of classical oscillating systems, a phase-space description is often useful in determining the long-term properties of a system’s motion. Wigner, over 70 years ago, was one of the first to introduce a phase-space description of quantum mechanics with a quasi-probability density joint in $x$ and $p$. The Wigner function is considered a ``quasi"- probability density because it can be negative for states which lack a classical analog and because of obvious problems raised by the Heisenberg uncertainty principle which restrict the ability to make simultaneous measurements of both $x$ and $p$. While many standard potentials have been analyzed using the Wigner function, including that of the free and accelerating particle and the harmonic oscillator, other familiar bound-state problems have not. We calculate the Wigner quasi-probability distribution for the energy eigenstates of several standard piecewise-constant one-dimensional potentials---attractive Dirac delta function, infinite well, finite well, asymmetric infinite well---as well as visualize the results. [Preview Abstract] |
Friday, November 11, 2005 11:21AM - 11:33AM |
GB.00004: Accuracy of Boltzmann Full-impurity-ionization Approximation on Surface Recombination DC Current-Voltage Characteristics. Zuhui Chen, Bin B. Jie, Chih-Tang Sah Surface recombination DC Current-Voltage (RDCIV) characteristics are used to extract interface properties of Metal-Oxide-Semiconductor (MOS) structure, such as interface trap density and surface dopant impurity concentration. The steady-state Shockley-Read-Hall kinetics with Boltzmann distribution and full-impurity-ionization (BI) approximation are used. Compared with the Fermi distribution and impurity-deionization (FD) theory, the BI approximation gives orders of magnitude higher computation speed required in computer aided integrated circuit design. Accuracy of BI approximation is analyzed by computing the derivation from the exact FD theory, with wide ranges of MOS parameters (substrate dopant impurity concentration, gate oxide thickness, forward source/drain junction bias, interface trap energy level, and transistor temperature). It is shown that BI approximation deviates from the exact FD theory by less than 5{\%} over the practical range of these five parameters. [Preview Abstract] |
Friday, November 11, 2005 11:33AM - 11:45AM |
GB.00005: Effect of Temperature on Surface Recombination Current at SiO$_{2}$/Si Interface Traps Bin B. Jie, Zuhui Chen, Chih-Tang Sah Temperature dependences of recombination current at interface traps in MOS transistor structure are investigated using the Shockley-Read-Hall DC recombination-current-voltage (R-DCIV) characteristics. Results include the effects of energy distribution of the interface traps (discrete, constant and U-shaped energy distributions) on the temperature dependences of the base-terminal-current-versus-gate-voltage lineshape (I$_{B}$-V$_{GB})$, peak current and voltage (I$_{B-peak,}$ V$_{GB-peak})$ and their thermal activation energy E$_{A}$, and the reciprocal slope n of the I$_{B-peak}$ versus base/drain (or base/source) p/n junction forward voltage V$_{BD}$. Surface impurity concentration and oxide thickness are varied. Temperature dependences of E$_{A}$, V$_{GB-peak}$ and n are small while I$_{B-peak}$ and R-DCIV linewidth, large. The insensitivity of I$_{B-peak}$ and n on material properties allows experimental extraction of effective interface trap energy distribution. [Preview Abstract] |
Friday, November 11, 2005 11:45AM - 11:57AM |
GB.00006: Effects of Energy Distribution of Interface Traps on Recombination DC Current-Voltage Lineshape Chih-Tang Sah, Zuhui Chen, Bin B. Jie Effects of energy distributions of interface traps in silicon energy gap on recombination DC current-voltage (R-DCIV) characteristics or lineshape are analyzed using Shockley-Read-Hall kinetics. The lineshape is mainly determined by interface traps around silicon midgap, not much affected by the ratio of electron and hole capture rates. On p-type silicon or the p-basewell of inversion n-channel MOS transistor, interface traps above the midgap broaden the lineshape in the accumulation gate-voltage (negative) range, while those below the midgap, the inversion (positive) gate-voltage range. Slater's theory anticipates U-shaped energy distribution of interface traps, which is assumed in this R-DCIV evaluation, showing that the broadened lineshape observed in past experiments, previously attributed to spatial variation of surface dopant impurity concentration, can also arise from energy distribution of interface traps. [Preview Abstract] |
Friday, November 11, 2005 11:57AM - 12:09PM |
GB.00007: A Dynamic Charge Potential for Water Krishna Muralidharan, Susan Atlas, Steve Valone, Keith Runge We present a new \textit{ab initio} based interatomic potential for water clusters and liquid water capable of accounting for electronic induction through hydrogen bonding and non-bonding interactions. Though the functional form of the potential is similar to embedded atom method (EAM) formulations, an important difference lies in the fact that the atomic electron densities are environment dependent. This study modifies EAM methods to describe systems, like water, where the role of induction is vital. [Preview Abstract] |
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