Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session P40: Semiconductors: Structure, Surface, and Phase Transitions |
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Sponsoring Units: FIAP Chair: Roy Clarke, Univeristy of Michigan Room: Colorado Convention Center 503 |
Wednesday, March 7, 2007 11:15AM - 11:27AM |
P40.00001: Interfacial Structure, Bonding and Composition of InAs and GaSb Thin Films Determined Using COBRA Codrin Cionca, Donald Alan Walko, Yizhak Yacoby, Catalina Dorin, Joanna Mirecki Millunchick, Roy Clarke We have used Bragg rod x-ray diffraction and Coherent Bragg Rod Analysis (COBRA) direct phase retrieval method to extract atomic resolution electron density maps of a complementary series of heteroepitaxial III-V semiconductor samples. From the 3D electron density maps we derived the spacing between monolayers, the chemical composition and the distribution of bond lengths for all atomic planes in the film and across the interface with the substrate. InAs films grown on GaSb (001) using different As species (dimer or tetramer form) both showed conformal roughness and mixed GaSb/InSb interfacial bonding character. The tetramer conditions favored InSb bonding at the heterointerface; the percentages corresponding to InSb and GaAs bonding were equal in the case of the dimer. The GaAs film grown on InAs (001) displayed significant In and As interdiffusion and had a significant percentage of GaAs-like bonds at the heterointerface. [Preview Abstract] |
Wednesday, March 7, 2007 11:27AM - 11:39AM |
P40.00002: A RHEED study on the self-assembly of InAs quantum dots on GaAs(001) by MBE Itaru Kamiya, Kohtaro Matsuura, Tsuyoshi Higashinakagawa Control of size, density, and distribution of self-assembled (SA) quantum dots (QDs) by epitaxial growth remains to be a challenge. Reflection high-energy electron diffraction (RHEED) observation on nucleation and formation of SA InAs QD growth on GaAs(001) by MBE has been performed to shed light on this issue. RHEED specular beam, which provides us with information about the formation of QDs through rise of chevron-shape patterns, are measured \textit{in situ}. The results obtained under low InAs growth reveal that there are processes dependent and independent of growth rate. In addition, the results indicate that surface migration of In/As atoms and their incorporation into QDs, with the aid of the wetting layer, can be observed. Such information is complementary to the previously obtained results by STM or AFM, and provides us with the opportunity to understand the dynamics during QD formation. Based on these results, we propose a model on the QD formation process. [Preview Abstract] |
Wednesday, March 7, 2007 11:39AM - 11:51AM |
P40.00003: Molecular Dynamics Simulations of the Nanoparticle-Substrate Collisions Traian Dumitrica, Paolo Valentini Nanoparticle impact allows for the production of high quality thin films. To elucidate the microscopic details of nanoparticle-surface collisions in the low energy range (up to 1 eV/atom) of interest for the hypersonic plasma deposition technology, we have performed molecular dynamics simulations employing incident silicon particles of different sizes that are focused onto a silicon substrate. Our simulations offer a detailed microscopic picture of the dynamics of the collision process, including the energy conversion and redistribution, the local heating and melting, and the nanoparticle-surface bonding. Interestingly, beyond an impacting velocity threshold our simulations identified a soft landing regime mediated by a structural phase transition occurring in the nanoparticle. More insight into the pressure-induced structural phase transition was obtained by separate nanomechanical studies for the response of silicon nanoparticles to compression. [Preview Abstract] |
Wednesday, March 7, 2007 11:51AM - 12:03PM |
P40.00004: Measuring and Modeling Dopant Charging in Semiconductors using a Scanning Probe Method Stuart Tessmer, Irma Kuljanishvili, Cemil Kayis, James Harrison, Carlo Piermarocchi, Thomas Kaplan, Loren Pfeiffer, Ken West The ability to manipulate and probe small numbers of dopant atoms in semiconductors represents an emerging line of research, motivated by the continued miniaturization of semiconductor devices and potential applications where the dopants themselves form the functional part of a device. For example, the low-lying electronic states of donor atoms have been proposed as candidate systems for quantum computation. We have performed a localized measurement of the electron addition spectrum of silicon donors in a gallium-arsenide heterostructure using a scanning probe technique. The data are compared to a theoretical model based on the idea that nearest-neighbor pairs effectively form two-donor-molecules. To the best of our knowledge, this is the first low-temperature scanning probe measurement to resolve individual electrons entering a semiconductor system. [Preview Abstract] |
Wednesday, March 7, 2007 12:03PM - 12:15PM |
P40.00005: Self-Consistent Non-Equilibrium Green's Function Considerations in STM Height Models Applied to Si(100) K.H. Bevan, F. Zahid, D. Kienle, H. Guo In this study we report on the self-consistent non-equilibrium potential drop between Si(100) and a scanning tunneling microscope (STM) tip. It is found to play a role in the height characteristics of adsorbed hydrocarbons in conjunction with the silicon band gap. Results are reported for styrene against a hydrogen passivated Si(100) background. The potential drop is found to reduce the effective STM height of styrene by shifting molecular levels. Calculations are performed within density functional theory (DFT) under both the self-consistent and non-self consistent non-equilibrium Green's function (NEGF) formalism. Tunneling current distance dependence is captured by an ab-initio basis via free pseudo-potential eigenstates benchmarked for clean metallic surfaces. The resulting trends indicate that participation of an applied bias potential profile in measured STM surface heights should not be limited to Si(100). [Preview Abstract] |
Wednesday, March 7, 2007 12:15PM - 12:27PM |
P40.00006: ABSTRACT WITHDRAWN |
Wednesday, March 7, 2007 12:27PM - 12:39PM |
P40.00007: Low energy positrons as probes of reconstructed semiconductor surfaces. Nail G. Fazleev, Alex H. Weiss Positron probes of semiconductor surfaces that play a fundamental role in modern science and technology are capable to non-destructively provide information that is both unique to the probe and complimentary to that extracted using other more standard techniques. We discuss recent progress in studies of the reconstructed Si(100), Si(111), Ge(100), and Ge(111) surfaces, clean and exposed to hydrogen and oxygen, using a surface characterization technique, Positron-Annihilation-Induced Auger-Electron Spectroscopy (PAES). Experimental PAES results are analyzed by performing first-principles calculations of positron surface states and annihilation probabilities of surface-trapped positrons with relevant core electrons for the reconstructed surfaces, taking into account discrete lattice effects, the electronic reorganization due to bonding, and charge redistribution effects at the surface. Effects of the hydrogen and oxygen adsorption on semiconductor surfaces on localization of positron surface state wave functions and annihilation characteristics are also analyzed. Theoretical calculations confirm that PAES intensities, which are proportional to annihilation probabilities of the surface trapped positrons that results in a core hole, are sensitive to the crystal face, surface structure and elemental content of the semiconductors. [Preview Abstract] |
Wednesday, March 7, 2007 12:39PM - 12:51PM |
P40.00008: The type-C defect on the Si(001)-2$\times$1 surface Ja-Yong Koo, Sang-Yong Yu, Hanchul Kim The type-C defect is the last unresolved point defect on the Si(001)-2$\times$1 surface. Several kinds of atomic models have been suggested as the origin of the C-defect. We investigated the clean Si(001)-2$\times$1 surface by scanning tunneling microscopy to measure the statistical distribution of several kinds of point defects on the surface. We compared the results on the clean surface with the adsorption of water molecules on the Si(001)-2$\times$1 surface. We discuss the possibility of water molecules as the origin of the type-C defect on Si(001)-2$\times$1. [Preview Abstract] |
Wednesday, March 7, 2007 12:51PM - 1:03PM |
P40.00009: Self-Alignment of Dimer Vacancies on Si(001) Arief Budiman A formation of single dimer vacancy line on a reconstructed Si(001) terrace can be understood from their interaction elastic energy and configuration entropy. Both reconstructed terrace and dimer vacancies are represented by elastic dipoles. A grand canonical ensemble is used to analyze four possible alignments of a dimer vacancy line on such terrace. The self-organization is induced by an elastic interaction between the dimer vacancy and the reconstructed terrace and a kinematic restriction for a line to have a maximum length equal to terrace width when aligned perpendicular to the step direction. Numerical simulations using the obtained energy expression also reveal the importance of elastic interaction in inducing motion of dimer vacancies, while their self-alignment to forming a line is assisted by chemical bond between nearby dimer vacancies. [Preview Abstract] |
Wednesday, March 7, 2007 1:03PM - 1:15PM |
P40.00010: $\alpha -$ to $\beta $- to $\gamma $-spinel transformations in Mg$_{2}$SiO$_{4}$. Zhongqing Wu, Yonggang Yu, Renata Wentzcovitch Phase relations in Mg$_{2}$SiO$_{4}$ have been investigated by first principles quasiharmonic calculations. The $\alpha $- to $\beta $-spinel transition is believed to cause the 410-km discontinuity, while the $\beta $- to $\gamma $-spinel transformation may contribute to the 520-km discontinuity. We have obtained these phase boundaries using LDA and PBE/GGA exchange correlation functionals and results confirm the trend usually displayed by these functionals. Information on this series of transformations in Mg$_{2}$SiO$_{4}$ will help us understand the importance of other elements on this sequence of phase transformations across the Earth's transition zone. [Preview Abstract] |
Wednesday, March 7, 2007 1:15PM - 1:27PM |
P40.00011: DFT study of the structural properties of silver halides: LDA vs GGA calculations. G. Murrieta, R. de Coss, L.A. Palomino-Rojas, M. Lopez-Fuentes, G.H. Cocoletzi, N. Takeuchi We perform total energy calculations to investigate the atomic structure of three silver halides: AgCl, AgBr, and AgI in the sodium chloride, cesium chloride, zincblende and wurtzite structures. Calculations are done within the density functional theory. We employ the full potential LAPW method, and the exchange-correlation potential energies are treated in the LDA and GGA approximations. We find that LDA correctly predict the ground state structure of all three binary compounds: rocksalt for AgCl and AgBr, and zincblende/wurtzite for AgI, while GGA always prefer the more covalent zincblende/wurtzite configurations. We observe that the distribution of electron densities for rocksalt is more homogeneous than for zincblende. As a consequence, the energy difference between zincblende/wurtzite and rock-salt phases is enhanced in the GGA approximation, predicting the wrong ground state structure for AgCl and AgBr. Assuming the right experimental structure, the GGA approximation gives lattice parameters, bulk moduli and cohesive energies closer to experimental values. [Preview Abstract] |
Wednesday, March 7, 2007 1:27PM - 1:39PM |
P40.00012: The high-pressure structural phase transition in~heavier RH3 (R: rare earth metals) by ab initio theory Wei Luo, Rajeev Ahuja Rare earth hydrides are very interesting because they exhibit a reversible metal-insulator transition upon hydrogenation. In present work, we have studied the structural stabilities of heaver~rare earth~trihydrides, RH3 (R=Sm, ..., Lu), under high pressure~using ab initio calculations. Our results show the hexagonal structure with HoD3-type structure is stable~for all studied RH3 at ambient pressure.~Further~these RH3~transform to a face-center cubic structure under high pressure. In HoD3-type phase bulk modulus decreases, whereas the~transition pressure for~hexagonal to fcc structural transformation increases,~as the atomic number of rare earth~element increases. [Preview Abstract] |
Wednesday, March 7, 2007 1:39PM - 1:51PM |
P40.00013: Phase transition of the Ge-Sb-Te(GST) ternary alloy system for the phase-change memory Jae-Hyeon Eom, Jino Im, Jin-Woo Jung, Young-Gui Yoon, Ki-Min Park, Jisoon Ihm A theoretical investigation on the phase transition from the crystalline to the amorphous phase of the Ge-Sb-Te(GST) ternary alloy system for the phase-change memory is presented. The local structure of the amorphous phase of the GST is shown to be composed of the stibnite-like structure for the Sb$_2 $Te$_3$ and chain-like structure for the GeTe by examining the coordination number for (GeTe)$_n$(Sb$_2$Te$_3$)$_m$ homologous series. The phase transition occurs by the change of the arrangement and connection between the building blocks while the structure of the building blocks is preserved. Energy barriers, transition states and the change of the electronic states during the phase transition are obtained using ab initio electronic structure calculations. [Preview Abstract] |
Wednesday, March 7, 2007 1:51PM - 2:03PM |
P40.00014: Structural phase transition of GeTe under pressure Gap-Sok Do, Seung-Hoon Jhi Structural phase transition of a representative chalcogenide semiconductor, GeTe, is studied with the use of ab initio pseudopotential density functional method. The transition pressure and atomic structures are particularly investigated. By fitting calculated energy-volume data with Birch-Murnaghan equation, we obtained a transition pressure of 3.7 GPa for rhombohedral to NaCl structural transition and 42 GPa for NaCl to CsCl transition, which is in an excellent agreement with experiment [1, 2]. Other structures are also studied for possible transitions at intermediate pressures. The role of Te d orbitals is discussed in regard to the transition pressure and cohesive energy. \newline \newline [1] Onodera A, Sakamoto I, Fujii Y, Mori N and Sugai S, Phys. Rev. B 56 , 7935(1997) \newline [2] N. R. Serebryanaya, V. D. Blank, V. A. Ivdenko, Phys. Lett. A 197, 63 (1995) [Preview Abstract] |
Wednesday, March 7, 2007 2:03PM - 2:15PM |
P40.00015: Development of a neural network based algorithm for multi-scale roughness~parameters of In6S7 semiconductucting compound. Raouf Bennaceur, Lilia Bennaceur Farah, Imed Riadh Farah, Houda Ben Abdallah The overall objective of this paper is to retrieve In6S7 semiconducting roughness surfaces parameters by inverting the backscattered EM waves. Because the classical description of roughness using statistical parameters like the correlation length doesn't lead to satisfactory results to predict backscattering, we used a multi-scale roughness description using the wavelet transform and the Mallat algorithm. In this description, the surface is considered as a superposition of a finite number of one-dimensional Gaussian processes each having a spatial scale. A second step in this study consisted in adapting a direct model simulating backscattering namely the small perturbation model to this multi-scale surface description. We investigated the impact of this description on backscattering through a sensitivity analysis of backscattering coefficient to the multi-scale roughness parameters. The dielectric constants are obtained from ab initio FPLAPW band structure calculation. To perform the inversion of the small perturbation multi-scale scattering model (MLS SPM) we used a multi-layer neural network architecture trained by back propagation learning rule. The inversion leads to satisfactory results with a relative uncertainty of 8 {\%}. [Preview Abstract] |
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