Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session U13: Devices & Applications II |
Hide Abstracts |
Sponsoring Units: FIAP Chair: Ajul Koukar, University of Southern California Room: LACC 402B |
Thursday, March 24, 2005 8:00AM - 8:12AM |
U13.00001: Measuring equipment for thermophysical properties of droplet electromagnetically-levitated under axial static magnetic field Fumitomo Onishi, Kosuke Nagashio, Yuko Inatomi, Kazuhiko Kuribayashi EML is used for measurement of thermophysical properties melt with high melting point and with high reactivity. Application of a strong static magnetic field is considered to be a promising method to damp convection and motion in electrically conductive fluid, because the Lorentz force is induced by the magnetic field. Therefore, a novel measuring equipment for thermophysical properties of an electrically conductive droplet has been developed to solve the problem mentioned above based on the principle. In order to observe behavior and shape of melt three-dimensionally and in realtime, high-speed camera and CCD camera were mounted at the top and side of a reaction chamber of EML, respectively. Surface temperature of the melt was monitored by pyrometer from the side. Result, vibrations of Si, Ti droplets levitated by the equipment was stabilized and the convection was seemed to be damped under the magnetic field, though the droplets rotated along the magnetic field as rigid bodies. Some obtained results for thermophysical properties of the droplets will be reported. [Preview Abstract] |
Thursday, March 24, 2005 8:12AM - 8:24AM |
U13.00002: Extraordinary Optoconductance in GaAs-In Hybrid Structures K.A. Wieland, Y. Wang, S.A. Solin Following the demonstration of extraordinary magnetoresistance (EMR) in semiconductor-metal hybrids\footnote{ S.A. Solin et al., Science {bf289}, 1530 (2000).} it has been realized that EMR is but one example of a general class of EXX phenomena that can be geometrically enhance by the judicious choice of sample geometry, lead placement and the location, size and shape of any inhomogeneities. The second EXX phenomenon to be demonstrated was extraordinary piezoconductance, EPC\footnote{A. C. H. Rowe et al., Appl. Phys. Lett. {bf83}, 1160 (2003).}. Here we report a third EXX phenomenon, extraordinary optoconductivity, EOC. The optoconductivity of a macroscopic 4-contact van der Pauw plate structure consisting of Si-doped GaAs $(n\sim 1 times 10^{18}$ cm$^{-3})$ with an In shunt was compared to that of a shuntless sample. The conductance of each sample was measured as a function of temperature and of the position and wavelength of a focused Ar ion laser beam (spatial resolution of $10 \mu m$). At room temperature the short carrier mean free path $(\lambda)$ resulted in a photovoltaic response that was diminished by the shunt. In contrast, at low temperature the longer $\lambda$ results in EOC that, at 15K, is more than 400$\%$ larger in the shunted sample relative to the the unshunted sample. [Preview Abstract] |
Thursday, March 24, 2005 8:24AM - 8:36AM |
U13.00003: On Power dissipation in information processing Roman Ostroumov, Kang L Wang We consider power dissipation during simple switching in the informationally irreversible architecture. First, we investigate two limit cases of sudden and infinitesimal slow switching and then we derive solution for the general problem of the arbitrary speed switching in the two level system. The energy dissipation during errorless switching has a minimum of \textit {kTln(2)} and increases linearly with a switching speed. Both charge-position and spin degrees of freedom behave similarly in this model with the only difference being the relaxation times. We show that for a relaxation time of 1ps, power dissipation due to the finite switching speed at the operational frequencies of around 35GHz will become comparable to the \textit{kTln(2)} and total power dissipation per switch will become \textit{$\sim $2kTln(2).} [Preview Abstract] |
Thursday, March 24, 2005 8:36AM - 8:48AM |
U13.00004: Radiation-Induced Interface Traps in Silicon Bipolar Transistors Harold P. Hjalmarson, Charles E. Hembree, Ronald L. Pease Experiments on bipolar transistors have shown that gain degradation increases as the dose rate is reduced for a given total dose of ionizing radiation. We suggest that this effect is caused by competing reactions involving hydrogen released from oxide sites by the ionizing radiation. At low dose rates, most of the hydrogen reacts with hydrogen-passivated Si dangling bonds at the semiconductor-oxide interface to create interface traps (Pb-centers), but at higher dose rates a larger fraction of the hydrogen is consumed in other reactions that depend on the dose-rate. This presentation will discuss continuum calculations of the the interface trap density as a function of radiation dose rate. These calculations will be compared with experimental data for dose-rate dependent irradiation of test structures. [Preview Abstract] |
Thursday, March 24, 2005 8:48AM - 9:00AM |
U13.00005: Electronic Properties of Energetic Particle-Irradiated In-rich InGaN Alloys S.X. Li, R.E. Jones, E.E. Haller, K.M. Yu, J. Wu, W. Walukiewicz, J.W. Ager III, W. Shan, Hai Lu, William J. Schaff, W. Kemp InGaN alloys, whose fundamental bandgaps span almost perfectly the solar spectrum, are potential materials for high-efficiency tandem solar cells. We have carried out a systematic study on the effect of irradiation on the electronic and optical properties of InGaN alloys over the entire composition range. Three different types of energetic particles (electrons, protons, and alpha particles) were used to produce displacement damage doses ($D_{d})$ spanning five orders of magnitude. The electron concentrations in InN and In-rich InGaN increase with $D_{d}$ and finally saturate after a sufficiently high dose of irradiation. The saturation of carrier density is attributed to the Fermi level pinning at the Fermi Stabilization Energy ($E_{FS})$, as predicted by the amphoteric native defect model. Electrochemical capacitance-voltage (ECV) measurements reveal a surface electron accumulation whose concentration is determined by pinning at E$_{FS}$. Modeling with a combination of various scattering mechanisms provides an excellent fit with the mobility measurements. [Preview Abstract] |
Thursday, March 24, 2005 9:00AM - 9:12AM |
U13.00006: Energy Loss and Stopping Cross Section Factors for Alphas in Lead Iodide B. Magness, J. Kim, C. C. Coleman Lead Iodide is a candidate for use as a room temperature gamma ray sensitive semiconductor similar to mercuric iodide. We report here on values for the energy loss factor and the stopping cross section factor in lead iodide thin films. Vapor diffused purified lead iodide was used to make thick film and thin film samples evaporated on amorphic glass substrates. Thin films were used to take advantage of the surface energy approximation. In addition, separate lead and iodide backscattering peaks from the films are well resolved. Film thickness ranged from 50nm to 1000nm as determined by optical interference methods. The high energy singly ionized helium beam was provided by the CSULA 4 MeV Van de Graff accelerator. Rutherford backscattering was detected at 170$^{\circ}$. Both the input and output energy losses were calculated from the FWHM of the corresponding peaks. The typical energy loss factor was found to be 20.2 eV/angstrom with a 3{\%} uncertainty for a 2.4 MeV input beam. As expected, this value is about one third that of the pure elements. [Preview Abstract] |
Thursday, March 24, 2005 9:12AM - 9:24AM |
U13.00007: Dislocation Pile-up/Grain Boundary Interactions Michael Dewald, William Curtin Dislocation and grain boundary migration contribute significantly to plasticity in metals, but little is understood as to how the interaction between them influence plastic response. A multiscale computational method (CADD) is used to study the effects of dislocation pile-ups on the grain boundary deformation, initiation of failure, and overall mechanical response. Use of CADD preserves accurate atomistic details while allowing a large number of dislocations to pile-up near a tilt boundary. The effects of applied loading, pile-up densities, and geometry on absorption, transmission, and damage initiation at the grain boundary are studied. [Preview Abstract] |
Thursday, March 24, 2005 9:24AM - 9:36AM |
U13.00008: Ideal Shear Strength of Silicon Under Hydrostatic Tension and Compression Ari Kay, D. C. Chrzan The ideal shear strength of silicon is computed using an {\em ab-initio} electronic structure total energy technique applying both hydrostatic tension and compression. Silicon displays a lower ideal strength under hydrostatic compression as compared with hydrostatic tension. This behavior is explained by silicon's desire to retain a more covalent like bonding under hydrostatic tension as compared with a more metallic like bonding under hydrostatic compression. The trend may be correlated with the shrinking of the band gap under the application of hydrostatic compression as compared with the gap predicted under hydrostatic tension. This research was supported by the Department of Energy, Basic Energy Sciences under the Office of Science under contract DE-AC03-76SF00098. [Preview Abstract] |
Thursday, March 24, 2005 9:36AM - 9:48AM |
U13.00009: Simulation of Current Filaments in Photoconductive Semiconductor Switches K. Kambour, Harold P. Hjalmarson, Charles W. Myles Optically-triggered, high-power photoconductive semiconductor switches (PCSS's) using semi-insulating GaAs are under development at Sandia. These switches carry current in high carrier-density filaments. The properties of these filaments can be explained by collective impact ionization theory in which energy redistribution by carrier-carrier scattering within the filament enhances the impact ionization. This allows these filaments to be sustained by fields which are relatively low compared to the bulk breakdown fields. For GaAs, the sustaining field is approximately 4.5 kV/cm. For this talk, a hydrodynamic implementation of the collective impact ionization theory is used to compute the properties of these filaments. These continuum calculations are based on previous calculations in which the steady-state properties of filaments are computed using a Monte Carlo method to solve the Boltzmann equation. The effects of defects will also be considered in the presentation of the results. [Preview Abstract] |
Thursday, March 24, 2005 9:48AM - 10:00AM |
U13.00010: A porous silicon diode as a source of low energy ($<$ 0.1 eV) free electrons and its applications Subrahmanyam Pilla, Brian Naberhuis, John Goodkind We have developed a nanoporous silicon (PS) diode that yields free electron currents with energies $<$ 0.1 eV below 77 K. The power dissipated during emission is low so that pulses of electrons can be produced below 100 mK without raising the temperature of the system. Free electrons were generated in liquid $^4$He and $^3$He as well. At 77 K, $>$ 40 nA/cm$^2$ of emission current density was obtained. The results suggest that a Poole-Frenkel type of mechanism accounts for the observed electric field enhanced conduction but the electron emission mechanism is not well understood in the present models of PS. Application of this low energy electron source in a quantum computing system using electrons on the surface of a dielectric film as well as lithography and electron microscopy will be presented. [Preview Abstract] |
Thursday, March 24, 2005 10:00AM - 10:12AM |
U13.00011: Atomic hydrogen cleaning on GaAs photocathodes Dah-An Luh The high-gradient-doping technique has been applied to GaAs photocathodes to overcome the surface-charge-limit effect while maintaining high polarization. However, the highly doped layer used in this technique is vulnerable to conventional $600^{\circ}$C heat-cleaning. One technique to reduce the heat-cleaning temperature is to use atomic hydrogen cleaning (AHC). We have systematically studied AHC using GaAs photocathodes, and have successfully reduced the heat-cleaning temperature to $450^{\circ}$C. The effect of AHC on polarization was minimal or zero in our study. In this presentation, we will show latest results from our study. Recent developments and future plans to integrate AHC into the SLAC linac injector polarized electron source will also be discussed. [Preview Abstract] |
Thursday, March 24, 2005 10:12AM - 10:24AM |
U13.00012: Towards SiC surface functionalization: an ab initio study Alessandra Catellani, Giancarlo Cicero We present a microscopic model of the interaction and adsorption mechanism of simple organic molecules on SiC surfaces as obtained from ab initio molecular dynamics simulations. Our results for the silicon terminated SiC(001) surface show that at variance with the most exploited semiconductors such as Si and GaAs, the most common functional groups chemisorb to the surface, as a consequence of the substrate polarity with exothermal reactions. The preferential chemisorption of thiolates in particular can lead to the realization of stable self-assembled monolayers, with no requirement of preliminar metallic deposition. Our results open the way to functionalization of silicon carbide, a leading candidate material for bio-compatible devices. Part of this work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. [Preview Abstract] |
Thursday, March 24, 2005 10:24AM - 10:36AM |
U13.00013: Integrability constraints for atomic-orbital integrals with applications to semi-empirical modeling of multi-element systems C. Leahy, A. Tchernatinsky, M. Yu, C.S. Jayanthi, S.Y. Wu Semi-empirical modeling of atomic-scale systems is often plagued by several issues related to atomic-orbital integrals. There are typically several sets of parameters which give similar results, suggesting that some combinations of parameters are redundant. The energy eigenvalues are not guaranteed to be real, which can and do result in systems that do not have a calculable energy. The use of $d$- orbitals results in an unreasonable increase in the number of parameters, making it difficult to model the transition metals. And the extraction of parameters for multi-element systems from those of single-element systems is not well-understood. We have improved these issues by accounting for the constraints which arise from the fact that the elements of the Hamiltonian and overlap matrix are specific integrals of specific atomic orbitals. These constraints are implemented using convolution and deconvolution between the two-center integrals and the radial parts of the orbitals. The result is a $50\%$ decrease in the relevant number of parameters for $s$ and $p$ orbitals, and a $83\%$ decrease for the $d$ orbitals. The eigenvalues are now always real. And the parameters for multi- element systems can be obtained using a convolution of the single-element orbitals, eliminating the need for artificial averaging or re-fitting techniques. [Preview Abstract] |
|
U13.00014: Investigation of the Orbital Ordering Transition in La$_4$Ru$_2$O$_{10}$ using the Mossbauer Effect Michael De Marco, Ryan Heary, Dermot Coffey, Peter Khalifah, Brian Sales, David Mandrus, Steve Toorongian, Michael Haka There is a structural phase transition in La$_4$Ru$_2$O$_{10}$ from a triclinic phase starting at 140K to a monoclinic phase which is complete by 190K. This is a accompanied by the development of a local moment from $\mu_{eff} \simeq 0.4\mu_B$ to $\mu_{eff} \simeq 2.5\mu_B$ which leads to the identification of this transition with orbital ordering. The Mossbauer Effect(ME) has been measured from 4.2K to 196K in a sample prepared with enriched $^{99}$Ru(97\%). The ME spectrum is fit with two sites consistent with the triclinic structure. The spectra for the two sites are characterized by a quadrupole splitting(QS) and an isomer shift(IS): QS$_1$=0.51mm/s and I$_1$=-0.27mm/s and QS$_2$=0.38mm/s and IS$_2$=-0.32mm/s. At 171K the sample is mostly in the monoclinic phase which has a single-site ME spectrum with QS=0.38mm/s and IS=-0.31mm/s. The less symmetric site with the larger QS has disappeared. Throughout the transition the IS is consistent with a +4 charge state for the Ru site. The Debye temperature is 307K. [Preview Abstract] |
|
U13.00015: Optimising Magnetoresistance in InSb Will Branford, Anke Husmann, Stuart Solin, Steven Clowes, Tong Zhang, Yury Bugoslavsky, Lesley Cohen The extraordinary magnetoresistance (EMR) geometry produces the highest low field MR to date. Here we address the high field MR of InSb comparing materials from several sources and studying the behaviour when processed into a set of standard and novel geometries. We find that the Corbino geometry still produces the largest high field MR, but the linearity of the high field MR in a micron thick InSb film is enhanced by the fabrication of an array of interconnected circles with high resistance bridges. Nevertheless, unprocessed submicron InSb epilayers also show enhanced linear MR properties. This work was funded by EPSRC and by NSF grant ECS-0329347. [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