Bulletin of the American Physical Society
Spring 2010 Meeting of the Ohio Section of the APS
Volume 55, Number 4
Friday–Saturday, April 30–May 1 2010; Flint, Michigan
Session B2: Condensed Matter and Semiconductors |
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Room: Campus Center Gold Room |
Saturday, May 1, 2010 8:00AM - 8:12AM |
B2.00001: Andreev Reflection Spin Polarization Measurements of a Weak Ferromagnet Pd$_{1-x}$Ni$_{x}$ Pushkal Thapa, Raghava P. Panguluri, Trupti S. Khaire, Boris Nadgorny As the magnetic moment and the spin polarization of a ferromagnetic material have distinct origins, the existence of a relationship between these two different physical quantities has always been the topic of intense debate. We have studied a series of weakly ferromagnetic variable composition Pd$_{1-x}$Ni$_{x}$ thin film samples fabricated by sputter deposition. Point Contact Andreev Reflection (PCAR) spectroscopy with electrochemically etched Nb tips was used to measure the spin polarization of these samples. Spin polarization values were obtained by fitting the conductance data with the modified BTK model. Dependence of Curie temperature and magnetization on Ni concentration was observed. Spin polarization of these samples will be compared to their magnetization (measured by a SQUID magnetometer) and the concentration of Ni; and the results will be discussed. [Preview Abstract] |
Saturday, May 1, 2010 8:12AM - 8:24AM |
B2.00002: Spin and energy relaxation of excitons in GaAs coupled quantum wells Chih-Wei Lai, Kyaw Zin Latt, Werner Dietsche We report sub-100ps exciton spin relaxation and transient splitting attributed to exchange interaction for intra-well excitons. The spin splitting and relaxation are analyzed in terms of inter-exciton and intra-exciton exchange interaction. For inter-well excitons where intra-exciton change interaction is suppressed, a spin decay-time $>$1-ns is observed at low densities. Transient exciton spin splitting and relaxation are determined from time-resolved photoluminescence (TRPL) spectroscopy and polarimetry with a streak camera system. In contrast to standard TRPL measurements based on up-conversion and pump-probe techniques, the streak-camera setup allows for speedy spectroscopy and Stokes polarimetry measurements as a function of the exciton density, and magnetic and electric fields. For 6- nm GaAs/AlGaAs quantum wells at intermediate density (a few 10$^ {10}$ cm$^{-2})$, a spin splitting of 2-meV with a decay time of $\sim$50 ps appeared instantly under a near-resonant ps pulsed excitation. For long-lived ($>$1ns) inter-well spatially indirect excitons under a cross-well electric field, intra- exciton exchange interaction is suppressed and the inter-exciton interaction is dominantly dipolar. Transient exciton energy shift and spin relaxation are characterized versus the exciton density and applied electric field under an excitation near the intra-well direct exciton transition. [Preview Abstract] |
Saturday, May 1, 2010 8:24AM - 8:36AM |
B2.00003: Ferromagnetism in ZnO-CoO multilayers Sudakar C., B. Kirby, Sanjiv Kumar, A. Dixit, R. Naik, G. Lawes, V.M. Naik The magnetic properties of CoO-ZnO heterostructures are examined to elucidate the origin of the ferromagnetic signature in Co doped ZnO. We used RF magnetron sputter deposition to prepare superlattice films with alternating layers of CoO and ZnO on sapphire substrates. The CoO and ZnO layer thickness were varied from 20 nm to 100 nm and from 75 to 225 nm, respectively. Bulk magnetization measurements show that the multilayers exhibit a ferromagnetic moment at 300 K. Saturation magnetization decreases by two orders from 5 x 10$^{-4}$ emu/cm$^{2}$ for CoO with no interface layer to 1.6 x 10$^{-5}$ emu/cm$^{2}$ with ten layers of CoO/ZnO interfacial area. To study the chemical and magnetic interaction between ZnO and CoO, the CoO/ZnO interface has been probed with Rutherford backscattering and polarized neutron reflectometery. We will present thickness measure of any magnetized interface region, and the Co magnetic moment within those regions, which allow us to test specific models for the origin of ferromagnetism in this system. [Preview Abstract] |
Saturday, May 1, 2010 8:36AM - 8:48AM |
B2.00004: Influence of a high resistivity transparent (HRT) layer on the performance of CdTe solar cells Hasitha Mahabaduge, Kristopher Wieland, Alvin Compaan Cadmium telluride (CdTe) solar cells have become very successful for large scale application of photovoltaic energy conversion with Ohio-based solar cell manufacturer, First Solar, now the largest manufacturer of thin-film cells in the world. Although CdTe solar cells have shown laboratory efficiencies in excess of 16.5{\%} its realistic potential efficiency is well above 20{\%}. High-resistivity transparent oxide buffer layers (HRT's) added between the transparent conducting oxide (TCO) and CdS layers in CdTe solar cells can enhance the performance of the device. Our results show an increase in efficiency with the HRT layer with the greatest contribution coming from improved fill factor (FF). Open circuit-voltage (V$_{oc})$ and short-circuit current (J$_{sc})$ stay relatively constant. The effect of different materials as the HRT layer on the cell structure TCO/HRT/CdS/CdTe/Cu/Au was investigated using commercially available SnO$_{2}$:F as the TCO. The study included ZnO, ZnO:Al, SiO$_{2}$, SnO$_{2}$ and Al$_{2}$O$_{3}$. Our results show that ZnO and ZnO:Al are promising candidates for the HRT layer and the use of ZnO:Al reactively sputtered with O$_{2}$ is particularly attractive since the transition from TCO to HRT is accomplished simply by adding O$_{2}$ to the Ar sputtering gas. [Preview Abstract] |
Saturday, May 1, 2010 8:48AM - 9:00AM |
B2.00005: Infrared Absorption Measurements of GaAs, GaSb, and InAs at Elevated Temperatures Thomas Harris, Shekhar Guha, Yung Yeo, Leo Gonzalez, Amelia Carpenter, Robert Hengehold Investigation of the optical and electrical behavior of Si, Ge, GaAs, GaSb, InAs, and InP at very high temperatures has not been studied much, at least not experimentally. The importance of such research becomes obvious because elevated temperatures can cause significant changes in the optical properties of the material which can degrade the performance of the device. Therefore, infrared absorption spectra of Si, Ge, GaAs, GaSb, InAs, and InP were measured from 0.6 to 25 $\mu $m at temperatures ranging from 295 up to 900 K. A Fourier Transform InfraRed (FTIR) spectrometer was used in combination with a custom-designed heater assembly. The temperature dependence of the band gaps were estimated from the transmission spectra, and they showed good agreement with the values found in the literature. For GaSb and InAs, data was taken at higher temperatures than what was seen in the literature, extending current knowledge to a higher range of temperatures. In addition to the band gap change as a function of temperature, free-carrier absorption was also observed. [Preview Abstract] |
Saturday, May 1, 2010 9:00AM - 9:12AM |
B2.00006: Non-Adiabatic Molecular Dynamics of B+H2 David Weeks, Luke Barger Adiabatic potential energy surfaces for the B+H2 system are used together with derivative coupling terms to compute diabatic potential energy surfaces. The diabatic surfaces are then expanded in terms of Legendre polynomials and represented in a mixed angular momentum, radial coordinate basis. This matrix representation of the potential is combined with the nuclear kinetic energy to yield a set of coupled differential equations that describe the non-adiabatic dynamics of B+H2. This dynamics is explored using numerical wave packet propagation. [Preview Abstract] |
Saturday, May 1, 2010 9:12AM - 9:24AM |
B2.00007: Band-edge enhancement of magneto-optical rotation in a 1-d polymer lattice Michael Crescimanno, James Andrews, Guilin Mao, Aaron Bishop, Kyle Comeau, Ryan Livingston, Bijayandra Shakya Faraday rotation, the rotation of the polarization of light propagating along an applied magnetic field, can be enhanced by modifying the dispersion relationship. We develop the theory and computational tools necessary to understand the enhancement measured in recent experiments conducted at YSU using a multilayer of polystyrene and PMMA prepared by the CLiPS NSF Center at CWRU. [Preview Abstract] |
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