Bulletin of the American Physical Society
2009 Spring Meeting of the Texas Sections of the APS, AAPT, and SPS
Volume 54, Number 2
Thursday–Saturday, April 2–4, 2009; Stephenville, Texas
Session G2: APS2 |
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Room: Science Building 109 |
Friday, April 3, 2009 3:00PM - 3:12PM |
G2.00001: Characterization of the Muonium Defect in Cz-Si$_{0.09}$Ge$_{0.91}$ Brent Carroll, Roger Lichti, Philip King, Gurkan Celebi, Kim Chow, Ichiro Yonenaga The Muonium (Mu) [0/-] transition energy level is predicted to become valance band resonant in the Silicon Germanium alloy system for a Ge content of roughly 92{\%}. The comparison of observations from various Muon Spin Research (MuSR) techniques indicate a Mu signal consistent with a shallow acceptor state. We report our MuSR measurements of diamagnetic and paramagnetic Muonium states in Czochralski grown Si$_{0.09}$Ge$_{0.91}$ as part of an on-going effort to characterize the Mu shallow acceptor as well as testing the prediction of a universal Hydrogen (Muonium) defect level. Muonium states have been examined by means of Transverse Field (TF), Longitudinal Field (LF), and Radio Frequency (RF) MuSR techniques that provide information on Mu charge states, hyperfine distributions, and motional properties. Characterization of the ubiquitous H defect is important in the development of high mobility components of novel transistors and optoelectronic devices based on SiGe alloy heterojunctions. [Preview Abstract] |
Friday, April 3, 2009 3:12PM - 3:24PM |
G2.00002: High Temperature Phase Transitions in RbH2PO4 Heber Martinez, Cristian Botez, Ron Tackett, Russell Chianelli MH2PO4 (M=Cs, Rb) solid acids exhibit a several-order-of-magnitude increase in proton conductivity upon heating above a temperature threshold [1, 2]. This behavior allows these solid acids to function as fuel-cell electrolytes at intermediate temperatures [3]; this has attracted much interest. We studied the structure of RDP when heated within the 25-250\r{ }C range. We used temperature- and time-resolved powder XRD on powder RDP. Our XRD data, evidenced a tetragonal to monoclinic transition that occurs within the 90-110\r{ }C interval. Rietveld refinements demonstrate that the newly observed monoclinic structure is a RDP polymorph. This suggests that the superprotonic behavior in RDP might be triggered by a monoclinic-cubic polymorphic transition \textit{similar }to the one observed in CsH2PO4. Further heating of the sample, under ambient pressure and humidity conditions, results in dehydration. A possible method to avoid dehydration in future research is to carry out the heating on samples subjected to high pressures of about 1GPa [1,2,4]. [1] Boysen \textit{et al., }Chem. Mater. \textbf{15, }727(2003). [2] Boysen \textit{et al., }Chem. Mater. \textbf{16, }693(2004). [3] Boysen et al., Science \textbf{303, }68(2004). [4] Botez et al., J. Chem. Phys. \textbf{127, }194701(2007) [Preview Abstract] |
Friday, April 3, 2009 3:24PM - 3:36PM |
G2.00003: Nanotubes in polar solvents: Solvation and physical properties of excess charge carriers Geoffrey Ussery, Yuri Gartstein An excess charge carrier added to a one-dimensional (1D) semiconductor immersed in a polar solvent can undergo self- localization into a large-radius adiabatic polaron whose physical properties differ significantly from band states. Using a simplified theoretical model for small-diameter tubular structures immersed in a 3D polarizable solvent, we explore some testable signatures of these solvation-induced polarons. We discuss optical (infrared) absorption due to transitions between localized electronic states formed in the self-consistent polarization potential well, local dielectric relaxation modes around the polaron, and its mobility. Numerical estimates indicate that the dissipative drag of the polar environment can reduce the mobility by orders of magnitude in comparison with intrinsic values. Thermal fluctuations of the medium also cause a substantial broadening of the local optical absorption from the polaron. For more detail, see Yu. N. Gartstein and G. L. Ussery, Phys. Lett. A, 372, 5909 (2008) and G. L. Ussery and Yu. N. Gartstein, J. Chem. Phys., 130, 014701 (2009). [Preview Abstract] |
Friday, April 3, 2009 3:36PM - 3:48PM |
G2.00004: Influence of Magnetic Molecules on Electron Spin Scattering in InAs as Seen in Its Low Temperature Magnetoresistance Joseph Gilpin, Victoria Soghomonian, Jean Heremans, Raymond Kallaher Quantum interference between different scattering trajectories of electrons in solid-state systems leads to corrections to the classically predicted electrical resistivity. InAs films were studied, focusing on the influence of a monolayer of the magnetic molecule, Mn12, on the spin scattering of the electrons in the InAs accumulation layer. The weak localization and anti localization phenomena were examined via comparison of the magneto-resistance, as predicted by Bergman.\footnote{Bergmann, G. (1984). Weak Localization In Thin Films: a time-of-flight experiment with conduction electrons. \textit{Physics Reports (Review Section of Physics Letters)} (107), 1-58.} The localization effects were measured at temperatures of 0.4 K. Through the study of the characteristic localization effects it is possible to determine the existence and effect of the quantum scatterings. In initial experiments clear anti-localization is observed, but the trends have not yet yielded systematic and consistent answers correlating the effect of the Mn12 monolayer to the spin scattering in the InAs layer. Future refinement of our system of Mn12 application better suited to the delicate InAs surface is expected to produce clearer evidence of the localization phenomena, and subsequently insight into scattering effects. [Preview Abstract] |
Friday, April 3, 2009 3:48PM - 4:00PM |
G2.00005: Coherent control of elastic and Raman fluorescence channels in 3-level system Shaoyan Gao, Olga Kocharovskaya We consider a 3-level atomic system interacting with two coherent fields in the ladder configuration. Namely, the probe field couples the ground and first excited state while the driving field interacts with two excited states. In the case of sufficiently strong driving field the fluorescence intensity at the Raman transition may greatly exceed the intensity in the elastic channel even when the decay rates for both channels are equal. The effect is due to quantum interference in fluorescence. In the dressed state basis, quantum interference is constructive in the Raman transition and destructive in the elastic channel. [Preview Abstract] |
Friday, April 3, 2009 4:00PM - 4:12PM |
G2.00006: Intensity analysis and energy-level modeling of Nd$^{3+}$ in Nd$^{3+}$:Y$_{2}$O$_{3}$ nanocrystals in polymeric hosts Robert Dennis, Kelly Nash, Dhiraj Sardar, John Gruber Optical absorption and emission intensities are investigated for Nd$^{3+}$ in nanocrystalline Nd$^{3+:}$Y$_{2}$O$_{3}$. Room temperature absorption intensities of Nd$^{3+}$(4$f^{3})$ transitions in synthesized Nd$^{3+:}$Y$_{2}$O$_{3 }$nanocrystals have been analyzed using the Judd-Ofelt (J-O) approach to obtain the phenomenological intensity parameters. The J-O intensity parameters are used to calculate the spontaneous emission probabilities, radiative lifetimes, and branching ratios of the Nd$^{3+}_{ }$transitions from the upper multiplet manifolds to the corresponding lower-lying multiplet manifolds $^{2S+1}L_{J}$ of Nd$^{3+}$(4$f^{3})$. The emission cross sections and room temperature fluorescence lifetimes of the important intermanifold $^{4}F_{3/2} \quad \to $ $^{4}I_{J }$(J=9/2, 11/2, 13/2, 15/2)$_{ }$transitions have been determined. We also compare the spectra of the Nd$^{3+}$:Y$_{2}$O$_{3}$ nanocrystals to those of the nanocrystals embedded in polymeric matrices of epoxy and chitosan, and we find similarities in terms of the detailed Stark energy levels of the Nd$^{3+ }$ion in the Y$_{2}$O$_{3}$ nanocrystalline host. The 300 K spectra$_{ }$are analyzed for the energy (Stark) level transitions between the $^{2S+1}L_{J}$ multiplet manifolds of Nd$^{3+}$(4$f^{3})$. The results of this study are also compared with a crystal-field splitting analysis reported earlier for single-crystal Nd$^{3+}$:Y$_{2}$O$_{3}$ grown by a modified flame fusion method. [Preview Abstract] |
Friday, April 3, 2009 4:12PM - 4:24PM |
G2.00007: Development of a Simple Positron Age-Momentum Setup Thomas Sheffield, C.A. Quarles A positron age-momentum setup that uses NIM Bin electronic modules and a conventional multichannel analyzer (MCA) is described. The essential idea is to accumulate a Doppler broadened spectrum (sensitive to the annihilation electron momentum) using a high purity Germanium detector in coincidence with a BaF2 scintillation counter, which also serves as the stop signal in a conventional positron lifetime setup. The MCA that collects the Doppler spectrum is gated by a selected region of the lifetime spectrum. Thus we can obtain Doppler broadening spectra as a function of positron lifetime: an age-momentum spectrum. The apparatus has been used so far to investigate a ZnO sample where the size of different vacancy trapping sites may affect the positron lifetime and the Doppler broadening spectrum. We are also looking at polymer and rubber carbon-black composite samples where differences in the Doppler spectrum may arise from positron trapping or positronium formation in the samples. Correction for background and contribution from the positron source itself to the Doppler spectrum will be discussed. [Preview Abstract] |
Friday, April 3, 2009 4:24PM - 4:36PM |
G2.00008: Addition of Adapted Optics towards obtaining a quantitative detection of diabetic retinopathy Brian Yust, Isidro Obregon, Andrew Tsin, Dhiraj Sardar An adaptive optics system was assembled for correcting the aberrated wavefront of light reflected from the retina. The adaptive optics setup includes a superluminous diode light source, Hartmann-Shack wavefront sensor, deformable mirror, and imaging CCD camera. Aberrations found in the reflected wavefront are caused by changes in the index of refraction along the light path as the beam travels through the cornea, lens, and vitreous humour. The Hartmann-Shack sensor allows for detection of aberrations in the wavefront, which may then be corrected with the deformable mirror. It has been shown that there is a change in the polarization of light reflected from neovascularizations in the retina due to certain diseases, such as diabetic retinopathy. The adaptive optics system was assembled towards the goal of obtaining a quantitative measure of onset and progression of this ailment, as one does not currently exist. The study was done to show that the addition of adaptive optics results in a more accurate detection of neovascularization in the retina by measuring the expected changes in polarization of the corrected wavefront of reflected light. [Preview Abstract] |
Friday, April 3, 2009 4:36PM - 4:48PM |
G2.00009: Two-level trap model of BEC in an ideal gas Konstantin Dorfman, Vitaly Kocharovsky, Vladimir Kocharovsky We consider a two-energy-level trap with arbitrary degeneracy of an upper level and find an analytical solution for the condensate statistics in a mesoscopic ideal gas with arbitrary number of atoms and any temperature, including a critical region. The solution is a cut-off negative binomial distribution that tends to a cut-off gamma distribution in the thermodynamic limit. We show how to model BEC in real traps by BEC in the two-level or three-level traps. [Preview Abstract] |
Friday, April 3, 2009 4:48PM - 5:00PM |
G2.00010: Microwave Initiated Atomic Spectra from Select Atomic Species James Roberts, Jai Dahiya, Aman Anand, Rick Croley Quantum states were energized in gaseous Helium ($^{3}$He and $^{4}$He) using a 2.45 GHz magnetron coupled to the gases. A residual gas analyzer was used to determine the mass of each species. An Ocean Optics Optical Spectrometer collected the light via an optic probe. The data show unique spectral emission line shapes. Data using both computational as well as theoretical techniques are presented. Traditional high voltage arc discharge data were taken for the gas species to compare with microwave stimulated atomic emissions. [Preview Abstract] |
Friday, April 3, 2009 5:00PM - 5:12PM |
G2.00011: Spectroscopic Analysis of Nd$^{3+}$:Y$_{2}$O$_{3}$ Nanocrystals in Polymers and Copolymers Nathan Ray, Kelly Nash, Robert Dennis, John Gruber, Dhiraj Sardar, Mao Gen Zhang Spectroscopic properties of nanocrystalline Nd$^{3+}$ in Nd$^{3+}$:Y$_{2}$O$_{3 }$embedded in solid plastic hosts (2-hydroxyethyl methacrylate (HEMA) and copolymer of HEMA/styrene) are characterized. The standard Judd-Ofelt model has been applied to the room temperature absorption intensities of Nd$^{3+}$(4$f^{3})$ transitions in the plastic hosts to determine the three phenomenological intensity parameters: \textit{$\Omega $}$_{2}$, \textit{$\Omega $}$_{4}$, and \textit{$\Omega $}$_{6}$. Intensity parameters are then utilized to determine the radiative decay rates and branching ratios of the Nd$^{3+}$(4$f^{ 3})$ transitions from the upper manifold state $^{4}F_{3/2}$ to the lower-lying multiplet manifolds $^{4}I_{J }$(J= 9/2, 11/2, 13/2, 15/2). Emission cross sections and room temperature fluorescence lifetimes of the important intermanifold $^{4}F_{3/2} \quad \to \quad ^{4}I_{J }$(J=9/2, 11/2, 13/2)$_{ }$transitions are determined. We investigate the detailed crystal-field splitting of the energy levels of the Nd$^{3+ }$ion in the Y$_{2}$O$_{3}$/polymer host. The 300 K spectra$_{ }$are analyzed for the energy level transitions between the $^{2S+1}L_{J}$ multiplet manifolds of Nd$^{3+}$(4$f^{3})$. Results are also compared with a crystal-field splitting analysis reported earlier for single-crystal Nd$^{3+}$:Y$_{2}$O$_{3}$. [Preview Abstract] |
Friday, April 3, 2009 5:12PM - 5:24PM |
G2.00012: Using a Microwave Cavity to Study Select Gas-Nanomaterials Absorption/Adsorption James Roberts, Jai Anand, Aman Anand Complex perturbation response of gas molecules and Single Walled Carbon Nanotubes(SWCNT)loaded in microwave resonant cavity operating in TE$_{011}$ mode is presented in this talk. A microwave network analyzer was used with the resonant frequency (9.1-9.8 GHz) to demonstrate selective adsorption response of SWCNT for CO, CO$_{2, }$O$_{2 }$and H$_{2}$. Van der Waals' and columbic forces were studied for a specific degree of affinity by SWCNTs towards select gases. Slater's Perturbation theory, the Claussius-Mossotti and Langevin-Debye relationships were used in understanding the interaction of the gases with nanomaterials. From these results a chemical-biological sensor prototype was developed. The method proposed is to develop operational sensors to detect toxin gases for homeland security and to develop ``sniffers'' to detect toxin drugs. [Preview Abstract] |
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