Bulletin of the American Physical Society
2008 Joint Fall Meeting of the Texas and Four Corners Sections of APS, AAPT, and Zones 13 and 16 of SPS, and the Societies of Hispanic & Black Physicists
Volume 53, Number 11
Friday–Saturday, October 17–18, 2008; El Paso, Texas
Session E2: Condensed Matter: Spectroscopy |
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Chair: J.R. Dennison, Utah State University Room: Union East, 3rd Floor Ray |
Friday, October 17, 2008 3:30PM - 3:42PM |
E2.00001: Raman and infrared studies of synthetic Maya Blue pigment Layra Reza, Felicia Manciu, Alejandra Ramirez, Russell Chianelli A fascinating aspect of \textit{Maya pigments} is that despite the environmentally harsh humidity and high temperatures they resist fading and they have unprecedented stability. In this investigation, we address the question of how organic dye binds to inorganic palygorskite to form a pigment similar to \textit{Maya Blue}. We also address how such binding might be affected by varying the proportion of dye relative to that of the mineral, and by varying the length of heating time used in preparation of the pigment. Our analysis by Raman and infrared absorption spectroscopies proves the partial elimination of the selection rules for the centrosymmetric indigo, and shows the disappearance of the indigo N-H bonding, as the organic molecules incorporate into palygorskite material. Infrared data confirm the loss of zeolitic water and a partial removal of structural water after the heating process. Evidence of bonding between palygorskite and indigo through oxygen is revealed by both spectroscopic measurements. [Preview Abstract] |
Friday, October 17, 2008 3:42PM - 3:54PM |
E2.00002: Simulated models of inhomogeneous broadening in perturbed angular correlation spectroscopy Jeffery A. Hodges, Tyler Park, Michael Stufflebeam, W. Evenson, P. Matheson, M.O. Zacate All real crystals have defects such as impurities and vacancies which affect their properties. In perturbed angular correlation (PAC), these defects produce damping of the correlation signal in time and broadening of the frequency spectrum. This broadening is termed ``inhomogeneous broadening'' since it is due to the inhomogeneities (i.e. defects) in the crystal. We have simulated PAC spectra for various concentrations (0.1\% to 15\%) of randomly distributed defects with a near-neighbor vacancy in simple cubic and face-centered cubic crystal structures. For every particular set of defects, the randomly distributed defects and the near-neighbor vacancy together produce a net electric field gradient (EFG), from which we obtain the PAC spectrum. We then average PAC spectra to study the effects of defect concentration and crystal structure on inhomogeneous broadening as an aid to analyzing experimental data. This work will be applied initially to broadened PAC data from $\beta$-Mn, Al-doped $\beta$-Mn, and Sr$_2$RuO$_4$. [Preview Abstract] |
Friday, October 17, 2008 3:54PM - 4:06PM |
E2.00003: Independent component analysis of inhomogeneous broadening in perturbed angular correlation spectroscopy Michael Stufflebeam, Jeffery A. Hodges, Tyler Park, W. Evenson, P. Matheson, M.O. Zacate Independent component analysis (ICA) of electric field gradient (EFG) tensor components has proven useful in analysis of inhomogeneous broadening in perturbed angular correlation (PAC). We have simulated PAC spectra for various concentrations (0.1\% to 15\%) of randomly distributed defects with a near- neighbor vacancy in simple cubic and face-centered cubic crystal structures. In analyzing this simulation, we used ICA to transform the $V_{xx}$ and $V_{zz}$ EFG components to find a joint probability distribution function for the EFGs. ICA allowed us to separate the components and develop the joint probability function as a product of the probability distributions for two independent coordinates. Then we found the broadened $G_2(t)$ by integration over the joint probability distribution function. We have compared these results to simulated $G_2(t)$ functions, allowing us to analyze the concentration dependence of the broadened PAC spectrum. This work will be applied initially to broadened PAC data from $\beta$-Mn, Al-doped $\beta$-Mn, and Sr$_2$RuO$_4$. [Preview Abstract] |
Friday, October 17, 2008 4:06PM - 4:18PM |
E2.00004: Concentration dependence of inhomogeneous broadening in perturbed angular correlation spectroscopy Carlos Moreno, Jeffery A. Hodges, Tyler Park, Michael Stufflebeam, W. Evenson, P. Matheson, M.O. Zacate Since real crystals always include defects, the effect of the defects on crystal properties depends on how many defects are present, i.e. on defect concentration. In perturbed angular correlation (PAC), these defects produce damping of the correlation signal in time and broadening of the frequency spectrum. This ``inhomogeneous broadening'' depends quantitatively on defect concentration, so the size of the broadening in a PAC spectrum can be a measure of the concentration of defects. Using simulated PAC spectra and independent component analysis to obtain the probability distribution function for electric field gradient (EFG) components, we have found defect concentration-dependent parameters for the probability functions. This allows us to calculate broadened PAC spectra for any selected defect concentration. It also allows us to fit defect concentration from an experimental PAC spectrum. This work will be applied initially to broadened PAC data from $\beta$-Mn, Al-doped $\beta$-Mn, and Sr$_2$RuO$_4$. [Preview Abstract] |
Friday, October 17, 2008 4:18PM - 4:30PM |
E2.00005: Nuclear relaxation of $N$-state symmetric models Tyler Park, Jeffery A. Hodges, Carlos Moreno, Michael Stufflebeam, W. Evenson, P. Matheson, M.O. Zacate Nuclear relaxation of perturbed angular correlation (PAC) spectra offers insights to diffusion because it arises from motion of defects or of a nuclear probe in a crystal. The $N$-state symmetric model is a model of fluctuation among $N$ symmetric electric field gradients (EFGs) experienced by a radioactive nuclear probe. By simulating the $N$-state symmetric model for various rates of hopping among the $N$ EFGs, the resulting spectra can be fitted with a damped perturbation function, $G_{22}(t)$, or an exponential decay function to find the decay constant ($\lambda$). By plotting $\lambda$ against the hopping rate, we find the maximum relaxation point. Fitting the raw spectrum, a spectrum weighted by error bars, and a spectrum with simulated errors gives a good indication of the relaxation that would be observed in a PAC experiment. The maximum relaxation point can then be used as an experimental measure of the defect or probe hopping rate, and hence the diffusion rate at that temperature. We report the results of our simulations and their implications, with potential applications to diffusion in intermetallic systems. [Preview Abstract] |
Friday, October 17, 2008 4:30PM - 4:42PM |
E2.00006: Defect state investigation of amorphous silicon carbide using electron spin resonance and photothermal deflection spectroscopy Brian J. Simonds, J. Gallon, Tining Su, Arun Madan, P. Craig Taylor Amorphous silicon carbide alloys are being discussed as a possible top photovoltaic layer in photo electro-chemical cells used for water splitting. In order to be used as such, it is important that the effect of carbon concentration has on bonding, and thus the electronic and optical properties, is well understood. Electron spin resonance experiments, under varying experimental conditions, were performed to study the dangling bonds, which were found to be dominantly at the silicon atoms in these films. At room temperature, the spin count densities varied between 10$^{16}$ and 10$^{18}$ spins/cm$^{3}$. Photothermal deflection spectroscopy experiments were also performed in order to look at defects resulting in sub band-gap absorption where absorption is defined proportional to e$^{E/E'}$ with E' the inverse slope of the Urbach tail. We report slopes of between 70 meV to 83 meV. These increases in inverse slope correlate with increases in spin density. [Preview Abstract] |
Friday, October 17, 2008 4:42PM - 4:54PM |
E2.00007: Nuclear polarization effects on electron spin resonances as observed by Kerr rotation Benjamin Heaton, John Colton Magnetic resonances between electron spin states in doped GaAs layers has been studied by optically detected Kerr rotation signals. Electron resonance signals are strongly dependent on local nuclear polarizations. Nuclear polarization effects can be controlled, and total nuclear polarization has a decay time of 2.7 minutes. [Preview Abstract] |
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