Bulletin of the American Physical Society
78th Annual Meeting of the Southeastern Section of the APS
Volume 56, Number 9
Wednesday–Saturday, October 19–22, 2011; Roanoke, Virginia
Session PC: Condensed Matter Physics/Nanophysics II |
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Chair: Wilfredo Otano Rivera, University of Puerto Rico-Cayey Room: Crystal Ballroom C |
Saturday, October 22, 2011 10:45AM - 10:57AM |
PC.00001: Determination of the Current Voltage Signatures of NanoGUMBOS Kalyan Kanakamedala, Sergio De Rooy, Susmita Das, Bilal El-Zahab, Isiah Warner, Theda Daniels-Race Tantamount to the realization of next generation nanoscale devices is the synthesis and characterization of new electronic materials. GUMBOS, or a \textbf{G}roup of \textbf{U}niform \textbf{M}aterials \textbf{B}ased on \textbf{O}rganic \textbf{S}alts, represent a first-time synthesis of nanoscale material composed of ionic liquid species in the frozen (solid) state whose electronic characteristics are indicative of potential future application to device electronics. Using a Keithley 4200 semiconductor characterization system, we have examined the nanoscale conductivity and current-voltage (I-V) characteristics of GUMBOS nanowires under both aqueous and ``dry'' conditions. Just as nanoGUMBOS are new materials in the realm of ionic liquid research, our I-V measurements are a first-time characterization of this species of nanostructures. [Preview Abstract] |
Saturday, October 22, 2011 10:57AM - 11:09AM |
PC.00002: Characterization of NanoGUMBOS Using Conductive Probe Atomic Force Microscopy Naveen Jagadish, Sergio De Rooy, Atiya Jordan, Ashleigh Wright, Susmita Das, Bilal El-Zahab, Isiah Warner, Theda Daniels-Race In our work on hybrid (organic-inorganic) electronic materials (HEMs), we have developed a reasonably facile method for characterizing GUMBOS or a \textbf{G}roup of \textbf{U}niform \textbf{M}aterials \textbf{B}ased on \textbf{O}rganic \textbf{S}alts. In addition to the versatility of traditional ionic liquids (i.e.-solubility, melting point, viscosity), nanoGUMBOS are functionalizable to exhibit properties such as fluorescence, magnetic susceptibility, and even antimicrobial activity. However, given our interest in the electrical properties of HEMs, we have made first-time measurements of nanoGUMBOS, using CP-AFM, in order to deduce their room temperature current-voltage characteristics. In conjunction with the nanoscale imaging of AFM alone, we have observed both the morphology and conductivity of these unique materials. Our results bode well for combining GUMBOS with substrates of more traditional materials, such as metals or semiconductors, to serve as the basis for future HEMs-based devices. [Preview Abstract] |
Saturday, October 22, 2011 11:09AM - 11:21AM |
PC.00003: Negative coefficient of thermal expansion in (epoxy resin)/(zirconium tungstate) nanocomposites Erich See, Vladimir Kochergin, Lauren Neely, Madrakhim Zayetnikov, Gianluigi Ciovati, Hans Robinson The $\alpha $-phase of zirconium tungstate (ZrW$_{2}$O$_{8})$ has the remarkable property that its coefficient of thermal expansion (CTE) takes on a nearly constant negative value throughout its entire range of thermal stability (0 -- 1050 K). Composites of ZrW$_{2}$O$_{8}$ nanoparticles and polymer resins have a reduced CTE compared to the pure polymer, but previous work has been restricted to measurements near room temperature. We show that the CTE of such composites can take on increasingly negative values as the temperature is lowered to cryogenic values. We used this phenomenon to fabricate a metal-free all-optical cryogenic temperature sensor by coating a fiber optic Bragg grating with the nanocomposite. This sensor has a sensitivity at 2 K that is at least six time better than any previous fiber-optic temperature sensor at this temperature. [Preview Abstract] |
Saturday, October 22, 2011 11:21AM - 11:33AM |
PC.00004: Towed-grid system for production and calorimetric study of homogenous quantum turbulence Roman Ciapurin, Kyle Thompson, Gary G. Ihas The decay of quantum turbulence is not fully understood in superfluid helium at milikelvin temperatures where the viscous normal component is absent. Vibrating grid experiments performed periously produced inhomogeneous turbulence, making the results hard to interpret. We have developed experimental methods to produce homogeneous isotropic turbulence by pulling a grid at a variable constant velocity through superfluid 4He. While using calorimetric technique to measure the energy dissipation, the Meissner effect was employed to eliminate all heat sources except from turbulent decay. A controlled divergent magnetic field provides the lift to a hollow cylindrical superconducting actuator to which the grid is attached. Position sensing is performed by measuring the inductance change of a coil when a superconductor, similar to that of the actuator, is moved inside it. This position sensing technique proved to be reliable under varying temperatures and magnetic fields, making it perfect for use in the towed-grid experiment where a rise in temperature emerges from turbulent decay. Additionally, the reproducible dependency of the grid's position on the applied magnetic field enables complete control of the actuator's motion. [Preview Abstract] |
Saturday, October 22, 2011 11:33AM - 11:45AM |
PC.00005: Radiative Polaritons in Thin Oxide Films with Experimental and Simulated Dispersion Relations Anita Vincent-Johnson, James Hammonds Jr., Giovanna Scarel Our research focuses on polaritons, or infrared (IR) photon-phonon coupling in ionic materials, as a way to capture IR radiation from the solar spectrum. Radiative polaritons (RP) have the unique property that their phase velocity is faster than the speed of light. We wish to prove that the polaritons present in thin oxide films are RP's with the traits predicted by theory. Therefore, in this work we study simulated and experimental IR spectra of Al$_{2}$O$_{3}$ films grown by atomic layer deposition (ALD) on Al. Since RP's are characterized by a complex frequency, $\omega$, we have derived from IR spectra the real part, Re($\omega$), as the peak centroid, and the imaginary part, Im($\omega$), as the peak's width. Dispersion relations were obtained by plotting Re($\omega$) and Im($\omega$) versus the angle of incidence of the polarized IR radiation. The agreement between simulated and experimental data and between our data and theory allow us to conclude that RP's are present in thin oxide films. [Preview Abstract] |
Saturday, October 22, 2011 11:45AM - 11:57AM |
PC.00006: Inductive Critical Currents in Nb/Mo bilayers Phillip Broussard, James Veldhorst We have carried out measurements of inductive critical currents in Nb/Mo bilayers. The films were grown by magnetron sputtering onto silicon substrates from separate sources. Sequences with varying either the molybdenum or niobium layer thickness were grown and studied. Inductive critical currents were measured using a third harmonic technique at 1 kHz. $J_{c}$ varies as $(1-t)^{3/2}$ as expected from Ginzburg-Landau theory (here $t$ is the reduced temperature, $T/T_{c}$). Measurements in low magnetic field (below 120 Gauss) show a marked decrease in $J_{c}$ with applied magnetic field. We look at various ways to interpret the $V_{3f}$ vs. drive current mentioned in the literature and compare to our results for pure niobium and the bilayers. [Preview Abstract] |
Saturday, October 22, 2011 11:57AM - 12:09PM |
PC.00007: Time-dependent hydrogen annealing of Mg-doped GaN Ustun Sunay, Mary Zvanut, Jamiyanaa Dashdorj Unintentional doping by hydrogen is a concern for industrial growth of p-type GaN which is important in creating blue LEDs and high frequency devices. Using electron paramagnetic resonance (EPR) we investigated hydrogen passivation in p-type nitrides. Samples included conventional GaN and Al$_{x}$Ga$_{1-x}$N(x=0.12,0.28) grown by chemical vapor deposition (CVD) with 1-4x10$^{19}$ cm$^{-3}$ Mg and GaN grown by Metal Modulation Epitaxy (MME) yielding 1.5x10$^{20}$ cm$^{-3}$ Mg. The Mg signal was observed during isothermal anneals in N$_{2}$:H$_{2}$ (92{\%}: 7{\%}). The Mg EPR signal unexpectedly increased below 600$^{\circ}$C in GaN, but no changes were observed in AlGaN. The MME Mg EPR signal began decreasing after 10 min at 400$^{\circ}$C, while the Mg intensity of AlGaN did not start reducing until 500$^{\circ}$C. As expected the Mg EPR signal in the CVD GaN quenched at 700$^{\circ}$C, as did the signal in AlGaN. However, the intensity of the Mg signal in MME samples was eliminated after only 20 min at 500$^{\circ}$C. The different temperature dependence suggests that hydrogen diffusion is affected by increased Mg concentration. These studies are integral for the advancement of p-type GaN. [Preview Abstract] |
Saturday, October 22, 2011 12:09PM - 12:21PM |
PC.00008: First-principles study of surface states of topological insulators Kyungwha Park Recently, three-dimensional topological insulators (TIs) with time reversal symmetry draw attention due to their unique quantum properties and device applications. Strong spin-orbit coupling in TIs induces metallic surface states within bulk band gaps. It has been known that Bi$_2$Te$_3$, Bi$_2$Se$_3$, and Sb$_2$Te$_3$ are TIs possessing a single Dirac cone in the dispersion of the surface states at a given surface. The surface states of TIs play a critical role in proposed novel physical phenomena and applications. We investigate the surface states of thin films of Bi$_2$Te$_3$(111) and Bi$_2$Se$_3$(111) using density-functional theory including spin-orbit coupling. We identify the surface states of the TI films from calculated band structures using the decay length of the surface states and electron density plots. We also present the electronic properties of the surface states of the films. [Preview Abstract] |
Saturday, October 22, 2011 12:21PM - 12:33PM |
PC.00009: Electronic Structure Determination of the Thermoelectric CuRh$_{1-x}$Mg$_{x}$O$_{2}$ using Soft X-Ray Spectroscopies Eric Martin, Paolo Vilmercati, Christine Cheney, Takao Sasagawa, Norman Mannella Magnesium-doped rhodium oxides with formula unit CuRh$_{1-x}$Mg$_{x}$O$_{2}$ and delafossite-type structure exhibit a high thermoelectric figure of merit at elevated temperatures. The electronic structure of CuRh$_{1-x}$Mg$_{x}$O$_{2}$ has been studied with x-ray emission spectroscopy (XES), x-ray absorption spectroscopy (XAS), and photoemission spectroscopy (PES). The data reveal that the states at the Fermi level are Rh-derived. Measurements carried out by changing the orientation of the linear photon polarization further indicate that the Rh states have a more localized character along the c-axis, consistent with the layered crystal structure. Given the similarity of the electronic configurations of Co and Rh, these data provide solid experimental evidence that the orbital degrees of freedom of the d$^{6}$ ionic configuration of the states rooted in transport are key for explaining the thermoelectric properties of oxide materials. [Preview Abstract] |
Saturday, October 22, 2011 12:33PM - 12:45PM |
PC.00010: Energy Band Gap Behavior as a Function of Optical Electronegativity for Semiconducting and Insulating Binary Oxides Kristen Dagenais, Matthew Chamberlin, Costel Constantin A relationship between energy band gap and electronegativity has long been understood to exist. However, defining the relationship between the two for binary oxide systems has proven difficult. Many scientists tried to model the band gap as a function of Pauling electronegativity values, but we show that by using a new concept called ``optical electronegativity'' one can obtain much better predictions regarding band gaps of new oxide. Interestingly we found that the behavior of oxides varies across depending on the chemical group the cation is from. With that knowledge, we developed two equations to describe the alkali earth metal and poor metal oxide. By using our models, we are able to predict the band gap of radium oxide at 5.36 eV. Due to the contributions of `d' and `f' orbitals we could not model lanthanide rare earth and transition metal oxides but rather we found that band gaps for both lay beween 3.56 - 5.72 eV, and 1.82 -- 3.82 eV, respectively. [Preview Abstract] |
Saturday, October 22, 2011 12:45PM - 12:57PM |
PC.00011: ABSTRACT WITHDRAWN |
Saturday, October 22, 2011 12:57PM - 1:09PM |
PC.00012: Microstructural investigations of 0.2{\%} carbon content steel Sajjad Tollabimazraehno, Kurt Hingerl The effect of thermal annealing to get different phases on low carbon steel was investigated. Steel sheets (0.2 wt. {\%} C) of 900 $\mu $m thickness were heat treated to produce different structures. All the samples have the same starting point, transformation to coarse austenite at 900 degree Celsius. ~The nano indentation results revealed that samples have different hadness. By making conventional SEM micrographs, focus ion beam maps, and Electron backscatter diffraction (EBSD) the microstructural development and grain boundary variation of transformed phases martensite, biainte, tempered martensite and different combination of these phases were studied. [Preview Abstract] |
Saturday, October 22, 2011 1:09PM - 1:21PM |
PC.00013: Optical interferometric assessment of thin-film adhesion to substrate Sushovit Adhikari, Kenji Gomi, Sanichiro Yoshida A Michelson interferometer has been assembled to evaluate the adhesion strength of thin-film coating on silicon wafers. Two gold coated silicon wafer specimens are configured as the two end mirrors of the interferometer. The end mirrors are slightly tilted so that vertical interferometric fringes (dark stripes) are formed behind the beam splitter. An acoustic transducer is attached to the silicon substrate of each wafer so that the gold coated surface oscillates in the direction of the optical axis. One wafer is driven at a time. As the coated surface oscillates, the vertical fringes oscillate horizontally, where the amplitude of the oscillation varies depending on the adhesion strength. Two specimens, one with oxygen-plasma pre- coating treatment and the other with no pre-coating treatment, have been tested. Empirically, the former is known to be stronger in adhesion than the latter. When the specimen of the weaker adhesion is driven in a range of 10 -- 17 kHz, the fringes become blurry, indicating that displacement is greater. Analysis of the fringe patterns in the spatial frequency domain has enabled us to differentiate the displacement quantitatively. [Preview Abstract] |
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