Bulletin of the American Physical Society
79th Annual Meeting of the APS Southeastern Section
Volume 57, Number 16
Wednesday–Saturday, November 14–17, 2012; Tallahassee, Florida
Session CC: Condensed Matter Physics I |
Hide Abstracts |
Chair: David Hilton, University of Alabama-Birmingham Room: DoubleTree Adams-Park |
Thursday, November 15, 2012 10:45AM - 10:57AM |
CC.00001: The source of holes in p-type In$_{x}$Ga$_{1-x}$N films Mary Ellen Zvanut, William Willoughby InGaN is an important alloy for many optoelectronic applications due to its tunable bandgap, which can range from $\sim $1-3 eV, corresponding to wavelengths of $\sim $400-1200 nm. In$_{x}$Ga$_{1-x}$N films, with x between 0.02 and 0.11, are studied at 4 K using electron paramagnetic resonance (EPR) spectroscopy. The films were made p-type by doping with Mg to a concentration of 2-3$\times $10$^{19}$ cm$^{-3}$, and the thickness of each film was between 0.25 and 0.44 $\mu $m. Hall measurements show that the hole density of a film increases with increasing In mole fraction, as expected, but the measured EPR intensity of the Mg-related signal is found to decrease. This trend is opposite of what is observed in other nitrides. Because the Mg-related EPR signal intensity represents the amount of unionized Mg, the amount of EPR detected Mg at low temperatures ($\sim $4K) tracks the hole concentration at room temperature in p-type GaN films. Together, compensating defects and a lowering of the acceptor level may explain the decrease in EPR intensity and the increase in hole density observed as the In mole fraction is increased. [Preview Abstract] |
Thursday, November 15, 2012 10:57AM - 11:09AM |
CC.00002: Non linear quantum decoherence behavior in the molecular magnet V15 Sylvain Bertaina, J. Shim, S. Gambarelli, T. Mitra, B. Tsukerblat, A. Muller, E. Baibekov, B. Malkin, B. Barbara Molecular magnets attract a great interest for many years since their potential application in quantum information processing. Quantum coherence, the property needed to create a qubit (fundamental piece of a quantum computer) has shown recently in V15 [1]. Since, the studies of decoherence behavior in molecular magnets have been extremely active. In the present talk, we will present a non linear microwave power dependence of the decoherence in V15 [2]. Generally, the decoherence probed but electron spin resonance increase linearly when the microwave field increase. Here we will show how the nuclear spin bath could dramatically change this dynamic. When the Rabi frequency is close to the nuclear Zeeman frequency coherence form the electron spin in transferred to the nuclear spin and is dissipated reducing the macroscopic electron spin coherence.\\[4pt] [1] Bertaina, S., Gambarelli, S., Mitra, T., Tsukerblat, B., M\"{u}ller, A., {\&} Barbara, B. (2008). Quantum oscillations in a molecular magnet. Nature, 453(7192), 203--6.\\[0pt] [2] Shim, J., Bertaina, S., Gambarelli, S., Mitra, T., M\"{u}ller, a., Baibekov, E., Malkin, B., et al. (2012). Decoherence Window and Electron-Nuclear Cross Relaxation in the Molecular Magnet V15. Physical Review Letters, 109(5), 1--5. [Preview Abstract] |
Thursday, November 15, 2012 11:09AM - 11:21AM |
CC.00003: Construction of a THz-Time Domain Spectrometer in Reflection Geometry Luke McClintock, Jeremy Curtis, David J. Hilton We have constructed a terahertz (THz) time-domain spectrometer in reflection geometry. THz time-domain spectroscopy (TTDS) is an ultrafast sampling technique that utilizes nonlinear optics to generate and detect the electric field reflected THz radiation. This unique sampling technique allows us to probe dynamics of materials that have absorption features in the THz frequency range at picosecond time scales. We have demonstrated the determination of optical constants of gallium arsenide using this spectrometer in the reflection geometry, which shows that this design overcomes many of the experimental difficulties traditionally associated with coherent terahertz measurements in the reflection geometry. [Preview Abstract] |
Thursday, November 15, 2012 11:21AM - 11:33AM |
CC.00004: Inductive Critical Currents in Nb/Ni bilayers Phillip Broussard, Emily Davis, Tim Ahrenholz We have carried out measurements of inductive critical currents in Nb/Ni bilayers. The films were grown by magnetron sputtering onto room temperature silicon substrates from separate sources. The bilayers were composed of an initial 33 nm Nb layer followed by a Ni layer, which was varied from 0-7 nm. Inductive critical currents were measured using a third harmonic technique at 1 kHz. $J_{c}$ varies as $(1-t)^{\gamma}$ with $\gamma$ being 3/2 as expected for pure Nb films, but decreasing as the Ni layer is increased (here $t$ is the reduced temperature, $T/T_{c}$). Our pure Nb film had a $T_{c}$ of 7.7 K with an inferred $J_{c}(0)$ of 61 MA/cm$^{2}$. As the Ni layer is increased, we see a marked reduction in the critical current which continues as the Ni layer is increased. Unlike the $T_{c}$'s for these samples, we do not see nonmonotonic behavior in the critical current, with $J_{c}(0)$ reducing to a constant value as Ni thickness goes beyond 3 nm. [Preview Abstract] |
Thursday, November 15, 2012 11:33AM - 11:45AM |
CC.00005: Tunable bands in biased multilayer epitaxial graphene Michael D. Williams, Duminda K. Samarakoon, Dennis W. Hess, Xiao-Qian Wang We have studied the electronic characteristics of multilayer epitaxial graphene under an electric bias. Ultraviolet photoemission spectroscopy measurements reveal that there is a notable increase of the electronic density-of-states in valence bands near the Fermi level. The evolution of electronic structure of rotational-stacked multilayer epitaxial graphene as a function of the applied electric bias is investigated using first-principles density-functional theory including interlayer van der Waals interactions. The tailoring of electronic band structure is shown to correlate with the interlayer coupling tuned by the applied bias. The implications of tunable electronic structure of rotational-stacked epitaxial graphene grown on the C-face of SiC for future device applications are discussed. Nanoscale DOI:10.1039/c2nr1199a [Preview Abstract] |
Thursday, November 15, 2012 11:45AM - 11:57AM |
CC.00006: Free flux flow: irradiation-induced effects and restricted geometries O. Gafarov, J.A. Alexander, A.A. Gapud, D.K. Christen, J.Z. Wu The field-dependent core size of magnetic flux quanta -- fluxons -- in the mixed state of Type II superconductors has a distinctive effect on free flux flow (FFF), the dissipative motion of fluxons in the absence of pinning. These core size effects have been previously observed by confirming a modification to the traditional Bardeen-Stephen flux-flow (BSFF) model by Kogan and Zelezhina (KZ) using high-density transport currents in weak-pinning, isotropic, low-$T_{c}$ compounds. Further exploration to provide insight into these phenomena are proposed: (1) Irradiation-induced effects on carrier scattering: FFF is affected by the electronic structure of the normal flux-core states; there is interest in how the flux dynamics could be altered by the modification of core states using low-level irradiation as a tool for incremental control of carrier scattering. (2) Restricted-geometry flux flow: Simulations of granular flow via FFF had been proposed previously; specifically, there is interest in observing the dynamics of flux flow through a narrow channel that has a two-dimensional ``hopper'' geometry, for comparison with known results from granular-flow studies. [Preview Abstract] |
Thursday, November 15, 2012 11:57AM - 12:09PM |
CC.00007: Alkanethiol Coated Nanosprings for the Detection of Nitrogen-Rich Explosives Jessica Hall, Alexander Larin, Dewayne Sowell, Vladimir Dobrokhotov In battle fields without clearly drawn lines such as Iraq and Afghanistan the detection of Improvised Explosive Device (IED) requires the use of advanced detection methods. A method of detection is to use alkanethiol coated nanosprings for the detection of nitrogen-rich explosives. The intent was to functionalize the nanospring mats for the detection of TNT, but through experimentation it was found that they are significantly more sensitive and selective to ammonium nitrate. Ammonium nitrate is the explosive component of fertilizer found in many IEDs. There is potential to incorporate these functionalized nanospring mats into an integrated system for the detection of IEDs. [Preview Abstract] |
Thursday, November 15, 2012 12:09PM - 12:21PM |
CC.00008: Morphology and conductivity studies on carbazole based GUMBOS thin films Kalyan Kanakamedala, Noureen Siraj, Madhavi Divakar, Farhana Hasan, Susmita Das, Isiah Warner, Theda Daniels-Race The use of thin films in opto-electronic devices such as organic light emitting diodes (OLEDs) and solar cells has been widely investigated. Historically with respect to the latter, multiple methods have been under study to improve device efficiency, yet the cost of production to meet general-purpose applications is still high. Addressing this challenge, we investigate the feasibility of carbazole based thin films as may be applied to future solar cell production. Based upon the recently discovered Group of Uniform Materials Based on Organic Salts (GUMBOS) [1], carbazole based GUMBOS and their nanoparticles were used in the preparation of thin films involving various techniques such as drop casting, vacuum drying, electrospraying and electrospinning. Via comparative studies of morphology and conductivity, we present results indicative of the potential opto-electronic functionality of these unique materials. \\[4pt] [1] A. Tesfai, B. El-Zahab, D.K. Bwambok, G.A. Baker, S.O. Fakayode, M. Lowry, I.M. Warner, Controllable formation of ionic liquid micro- and nanoparticles via a melt-emulsion-quench approach, Nano Letters, 8 (2008) 897-901. [Preview Abstract] |
Thursday, November 15, 2012 12:21PM - 12:33PM |
CC.00009: Adhesion measurement of carbon nanotube films deposited on silicon substrates Anirban Sarkar, Theda Daniels-Race Electrophoretic deposition (EPD) has attracted substantial interest as a room temperature based economical and versatile processing technique. EPD has been used in the fabrication of thin and thick films of carbon nanotubes (CNTs) on conducting substrates. However, in this work, to the best of our knowledge, for the first time EPD of CNTs on semiconducting substrates---both bare and coated (Si/SiO$_{2}$, Si/Si$_{3}$N$_{4})$ silicon --- has been investigated in detail. The process resulted in CNT film thicknesses of up to $\sim $15 $\mu $m from aqueous suspensions at low deposition voltages (5-30 V). A thin layer of metal film ($\sim $300 nm of aluminum), thermally evaporated on the samples, promotes adhesion between the CNTs in the EPD suspension and the intended target surfaces. In this study, post-EPD measurements have been investigated to assess the adhesion strength of the fabricated films. The qualitative measurements include the Peel Test (as per the American Society for Testing and Materials (ASTM) D-3359-97 standard) and ultrasonication tests. Direct pull off and nitrogen gas impingement tests have been developed for quantitative estimation. Experimental results indicate interfacial adhesion strength greater than 0.5-1 MPa between the fabricated films and substrates. Values reported are indicative of the applicability of electrophoretically fabricated CNT films for silicon based micro-electronics and MEMS development. [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