Bulletin of the American Physical Society
2011 Fall Meeting of the APS Ohio-Region Section
Volume 56, Number 8
Friday–Saturday, October 14–15, 2011; Muncie, Indiana
Session ED: Condensed Matter Physics II |
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Chair: Mohammed Saiful Islam, Ball State University Room: Cooper Science CP92 |
Saturday, October 15, 2011 8:30AM - 8:45AM |
ED.00001: Fabrication of All-Inorganic Nanocrystal Solids through Matrix Encapsulation of Nanocrystal Arrays Dan Roth, Erich Kinder, Pavel Moroz, Geoffrey Diederich, Alexa Johnson, Maria Kirsanova, Alexander Nemchinov, Timothy O'Connor, Mikhail Zamkov A general strategy for low-temperature processing of colloidal nanocrystals into all-inorganic films is reported. The present methodology goes beyond the traditional ligand-interlinking scheme and relies on encapsulation of morphologically-defined nanocrystal arrays into a matrix of a wide-band gap semiconductor, which preserves optoelectronic properties of individual nanoparticles while rendering the nanocrystal film photoconductive. Fabricated solids exhibit excellent thermal stability, which is attributed to the heteroepitaxial structure of nanocrystal-matrix interfaces, and show compelling light-harvesting performance in prototype solar cells. [Preview Abstract] |
Saturday, October 15, 2011 8:45AM - 9:00AM |
ED.00002: The Role of Hole Localization in Sacrificial Hydrogen Production by Semiconductor-Metal Heterostructured Nanocrystals Scott Lambright, Krishna P. Acharya, Rony S. Khnayzer, Timothy O'Connor, Geoffrey Diederich, Maria Kirsanova, Anna Klinkova, Daniel Roth, Erich Kinder, Martene Imboden, Mikhail Zamkov The effect of hole localization on photocatalytic activity of Pt-tipped semiconductor nanocrystals is investigated. By tuning the energy balance at the semiconductor-ligand interface, we demonstrate that hydrogen production on Pt sites is efficient only when electron-donating molecules are used for stabilizing semiconductor surfaces. These surfactants play an important role in enabling an efficient and stable reduction of water by heterostructured nanocrystals as they fill vacancies in the valence band of the semiconductor domain, preventing its degradation. In particular, we show that the energy of oxidizing holes can be efficiently transferred to a ligand molecule, leaving the semiconductor domain intact. This allows re-using the inorganic portion of the ``degraded'' nanocrystal-ligand system simply by recharging these nanoparticles with fresh ligands. [Preview Abstract] |
Saturday, October 15, 2011 9:00AM - 9:15AM |
ED.00003: Cathodoluminescence Study of Hafnium Oxide Emily Purcell, Robert Hengehold, John McClory Hafnium dioxide (HfO2) is increasingly being used in place of silicon oxide as a gate insulator in field effect transistors. This is primarily due to its high dielectric constant, $\kappa $, of 25. Samples of HfO$_{2}$ were grown by either atomic layer deposition (ALD) or pulsed laser deposition (PLD), with the PLD samples having assorted substrate temperatures during deposition (300\r{ }C, 500\r{ }C, and 750\r{ }C). Cathodoluminescence (CL) was chosen as the technique used for studying these HfO$_{2}$ samples. The CL system used was capable of beam energies ranging from 1 keV to 20 keV and beam currents ranging from 10 $\mu $A to 50 $\mu $A. A Monte Carlo calculation using CASINO software was performed in order to determine the beam energy for the desired depth of penetration. Measurements were taken at sample temperatures ranging from 7K (closed cycled cryostat) to 300K (room temperature), as well as at various beam energies and beam currents. Comparison will be made between the PLD and ALD spectra. [Preview Abstract] |
Saturday, October 15, 2011 9:15AM - 9:30AM |
ED.00004: Measurements of Resonant Activation and Multiple Gap Structure in MgB2 Thin Film Josephson Junctions near 1 Kelvin Roberto Ramos, Steven Carabello, Joseph Lambert, Jerome Mlack, Daniel Cunnane, Wenqing Dai, C.G. Zhuang, Yi Shen, Ke Chen, Qi Li, X.X. Xi Superconductivity in magnesium diboride (MgB2) is of great practical interest because of its high superconducting transition temperature Tc of 39K and its relatively low cost and relative ease of manufacturing. We report the results of two experiments investigating MgB2-based thin film Josephson junctions fabricated by hybrid physical-chemical vapor deposition (HPCVD). First, Josephson junctions behave like a nonlinear oscillator with a phase particle that can escape the Josephson potential either through thermal activation or quantum tunneling. We report results of our thermally- and microwave-assisted resonant activation experiments. We see evidence of a resonant peak, in addition to the primary escape peak, consistent with theoretical predictions. We have also conducted low-temperature tunneling spectroscopy studies of MgB2 that confirm substructure within both energy gaps of MgB2, in agreement with theoretical predictions. [Preview Abstract] |
Saturday, October 15, 2011 9:30AM - 9:45AM |
ED.00005: Canopy Dynamics in a Nanoscale Ionic Material E. von Meerwall, M.L. Jespersen, P.A. Mirau, R.A. Vaia, N.J. Fernandes, E.P. Giannelis We have used nuclear magnetic resonance (NMR) relaxation and pulsed-gradient diffusion measurements to characterize molecular mobility in a set of nanoscale ionic materials (NIMS). 18 nm core silica nanoparticles were functionalized with a covalently attached alkyl silane monolayer corona followed by an ionically tethered bulky ethylene oxide/propylene oxide block copolymer canopy. NIMS are organic-inorganic hybrids exhibiting liquid-like character under ambient conditions in the absence of solvent and are of interest for a variety of applications. Our NMR studies show that the fast (ns) local dynamics of the block copolymer canopy are insensitive to the presence of the silica nanoparticles. Canopy diffusion in the NIMS is only modestly slowed relative to the neat copolymer. Not all canopy molecules are slowed equally due to crowding at the corona-coated nanoparticle surface, resulting in strongly bound fraction at the surface and weakly bound outer sphere capable of rapid exchange of canopy molecules between host particles. Electrostatic interactions with other ionic (Na$^{+})$ species alter the dynamics by decreasing the strongly-bound population. [Preview Abstract] |
Saturday, October 15, 2011 9:45AM - 10:00AM |
ED.00006: Partial Kerma Factors for Neutron Scattering from ${ }^{16}O^{ }$ Mohammed Islam Success for the use of neutron for radiation therapy and other applications in radiological physics depends on the understanding of the interaction of neutron with elements in the tissue. Study of the mechanisms of energy deposition by neutron interaction with matter is very important to improve the understanding of the neutron dosimetry. Cross section data are the basic inputs for many types of calculations in radiation physics. One important quantity in some radiological applications of neutron is the kerma (kinetic energy released in material.) Differential elastic and inelastic neutron scattering from some elements of biological interests are available at energies 18 -- 26 MeV. Optical Model Potentials based on these measured cross sections may be used to calculate various quantities of interest for the neutron dosimetry at higher energies where cross section data may not be available. Kerma values for elastic and inelastic scattering of neutron from $^{16}$O are obtained from differential cross sections. [Preview Abstract] |
Saturday, October 15, 2011 10:00AM - 10:15AM |
ED.00007: Superconducting Quantum Interference Filters as Detectors of AC Magnetic Fields Christopher Porter A theoretical study is presented of the voltage responses of 1-D arrays of N Josephson junctions to AC and DC magnetic fields. Numerical results are shown for various values of parameters such as the number of junctions N, the relative strengths of the AC and DC magnetic fields, and the frequency of the incoming AC field. An analytical description of the smearing effect of AC fields on the voltage signal is also discussed in some parameter regimes. Detection of small-amplitude AC fields using both uniform and non-uniform junction spacing is demonstrated. Considerable difficulty in determining large-amplitude AC fields highlights the need for a voltage response that is monotonic in flux for AC signal detection. Non-uniform spacing is examined to eliminate the voltage signal's $\Phi _0 $-periodicity in flux, allowing Josephson arrays to function as absolute detectors of AC (and DC) magnetic field. Various junction spacing schemes are considered in an effort to optimize the voltage signal produced by the array for the detection of AC magnetic fields. Extremely long periods are achieved, but a monotonic voltage response remains elusive. [Preview Abstract] |
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