Bulletin of the American Physical Society
2016 Fall Meeting of the APS Ohio-Region Section
Volume 61, Number 12
Friday–Saturday, October 7–8, 2016; Bowling Green, Ohio
Session C2: Condensed Matter Physics and Materials Research I |
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Chair: Katalia Khomicheva, Bowling Green State University Room: 308 |
Saturday, October 8, 2016 9:30AM - 9:42AM |
C2.00001: Universe of constant Han Yongquan Ideal gas equation of state is not applicable to ordinary gas, it should be applied to the Electromagnetic "gas" that is applied to the radiation, the radiation should be the ultimate state of matter changes or start state, the universe is filled with radiation. That is, the ideal gas equation of state is suitable for the Singular point and the universe. Maybe someone said, no vessel can accommodate radiation, it is because t Ordinary container is too small, if the radius of your container is Light an hour through the distance y You must say, can accommodates radiation. Modern scientific determination of the radius of the universe is about now: 10$^{\mathrm{27}}$ m, assuming that the universe is a sphere whose volume is approximately: V $=$ 4.19 × 10$^{\mathrm{81}}$ cubic meters, temperature radiation (cosmic microwave background radiation temperature of the universe, the universe should be the closest the average temperature) T $=$ 3.15k, radiation pressure P $=$ 5 × 10$^{\mathrm{-6\thinspace }}$N / m $^{\mathrm{2}}$, according to the ideal gas equation of state law, PV / T $=$ constant $=$ 6 × 10$^{\mathrm{75}}$, the value of this constant is the universe, constant of The singular point is equal to the constant Author: hanyongquan [Preview Abstract] |
Saturday, October 8, 2016 9:42AM - 9:54AM |
C2.00002: Characterizing the Swelling of a Crosslinked Organosilicon Polymer Zane Thornburg, Paul Bonvallet A hydrophobic crosslinked organosilicon polymer, known by the trade name Osorb, absorbs many times its own weight in liquid- and vapor-phase organic solvents. Its Si---O---Si linkage is likely flexible, analogously to physical and spectroscopic measurements in various forms of silica. Infrared spectroscopy is commonly used due to the sensitivity of certain vibrational modes to changes in geometry and environment. We hypothesized that the Si---O---Si bond angle within the Osorb matrix changes when the material swells upon exposure to organic solvents. Density functional theory calculations on a small-molecule model system qualitatively agree with the central force model of glassy solids, which relates the IR vibrational frequency of the system to the angle and force constant of this bond. Treatment of various Osorb samples with decane consistently causes a moderate increase in the frequency of the asymmetric stretching band around 1100 cm$^{\mathrm{-1}}$. However, the spectroscopic changes do not correlate with the swell capacity of the material. In fact, some low-swelling samples showed the same changes in frequency as high-swelling samples, thus demonstrating that the swelling of Osorb is not due to changes in the Si---O---Si bond angle. [Preview Abstract] |
Saturday, October 8, 2016 9:54AM - 10:06AM |
C2.00003: Polymer folding in confined and crowded environments Mark Taylor, Christopher Vinci A single polymer chain can undergo a series of conformational transitions analogous to the phase transitions exhibited by bulk materials. We have recently studied the conformational transitions of a flexible square-well polymer chain using a Wang-Landau simulation approach in which we directly compute the single-chain partition function [1]. For the case of a tangent-sphere chain, a sufficiently short-range interaction gives a direct coil-crystal transition analogous to the all-or-none folding transition exhibited by fast-folding proteins. Here we investigate the effects of geometric confinement on this folding transition. One anticipates that confinement will reduce the entropy of the unfolded chain, thereby stabilizing the folded state and shifting the transition to higher temperature. Here we study the folding transition of a flexible square-well N-mer chain (monomer diameter d) that is (A) located between two hard walls forming a slit-like pore with the chain end-tethered to one wall and (B) immersed in a hard-sphere solvent with solvent diameter D $>$= d and solvent volume fraction 0 $<$ vf $<$ 0.4. An entropic stabilization effect is found in both cases. [1] Taylor, Paul, and Binder, J. Chem. Phys. 131, 114907 (2009) [Preview Abstract] |
Saturday, October 8, 2016 10:06AM - 10:18AM |
C2.00004: The Electronic Properties of Hexagonal Boron Nitride and Graphene Nanoribbons Albert DiBenedetto, Mahfuza Khatun, Antonio Cancio Energy storage and device fabrication is an area of condensed matter physics that's widely studied by utilizing extremely tiny, two-dimensional nanostructures like hexagonal boron nitride nanoribbons (BNNRs) and graphene nanoribbons (GNRs). We are investigating the electronic properties of both materials. Results of band structure, density of states (DOS), and conductance of both materials will be presented. In addition, effects of impurities that alter their electronic behavior will be discussed. The BNNRs are insulating and on the other hand, GNRs are either metallic or semiconducting. Theories include a Tight-Binding (TB) model with Huckel theory, equilibrium Green's function method, Landauer formalism, and Density Functional Theory (DFT). The TB model is used to calculate the band structures and DOS, and the Green's function theory and Landauer formula are used to obtain the transmission function and the conductance. ABINIT computational software implements DFT to calculate the band structure of boron nitride and VMD software is used to visualize the electron density. The results of DFT will be compared with the TB model. [Preview Abstract] |
Saturday, October 8, 2016 10:18AM - 10:30AM |
C2.00005: Monitoring Charge Separation and Injection Processes of Semiconductor Perovskite Thin Films Christopher McCleese, Lili Wang, Yixin Zhao, Clemens Burda In the past several years, semiconductor perovskites have had a major impact on the field of photovoltaics with device efficiencies reaching up to 20.1{\%}. By studying the photophysical properties of these sensitizers, valuable information about the charge carrier relaxation processes is gained and insight into charge transfer and recombination processes that occur within the sensitizer and its interfaces after photoexcitation is obtained, all of which are useful to further help increase the efficiencies of perovskite based devices. Two of the main variables that have shown to have an effect on device efficiency is the substrate that the perovskite is coated on and the precursors used to prepare the perovskite films. In this talk I will focus on the ultrafast photophysics of perovskites studied by way of time resolved photoluminescence measurements. To better understand how the aforementioned variables effect device efficiencies, the ratio of CH$_{3}$NH$_{3}$I:CH$_{3}$NH$_{3}$Cl:PbI$_{2}$ in the precursor solution is varied and these solutions are coated on either a planar or mesoporous TiO$_{2}$ substrate. The charge carrier injection dynamics of these prepared films are investigated and their implications on device efficiencies is discussed. [Preview Abstract] |
Saturday, October 8, 2016 10:30AM - 10:42AM |
C2.00006: Role of symmetries on the indirect interaction between magnetic moments in triangular MoS$_{2}$ nanoflakes Oscar Avalos-Ovando, Diego Mastrogiuseppe, Sergio Ulloa We study the Ruderman-Kittel-Kasuya-Yosida interaction between magnetic impurities embedded in transition-metal dichalcogenide triangular flakes, via a 3-orbital tight binding model. We consider impurities hybridized to transition-metal sites and also at interstitial points. We find that the interaction is drastically different well inside of the flake and near the edges. The strong spin-orbit interaction in these materials produces an effective Dzyaloshinskii-Moriya exchange interaction that can be sizable and tunable, by taking advantage of the symmetry of the system. The interaction is anisotropic for impurities in the interior of the flake. However, when impurities lie near the edges of the flake, the effective exchange is Ising-like, associated with the presence of $d_{z^2}$-orbitals dominant at edge states. Other tunable interactions are possible by selecting impurity positions and orbital character of the states in their neighborhood. Our results could provide new ways for controlling the helical long-range order in magnetic atom arrays, including 1D chains. [Preview Abstract] |
Saturday, October 8, 2016 10:42AM - 10:54AM |
C2.00007: Valley polarization in graphene via out-of-plane deformations Dawei Zhai, Nancy Sandler The low energy dispersion of graphene shows a conical valley structure with the conduction and valence bands touching at the Dirac points. The existence of two inequivalent Dirac points, thus two valleys, suggests that they may be used as new degrees of freedom to carry information. However, existing proposals based on different mechanisms for achieving valley separation in graphene remain challenging for experimental verification. In this work we investigate graphene with out-of-plane deformations- one of the most naturally occurring and practically realizable settings, as a candidate system to produce valley polarization. Specifically, we consider local Gaussian bumps and extended Gaussian folds. In the first case, the corresponding local strains serve as scattering potentials for electronic states. A second-order Born approximation calculation based on the continuum model reveals the existence of valley polarization. While in the second case, the strains serve as magnetic barriers, which has distinct impacts on the transmission of electrons from different valleys. The valley polarization shows dependence on the geometrical parameters of the deformations in both cases. The efficiency of valley polarization for different geometries and energies will be discussed. [Preview Abstract] |
Saturday, October 8, 2016 10:54AM - 11:06AM |
C2.00008: Origins of Luminescence and Scintillation in Un -- Doped Single Crystal Zinc Oxide A. M. Colosimo, J. Ji, P. S. Stepanov, W. Anwand, A. Wagner, L. A. Boatner, F. A. Selim The origins of the luminescence and scintillation properties of zinc oxide are studied by means of photo -- luminescence (PL), X -- ray induced luminescence (XRIL) [Review of Scientific Instruments 83, 103112(2012)], gamma -- induced positron spectroscopy (GIPS), and scintillation counting measurements such as coupling the ZnO crystals to a photomultiplier tube (PMT) to measure rise times and collect spectra. The ultra-violet and green emissions in single crystal ZnO are probed by X -- ray excitation, and XRIL data exhibits an excellent linear relationship between the increase in the ZnO emission intensity and the increase in X -- ray tube current. Rise times and scintillation counting spectra were measured from the anode and dynode signals of the PMT, respectively, with sub -- nanosecond rise times acquired. This combination of the scintillation counting and XRIL measurements revealed a strong correlation between the fast scintillation in the single crystal ZnO and the ratio between the defect luminescence (DL) and near band emission (NBE). GIPS is a sensitive method of measuring cation vacancies in semiconductors, and the unique defect spectroscopy method enables collection of positron lifetime decay curves for the ZnO samples, free of background and source contributions. [Preview Abstract] |
Saturday, October 8, 2016 11:06AM - 11:18AM |
C2.00009: Measuring Thermal Processes of Methylammonium Lead Iodide (CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbI$_{\mathrm{3}})$ Perovskite Anton Kovalsky, Lili Wang, Gage Marek, Xin Guo, Clemens Burda, Jeffrey Dyck Perovskites have~recently been the focus of much research due to their performance as a photosensitizers for solar energy conversion applications. We have explored the thermal properties of this material, focusing on the role~of the cation methylammonium within the perovskite lattice.~Temperature-dependent thermal conductivity of the perovskite in~the range between 7K and 300K was compared to the cesium perovskite analog, and the data were~fitted to a Debye model, revealing the effect of the methylammonium component on~phonon scattering and a source of increased thermal resistance. Thermal conductivity was also measured for naturally aged perovskite samples,~showing that the degradation product's thermal behavior approaches that of lead iodide, one of~the thermodynamic end products. Our results~highlight the effectiveness of thermal transport measurements for analyzing material integrity of perovskite-based devices. [Preview Abstract] |
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