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 E2: Condensed Matter Physics and Materials Research II |
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Chair: Natalia kholmicheva, Bowling Green State University Room: 308 |
Saturday, October 8, 2016 1:30PM - 1:42PM |
E2.00001: Coarse-grained model for oligothiophenes in the bulk and near surfaces Jutta Luettmer-Strathmann, Amani Almutairi The interfacial layer of an organic semiconductor in contact with a metal electrode has important effects on the performance of thin-film devices. However, the structure of this layer is not easy to model. Oligothiophenes are small, conjugated molecules with applications in organic electronics that also serve as small-molecule models for polythiophenes. Hexithiophene (6T) is a six-ring molecule, whose adsorption on noble metal surfaces has been studied extensively (see, e.g., Ref. [1]). In this work, we develop a coarse-grained model for oligothiophenes. We describe the molecules as linear chains of bonded, discotic particles with Gay-Berne potential interactions between non-bonded ellipsoids. We perform Monte Carlo simulations to study the structure of oligothiophenes in the bulk and near surfaces. [1] M. Kiel et al. Phys. Rev. B 75, 195439 (2007). [Preview Abstract] |
Saturday, October 8, 2016 1:42PM - 1:54PM |
E2.00002: Optoelectronic Characterization and Luminescence Studies of Sn doped ZnO Single Crystals Micah Haseman High quality undoped and Sn doped zinc oxide (Sn:ZnO) single crystals were grown by the chemical vapor transport method (CVT) and the effects of Sn doping on the electrical and optical properties of ZnO were investigated. Sn doping led to a marked increase in the electrical conductivity, carrier concentration and Hall mobility. The increase in carrier concentration was associated with a change in color from colorless to dark blue. Optical absorption measurements revealed that the dark blue color is due to a broad peak in the red region and is unrelated to the optical band gaps of the crystals. We anticipate that the formation of defect complexes that quench the luminescence are induced by Sn doping while Sn donors are behind the increase in electrical conductivity and the deep coloration. Using low-temperature thermal stimulated luminescence spectroscopy, a number of donor species have been identified with donor ionization energies ranging from 35 to 118 meV. [Preview Abstract] |
Saturday, October 8, 2016 1:54PM - 2:06PM |
E2.00003: Circumventing Non Ergodic Dynamics in Anharmonic Atomic Chains Christopher Watenpool, Donald Priour Thermalization of chains in which atoms interact via a harmonic potential is precluded by the lack of interactions among normal modes, and is even hampered in anharmonic chains in the low temperature regime. Using molecular dynamics simulations (averaged over many runs to suppress noise), with Langevin Heat Baths applied at the ends, the energy exchange with the environment provides stochastic input, thereby facilitating equilibration while preserving the internal dynamics of the chain. We examine systems with a finite energy site stored in the lowest harmonic, as well as cold chains with zero energy per site. We use the ensemble averaged effective mode occupancy and effective temperature to calculate the time scale for equilibration. In the low temperature regime, we find the effective temperature (determined from the mean kinetic energy per site) to rise by a factor of two for chains with the fundamental excited before relaxing to the equilibrium value. Times for ensemble averaged mode occupancies to reach a threshold value are threshold independent and follow a smooth power law. For cold chains, relaxation times for the effective temperature are noisy with fluctuations among independent runs comparable to the mean value. [Preview Abstract] |
Saturday, October 8, 2016 2:06PM - 2:18PM |
E2.00004: Strain effects in the electronic structure of CrN Tomas Rojas Solorzano, Sergio E. Ulloa Chromium nitride (CrN) has a promising future for its resistance to corrosion and hardness, and fascinating magnetic and electronic properties. CrN presents a phase transition in which the crystal structure, magnetic ordering, and electronic properties change at a (Neel) temperature ~280K. Thin films from different labs exhibit different conductance behavior at low temperature. We performed ab initio calculations using the LSDA+U method, and estimate the interaction between the Cr-3d and N-2p orbitals, by analyzing the band structure. We also calculate effective masses and investigate the effect of strain fields in the electronic structure to understand the electronic behavior near the phase transition. [Preview Abstract] |
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