Bulletin of the American Physical Society
2018 Joint Spring Meeting of the Texas Sections of APS, AAPT, and Zone 13 of the SPS
Volume 63, Number 8
Thursday–Saturday, March 22–24, 2018; Stephenville, Texas
Session C6: APS III - Condensed Matter & Nano Science |
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Chair: Bimal Pandey, Tarleton State University Room: Science 102 |
Friday, March 23, 2018 2:30PM - 2:42PM |
C6.00001: Stability prediction and electronic properties study of silicon-rich silicon carbide Noura Alkhaldi, Muhammad N. Huda Silicon-rich silicon carbide structures which are thermodynamically stable can be used in applications without requiring a pure grade of Silicon or pure grade of silicon carbide materials. Density functional theory (DFT) calculations were used to examine the stability of various structures of silicon carbide in order to produce stable structures of silicon-rich silicon carbide materials. Since we found that changing the configuration of carbon atoms which are replaced by silicon atoms play a significant role in getting stable structures as well as lower band gaps, we investigated different configurations of silicon and carbon atoms in these silicon carbide structures to obtain suitable silicon-rich silicon carbide materials with tailored band gaps. We have studied the electronic structures of these structures as well. [Preview Abstract] |
Friday, March 23, 2018 2:42PM - 2:54PM |
C6.00002: Dual Beam MOKE Detection to Suppress the Effect Of Modulated Interference Effects In PEM Shankar Acharya, Brian Collier, Abdul Ahad Talukder, Wilhelmus Geerts The Magneto-Optical measurement method is often used to measure the magnetic hysteresis of thin films and multilayers. The method is more sensitive than vibrating sample magnetometry and allows for remote measurements. A Photo elastic modulator (PEM) is used to enhance the S/N ratio. The sample's magnetic moment is proportional to the 2f intensity signal. Strong coherent noise at the modulator oscillation's frequency and its harmonics arises due to interference between the primary laser beam and beams that undergo multiple reflections in the PEM's optic head. In dual beam MOKE detection, the beam transmitted through the sample is split in two high quality linearly polarized beams by a Wollaston Prism. The intensity of the beams is measured by two Si detectors employing lock-in amplifiers. Optics and detectors are mounted in an optical rotation stage allowing for them to be rotated together around the setup's optical axis. A PC running Labview was used to control the PEM angle, the magnetic field, and the Polarizer and Analyzer angles. Above-mentioned coherent noise can be largely reduced by subtracting the 2f components of both transmitted beams [1]. [1] Md. Abdul Ahad Talukder, Wilhelmus J. Geerts, AIP Advances 7, 085320 (2017). [Preview Abstract] |
Friday, March 23, 2018 2:54PM - 3:06PM |
C6.00003: Several Approaches to Realistic Dynamical Simulations in Advanced Materials Michael Tagaras, Jian Weng, Roland Allen This talk will cover several methods for realistic dynamical simulations of advanced materials, including ultrafast phase transitions. In our first method, Ginzburg-Landau-like order parameters are coupled to one another and to the vector potential of an incoming laser pulse, so that the resulting phase transition is described by time-dependent Ginzburg-Landau theory. This approach is capable of describing one mechanism which is observed in light-induced superconductivity. Secondly, a new method will be introduced for treating ultrafast phase transitions, such as those involving superconductivity, magnetism, charge density waves, and spin density waves. Illustrative results will be presented for a toy model, with the electronic temperature immediately after the laser pulse calculated as a function of the fluence. Finally, we modify this approach with the addition of an electronic self-energy, which allows for calculations currently not possible with conventional density-functional-based methods. [Preview Abstract] |
Friday, March 23, 2018 3:06PM - 3:18PM |
C6.00004: Low-energy electron irradiation on multi-layers graphene John Femi-Oyetoro, Runtian Tang, Ashley Mhlanga, Phillip Ecton, Guido Verbeck, Jose Perez We performed low-energy (about 60 eV) electron irradiation experiments on exfoliated samples from highly-oriented-pyrolytic graphite onto 300nm thick SiO$_{\mathrm{2\thinspace }}$/Si substrates, using a plasma system. After irradiation, the few-layers disappeared and intermediate thickness regions appeared lighter. Optical contrast microscopy and atomic force microscopy images taken before and after irradiation, show that the surface of the multi-layers appears rough with etch features. This experiment ascertains that etching is not from the oxygen dissociated from the graphene/SiO$_{\mathrm{2}}$ interface due to secondary electrons in the graphene. Our observations indicate that etching proceeds from the top surface of the multi-layer graphene downwards instead of upwards from the graphene/SiO$_{\mathrm{2}}$ interface. We observed similar results with samples that were pre-annealed at 400\textdegree C at about 5 \texttimes 10$^{\mathrm{-6}}$ Torr for 1hr. to remove adsorbates. We conclude that the etching observed is due to oxygen dissociated from bare SiO$_{\mathrm{2}}$ regions of the substrate instead of SiO$_{\mathrm{2}}$ at the graphene/SiO$_{\mathrm{2}}$ interface. [Preview Abstract] |
Friday, March 23, 2018 3:18PM - 3:30PM |
C6.00005: Photocurrent improvisation of BiVO$_{\mathrm{4}}$ photocatalyst by electronic structure engineering via Nb doping Hori Pada Sarker, Muhammad N Huda Monoclinic BiVO$_{\mathrm{4}}$ has been said to achieve one of the highest hydrogen production efficiency. Although BiVO$_{\mathrm{4\thinspace }}$is a good sunlight absorber, the transport of photo generated charge carriers is complex. The electron-hole recombination is a major barrier to achieve higher photo-current in BiVO$_{\mathrm{4}}$. The conduction band minima of BiVO$_{\mathrm{4}}$ is composed of V 3d localized band which contributes to higher resistivity of the photo generated charge carriers. In this present study, density functional theory (DFT) has been used to study Nb incorporation in BiVO$_{\mathrm{4}}$ to see the electronic structure changes. It was found that Nb incorporation in BiVO$_{\mathrm{4}}$ changes the conduction band minima and V 3d band is replaced by less localized Nb 4d bands. It was also found that it may create shallow donor level. Less localized Nb 4d band in conduction band minima and donor level in the band structure will facilitate the charge carrier transport and hence improve the photocurrent of BiVO$_{\mathrm{4}}$. The solubility of Nb within BiVO$_{\mathrm{4}}$ has been studied. In addition, via chemical potential landscape analysis, the single-phase stability zone of BiVO$_{\mathrm{4}}$ with Nb will be presented. [Preview Abstract] |
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