Bulletin of the American Physical Society
82nd Annual Meeting of the APS Southeastern Section
Volume 60, Number 18
Wednesday–Saturday, November 18–21, 2015; Mobile, Alabama
Session A2: Condensed Matter Physics I |
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Chair: Albert Gapud, University of South Alabama Room: Riverview Plaza Hotel Mobile Bay Ballroom I |
Thursday, November 19, 2015 8:30AM - 8:42AM |
A2.00001: Graphene Oxide Frameworks for Carbon Capture Applications Jacob Burress, Elizabeth Baker, Donald Bethea, Katherine Frangos Growing concerns about anthropogenic global warming have concentrated scientific efforts on the reduction of greenhouse gases. The reduction of a significant greenhouse gas, carbon dioxide (CO2), is paramount. Physical sorbents possess many benefits over alternative storage and capture methods, including reusability. This project investigates nanoporous, physical sorbent materials for the separation of carbon dioxide. Van der Waals adsorption of gases is exploited in the use of nanoporous (pore width ca. 1 nm) materials for the storage and separation of gases. The material presented is a relatively new class of materials called graphene oxide frameworks (GOFs). GOFs consist of layers of graphene kept separated by organic linkers, in this case boronic acids. These materials are of interest because of the customizability of the pore width and chemistry through the careful selection of a wide variety of linkers. Results on the carbon dioxide separation in these materials will be presented. Additionally, results from chemical and structural analysis of these materials will be shown. These materials exhibit pore breathing, e.g. pore geometry expansion with increased pressure. Analysis of this behavior will also be presented. [Preview Abstract] |
Thursday, November 19, 2015 8:42AM - 8:54AM |
A2.00002: First principles studies of the interaction between metal clusters and graphene RAISI BALDEZ, PAULO PIQUINI, ALEX SCHMIDT, MARCELO A KURODA Due to its outstanding electrical, mechanical, and thermal properties, graphene is a promising material for a wide range of applications. However, making electrical contacts to this two-dimensional system has been a challenging task. In this work we analyze the interaction of small metal clusters with pristine and defective graphene layers using first principles calculations. The lowest energy structures of free clusters of different metals (Au, Pd, Pt and Ti) were obtained using a genetic algorithm approach. We find that the adhesion of these metal clusters in defective graphene, even if away from the defects, is substantially larger than in pristine graphene. Among the metals considered in our study, Ti clusters form the strongest binding with pristine or defective graphene. The resulting band structures show a strong hybridization of the Ti/C orbitals, which explains the origin of the enhanced binding energies. [Preview Abstract] |
Thursday, November 19, 2015 8:54AM - 9:06AM |
A2.00003: Optical properties of plasmon-coupled charge carriers in CuInS$_{\mathrm{2}}$ and CuInS$_{\mathrm{2}}$/ZnS QDs Quinton Rice, Sangram Raut, Rahul Chib, Anderson Hayes, Zygmunt Gryczynski, Ignacy Gryczynski, Young-Kuk Kim, Bagher Tabibi, Jaetae Seo The optical properties of plasmon-coupled charge carriers in copper indium disulfide (CIS) and CIS/ZnS QDs were investigated by time-resolved and temperature-dependent photoluminescence (PL) spectroscopy. The fractional Purcell enhancement of plasmon-coupled charge carriers in CIS was observed at shorter, intermediate, and longer spectral regions. The PL lifetimes at surface-/interface-trapped states and shallow-defect states are relatively shorter than those at at deep-trapped states. The temperature-dependent PL studies revealed that the plasmon-exciton coupling reduces the PL thermal quenching, and the charges at surface-/interface-trapped states and shallow-defect states are thermally active compared to the charges at deep-trapped states. The reduction of non-radiative decays in addition to the strong local field leads to the large PL enhancement. The larger PL enhancement of plasmon-coupled CIS/ZnS in comparison with that of plasmon-coupled CIS is accredited to the significant defect-mediated Purcell enhancement for bright emission materials. The Purcell enhancement of plasmon-coupled QDs is attributable to the coupling between plasmon and defect-related carrier pairs through Coulomb interaction and the local field enhancement. [Preview Abstract] |
Thursday, November 19, 2015 9:06AM - 9:18AM |
A2.00004: Effects of $\gamma $-Al$_{\mathrm{\mathbf{2}}}$O$_{\mathrm{\mathbf{3}}}$ Support on the Morphology and Electronic Structure of Pt Nanoparticles Ghazal Shafai, Sampyo Hong, Talat S. Rahman We have studied the effects of pristine and hydroxylated $\gamma $-Al$_{\mathrm{2}}$O$_{\mathrm{3}}$(110) support on the morphology and electronic structure of clean and H-covered Pt nanoparticles (NP) containing 22 and 44 atoms (Pt$_{\mathrm{22\thinspace }}$and Pt$_{\mathrm{44}})$ using density functional theory (DFT) based calculations. We find a morphology change from 3 dimensional (3D) to a bi-planar shape for Pt$_{\mathrm{22}}$ upon adsorption on pristine and partially hydroxylated $\gamma $-Al$_{\mathrm{2}}$O$_{\mathrm{3}}$(110) surface. This shape change is not found for higher hydroxylation coverage (0.325 monolayer (ML) and higher) or for Pt$_{\mathrm{44}}$, indicating that the aforementioned effect is size and OH coverage dependent. Furthermore, the relative position of the d-band center of the unoccupied orbitals of the nanoparticles is sensitive to the presence of the support and the extent to which it is hydroxylated. A competing and even dominating effect on the electronic structure of the nanoparticles comes from adsorbed hydrogen. At higher temperatures when the effect of adsorbates is minimal, the shift in the d-band center of the unoccupied orbitals is found to correlate with the extent of metal-support interaction In the light of these results, we conclude that an accurate description of the local environment of nanoparticles (support, hydroxylation of the support, adsorbed hydrogen) is necessary in order to understand the preferred shape and electronic structure of these nanoparticles. [Preview Abstract] |
Thursday, November 19, 2015 9:18AM - 9:30AM |
A2.00005: Ion Transport in Macrocapillaries Luke Lyle, Dhruva Kulkarni, Chad Sosolik We present results on ion transport through large bore capillaries that probe both the geometric and ion-guided aspects of this ion delivery mechanism. The initial observation of ion transport by Stolterfoht [Stolterfoht et al. \textit{Physics Review Letters}, \textbf{88}, 13(2002)] through insulating capillaries has sparked interest in possible new, flexible ion beamline designs that would rely on a combination of charge patch formation and external electric field guiding. Implementing such designs will require studies of the underlying physical mechanisms for transport and guiding, both of which are materials-dependent. We demonstrate that guiding in macrocapillaries exhibits position- and angle-dependent transmission directly related to the capillary material and geometry. Specifically, we have passed 1 keV Rb$^{+\, }$ions through glass and metal macrocapillaries of varying diameter, and have observed oscillations for ion current passing through the insulating capillaries. Calculations show that these oscillations can be attributed to beam deflections from charge patches that form on the interior walls of the capillary. The absence of these oscillations in the metal capillary data serve as further confirmation of the role of charge patch formation. [Preview Abstract] |
Thursday, November 19, 2015 9:30AM - 9:42AM |
A2.00006: Can metal plate specimens deform after removal of tensile loads? Hiroshi Ono, Christopher Webster, Sanichiro Yoshida, Tomohiro Sasaki We conduct experimental studies on fatigue of metals using an optical interferometric technique called the Electronic Speckle-Pattern Interferometry. The ESPI setup is configured to measure the in-plane displacement parallel to the tensile axis. The displacement is evaluated via analysis of interferometric fringes generated by subtracting the interferometric image taken at a time step from that taken at the initial time step; each fringe represents a contour of constant displacement occurring during the interval between the two time steps. We apply a tensile load to thin-plate specimens at a constant pulling rate to a pre-set stress substantially lower than the yield stress. In the course of these experiments, we have noticed that after the tensile machine stops pulling the specimens, the fringe pattern exhibits deformation. To investigate this mysterious but intriguing phenomenon, we have conducted a series of experiments on an aluminum alloy (A7075) specimen using the same experimental setup where we keep the interferometer running after the tensile machine stops pulling. Consequently, we have found that the specimen indeed experience deformation 10 - 15 sec after the grip stops. [Preview Abstract] |
Thursday, November 19, 2015 9:42AM - 9:54AM |
A2.00007: Positive Upper Critical Field Curvature in Niobium Thin Films: Dependence on Purity Phillip Broussard, Angela Hunziker Thin films of niobium deposited by magnetron sputtering have been characterized by critical field measurements with the magnetic field applied perpendicular to the film plane. Film thickness varied from 16 to 100 nm, and using various deposition conditions, the parameter $\lambda_{\mathrm{tr}}=0.882 \xi_{0}/\ell_{\mathrm{tr}}$ (where $\xi_{0}$ is the BCS coherence length and $\ell_{\mathrm{tr}}$ is the elastic mean free path) varied from 2 to 14. Even films that are considered in the ``dirty'' limit ($\lambda_{\mathrm{tr}}>>1$) show positive curvature compared to the standard WHHM model. As $\lambda_{\mathrm{tr}}$ decreases, we see a consistent rise in the curvature value, expressed by measuring $h/(1-t)$, where $h=B_{c2}(T)/B_{c2}(0)$ is the reduced field and $t=T/T_{c}$ is the reduced temperature. We will compare to Nb films produced in other labs. [Preview Abstract] |
Thursday, November 19, 2015 9:54AM - 10:06AM |
A2.00008: Irradiation of commercial, high-Tc superconducting tape for potential fusion applications: effect on bulk pinning force density Albert Gapud Effects of low dose ion irradiation on the electrical transport current properties of commercially available high-temperature superconducting, coated-conductor tapes were recently investigated, in view of potential applications in the irradiative environment of fusion reactors. Three different tapes, each with unique as-grown flux-pinning structures, were irradiated with Au and Ni ions at energies that provide a range of damage effects, with expected accumulated damage levels. Field- and temperature-dependent measurements of transport current show only modest detriment to as-grown pre-irradiation properties; in one case critical currents may have even been enhanced. To investigate the effect of irradiation on bulk flux pinning in more detail, pinning-force curves have been evaluated using the model by Dew-Hughes [\textit{Physical Review }\textbf{140, }A1197 (1965)] -- as will be discussed. [Preview Abstract] |
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