Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session C35: Oxide Surfaces and Interfaces |
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Sponsoring Units: DCMP Chair: Phil Sprunger, Louisiana State University Room: 298 |
Monday, March 13, 2017 2:30PM - 2:42PM |
C35.00001: First-Principles Studies on Deoxidizing Mechanism of V$_{\mathrm{2}}$O$_{\mathrm{5}}$ via Hydrogen yanning Zhang, mengting Jin With its high melting point, good plasticity and good corrosion resistance at low temperatures, vanadium has been widely used in the industries of iron and steel, aviation, energy storage, etc. However, the traditional manufacturing technologies of pure vanadium are usually connected with complex manufacturing processes, high costs and serious environment pollution, which more or less hindered its further applications. Recently, hydrogen gas has been considered as a promising reducing agent of V$_{\mathrm{2}}$O$_{\mathrm{5}}$, but experimental studies of deoxidization process of V$_{\mathrm{2}}$O$_{\mathrm{5}}$ single crystal surfaces were found to be extremely difficult. In this work, we perform extensive \textit{ab initio} studies on~the structural and electronic properties of different V$_{\mathrm{2}}$O$_{\mathrm{5}}$ surfaces, as well as the adsorption sites, diffusion and desorption processes of H on these surfaces as a dependence of depth. We found that H atoms adsorb at oxygen site to form surface hydroxyl (OH$^{\mathrm{-}})$ and further to form H$_{\mathrm{2}}$O on V$_{\mathrm{2}}$O$_{\mathrm{5}}$(010) surfaces, and the latter is easier to be desorbed compared with the former. But the desorption of H$_{\mathrm{2}}$O causes significant surface reconstructions, which makes the further deoxidization of V$_{\mathrm{2}}$O$_{\mathrm{5}}$ difficult, particularly on the V$_{\mathrm{2}}$O$_{\mathrm{5}}$ single-layer. Our theoretical results are instructive for understandings of the reduction mechanism of V$_{\mathrm{2}}$O$_{\mathrm{5}}$ by using a green agent of H$_{\mathrm{2}}$, and furthermore for the design of new experiments$_{\mathrm{.}}$ [Preview Abstract] |
Monday, March 13, 2017 2:42PM - 2:54PM |
C35.00002: First-principles Study of CeO2/BiVO4 Interfaces Guo Li, Aniketa Shinde, Lan Zhou, Dan Guevarra, Santosh Suram, Francisca Toma, Qimin Yan, Joel Haber, John Gregoire, Jeffrey Neaton Using density functional theory calculations, we investigate the structural, energetic, and electronic properties of CeO2/BiVO4 interfaces. We find that, despite a 5\% mismatch, thin CeO2 layers (with thicknesses of up to three monolayers) can be epitaxially grown on BiVO4(010) substrates. At these epitaxial interfaces, all the atoms are fully coordinated. Thus, no localized interface state appears in the band gap. More importantly, the surface states of BiVO4, which serve as recombination centers for excited charges, are eliminated by the CeO2 coating layers. These findings explain the significant decrease of charge recombination observed in experiments. [Preview Abstract] |
Monday, March 13, 2017 2:54PM - 3:06PM |
C35.00003: Surface Coverage and Metallicity of ZnO Surfaces from First-Principles Calculations Xiao Zhang, Andre Schleife Zinc oxide (ZnO) surfaces are widely used in different applications such as catalysis, biosensing, and solar cells. These surfaces are, in many cases, chemically terminated by hydroxyl groups. In experiment, a transition of the ZnO surface electronic properties from semiconducting to metallic was reported upon increasing the hydroxyl coverage to more than approximately 80\,\%. The reason for this transition is not well understood yet. We report on first-principles calculations based on density functional theory for the ZnO $[10\bar{1}0]$ surface, taking different amounts of hydroxyl coverage into account. We calculated band structures for fully relaxed configurations and verified the existence of this transition. However, we only find the fully covered surface to be metallic. We thus explore the possibility for clustering of the surface-terminating hydroxyl groups based on total-energy calculations. We also found that the valence band maximum consists of oxygen p states from both the surface hydroxyl groups and the surface oxygen atoms of the material. The main contribution to the metallicity is found to be from the hydroxyl groups. [Preview Abstract] |
Monday, March 13, 2017 3:06PM - 3:18PM |
C35.00004: First-principles study of oxygen enhanced wettability of copper on O-terminated ZnO surface Eun-Ae Choi, Jung-Heum Yoon, Seung Zeon Han, Hak-Sung Lee, Chang-Seok Oh Ultrathin films of metals such as copper have attracted much attention as a favorable candidate for flexible transparent electrodes due to high electrical conductivity and good ductility. However, the growth of islands results in high sheet resistance and low transmittance of metal ultrathin films. Here, we suggest that oxygen at the initial stage of Cu deposition can suppress the growth of Cu islands on O-terminated ZnO surface. We perform the density functional calculations for formation energies and electronic structures of Cu thin films on ZnO surface. Our calculations show that oxygen atoms stabilize both of the Cu/ZnO interface and the surface of Cu thin films. In addition, we extract the spreading parameter (S) of Cu films based on the simulations, showing the complete wetting of Cu at low concentration of oxygen. Finally, we confirm experimentally oxygen enhanced wettability of Cu on O-terminated ZnO substrate. [Preview Abstract] |
Monday, March 13, 2017 3:18PM - 3:30PM |
C35.00005: Strain-induced oxygen vacancies in ultrathin epitaxial CaMnO$_{\mathrm{3}}$ films Ravini Chandrasena, Weibing Yang, Qingyu Lei, Mario Delgado-Jaime, Frank de Groot, Elke Arenholz, Keisuke Kobayashi, Ulrich Aschauer, Nicola Spaldin, Xiaoxing Xi, Alexander Gray Dynamic control of strain-induced ionic defects in transition-metal oxides is considered to be an exciting new avenue towards creating materials with novel electronic, magnetic and structural properties. Here we use atomic layer-by-layer laser molecular beam epitaxy to synthesize high-quality ultrathin single-crystalline CaMnO$_{\mathrm{3}}$ films with systematically varying coherent tensile strain. We then utilize a combination of high-resolution soft x-ray absorption spectroscopy and bulk-sensitive hard x-ray photoemission spectroscopy in conjunction with first-principles theory and core-hole multiplet calculations to establish a direct link between the coherent in-plane strain and the oxygen-vacancy content. We show that the oxygen vacancies are highly mobile, which necessitates an in-situ-grown capping layer in order to preserve the original strain-induced oxygen-vacancy content. Our findings open the door for designing and controlling new ionically active properties in strongly-correlated transition-metal oxides. [Preview Abstract] |
Monday, March 13, 2017 3:30PM - 3:42PM |
C35.00006: Evolution of the Electronic Structure of $n$-Type BaSnO${}_3$ Films With Chemical Doping and Photodoping Edward Lochocki, Hanjong Paik, Masaki Uchida, Darrell Schlom, Kyle Shen Lanthanum-doped barium stannate (La:BaSnO${}_3$) is a transparent conducting oxide well known for its high mobility and its ability to host a surface electron gas. Here we present angle-resolved photoemission (ARPES) measurements of La:BaSnO${}_3$ thin films deposited on scandate substrates by molecular beam epitaxy. Increased bulk La content is found to reduce the surface carrier concentration via Fermi level pinning, in contrast to other $n$-type transparent conducting oxides. Subsequent ARPES measurements made over the course of hours show that photogenerated electron-hole pairs reduce the upward band bending, providing persistent but reversible surface photodoping. Chemical doping and photodoping both induce spectral changes typically associated with oxygen vacancy formation or electronic correlations, even though BaSnO${}_3$ exhibits extreme oxygen stability and its valence and conduction bands have no $d$ character. These results establish BaSnO${}_3$ as a unique transparent conductor and demonstrate its potential for understanding the broader class of perovskite oxide materials. [Preview Abstract] |
Monday, March 13, 2017 3:42PM - 3:54PM |
C35.00007: Abstract Withdrawn
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Monday, March 13, 2017 3:54PM - 4:06PM |
C35.00008: Electron transport properties of Cadmium Oxide thin films grown by molecular beam epitaxy Yu Yun, Songsheng Tao, Yang Ma, Wenyu Xing, Yangyang Chen, Tang Su, Qi Song, Wei Yuan, Xi Lin, X. C. Xie, Wei Han Oxide electronics has drawn significant attention because of its potential application in future electronic and optical devices. In this study, we have fabricated high quality CdO and La-doped CdO thin films on MgO substrates by oxide molecular beam epitaxy. The crystal structure is characterized by X-ray diffraction, and the electron mobility is studied using van der Pauw method. We have found that the electron mobility is dominated by the ionized impurity scattering below 50 K, and longitudinal optical phonon scattering dominates from 50 to 300 K with a longitudinal optical phonon energy of about 41 eV. The electron mobility first increases with the La doping, reaching the maximum value of electron mobility at 2 K of around 520 cm2V-1s-1 at carrier density about 1.4x1020 cm-3, and then falls as the doping increases. [Preview Abstract] |
Monday, March 13, 2017 4:06PM - 4:18PM |
C35.00009: Polarity-induced persistent surface reconstruction in SrRuO$_{\mathrm{\mathbf{3}}}$\textbf{ (111) thin films}. Weimei Xie, Mohammad Saghayezhian, M.Q. Gu, Hangwen Guo, X.S. Wu, E.W. Plummer, Jiandi Zhang The surface structural and electronic properties of SrRuO$_{\mathrm{3}}$/SrTiO$_{\mathrm{3\thinspace }}$(111) as function of the film thickness are investigated. It is found that, though the interface of SRO/STO (111) has no polar mismatch and negligible lattice mismatch, the polar surface of SrRuO$_{\mathrm{3}}$ (111) thin films results in a persistent surface reconstruction. Above 2 unit cells, a $(\sqrt 3 \times \sqrt 3 )R30^{\circ}$ surface reconstruction is observed with both Low energy and reflection high energy electron diffraction. X-ray photoemission spectroscopy shows that the reconstruction is associated with the ordered oxygen vacancies on SrO$_{\mathrm{3-\delta }}$ terminated surface to compensate the surface polarity. Post annealing in oxygen/ozone mixture restores the $p$(1$\times$ 1) surface structure, but results in different surface relaxation and enhances the metallicity thus reducing the thickness of dead layer in this material. [Preview Abstract] |
Monday, March 13, 2017 4:18PM - 4:30PM |
C35.00010: Transport Physics Mechanisms in Thin-Film Oxides$^{\mathrm{1}}$. Brian D. Tierney, Harold P. Hjalmarson, Robin B. Jacobs-Gedrim, Conrad D. James, Matthew M. Marinella A physics-based model of electron transport mechanisms in metal-insulating oxide-metal (M-I-M) systems is presented focusing on transport through the metal-oxide interfaces and in the bulk of the oxide. Interface tunneling, such as electron tunneling between the metal and the conduction band, or to oxide defect states, is accounted for via a WKB model. The effects of thermionic emission are also included. In the bulk of the oxide, defect-site hopping is dominant. Corresponding continuum calculations are performed for Ta$_{\mathrm{2}}$O$_{\mathrm{5}}$ M-I-M systems utilizing two different metal electrodes, e.g., platinum and tantalum. Such an asymmetrical M-I-M structure, applicable to resistive memory applications or oxide-based capacitors, reveals that the current can be either bulk or interface limited depending on the bias polarity and concentration of oxygen vacancy defects. Also, the dominance of some transport mechanisms over others is shown to be due to a complex interdependence between the vacancy concentration and bias polarity.$^{\mathrm{1}}$Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Monday, March 13, 2017 4:30PM - 4:42PM |
C35.00011: Impact of Strong Forward Scattering Electron-Phonon Coupling at the SrTiO3 Interface Benjamin Nosarzewski, Edwin Huang, Brian Moritz, Yao Wang, Thomas Devereaux Recent experiments have demonstrated the importance of electron-phonon coupling strongly peaked at small momentum transfer in enhancing superconductivity and providing strong band renormalizations in both monolayer FeSe films on SrTiO$_3$ (STO) as well as bulk STO. This coupling to the LO$_4$ phonon in STO also was found to be sensitive to the screening of doped carriers in the surface state, whose shallow band bottom precludes perturbative treatment of the coupling. Using microscopic models and many-body algorithms, we characterize spectra and trends of superconductivity via a doping dependence of the effective electron-phonon coupling. We discuss our results in terms of the ratio of the lattice to kinetic energy and highlight the role of screening. [Preview Abstract] |
Monday, March 13, 2017 4:42PM - 4:54PM |
C35.00012: Spin-Orbit Interaction and Kondo Scattering at the PrAlO$_3$/SrTiO$_3$ Interface Shirin Mozaffari, Samaresh Guchhait, John Markert We have investigated the effect of oxygen content, in the $P_{O_{2}}$ range of $6\times10^{-6}$ -- $1\times10^{-3}$ torr, on the spin-orbit (SO) interaction at PrAlO$_3$/SrTiO$_3$ interface. The most-conducting 2-D-like PrAlO$_3$ interfaces were not as conducting as comparable LaAlO$_3$ samples, indicating either a steric or mixed-valent effect. The least-conducting, most oxygenated PrAlO$_3$ interface exhibits hole conductivity, a departure from the typical electron-doped behavior. For $10^{-5}$ and $10^{-4}$ torr samples, high-temperature metallic behavior is accompanied by an upturn in resistivity at low temperatures, consistent with Kondo scattering theory; analysis gives a Kondo temperature $ \sim $17 K. The magnetoresistance (MR) for the low $P_{O_{2}}$-grown samples was modeled with a positive part due to weak anti-localization (WAL) from a strong SO interaction, and a negative part due to the Kondo effect. The variation of MR suggests a strong SO interaction for the $10^{-5}$ torr sample with $H_{SO}=$1.25 T in both field orientations. The WAL effect is smaller for higher $P_{O_{2}}$-grown samples, where the high-field MR is dominated by the Kondo effect. [Preview Abstract] |
Monday, March 13, 2017 4:54PM - 5:06PM |
C35.00013: Electrical Transport and Magnetoresistance Properties of Tensile-Strained CaMnO3 Thin Films Dustin Ullery, Bridget Lawson, William Zimmerman, Samuel Neubauer, Adeel Chaudhry, Cacie Hart, Grace Yong, Vera Smolyaninova, Rajeswari Kolagani We will present our studies of the electrical transport and magnetoresistance properties of tensile strained CaMnO3 thin films. We observe that the resistivity decreases significantly as the film thickness decreases which is opposite to what is observed in thin films of hole doped manganites. The decrease in resistivity is more pronounced in the films on (100) SrTiO3, with resistivity of the thinnest films being about 3 orders of magnitude lower than that of bulk CaMnO3. Structural changes accompanying resistivity changes cannot be fully explained as due to tensile strain, and indicate the presence of oxygen vacancies. These results also suggest a coupling between tensile strain and oxygen deficiency, consistent with predictions from models based on density functional theory calculations. We observe a change in resistance under the application of moderate magnetic field. Experiments are underway to understand the origin of the magnetoresistance and its possible relation to the tensile strain effects. [Preview Abstract] |
Monday, March 13, 2017 5:06PM - 5:18PM |
C35.00014: The electronic structure and phase separation of LuFeO$_{\mathrm{3}}$ Shi Cao, Xiaozhe Zhang, Kishan Sinha, Wenbin Wang, Jian Wang, Peter Dowben, Xiaoshan Xu The conduction band electronic structure of hexagonal and orthorhombic LuFeO$_{\mathrm{3}}$ thin films have been measured using x-ray absorption spectroscopy (XAS) at iron L edge and oxygen K edge. Dramatic differences in both the spectral features and the linear dichroism are observed. These differences in the spectra can be explained using the differences in crystal field splitting of the metal (Fe and Lu) electronic states and the differences in O 2p-Fe 3d and O 2p-Lu 5d hybridization. Segregation of the hexagonal and orthorhombic phases has been identified by X-ray Photo-electron Emission Microscopy (X-PEEM) indicating that the hexagonal to orthorhombic phase transition includes co-existence of phases at room temperature. [Preview Abstract] |
Monday, March 13, 2017 5:18PM - 5:30PM |
C35.00015: The delayed theory of fields Jaber Poormohammadi, hessam rezagholizadeh The idea of action immediate propagation has been in physicists' mind from the beginning, until Faraday raised the idea of delayed propagation. Using this idea and the delayed theory of fields, we face consequences which can be interesting for anyone who has learned physics. We can mention non-equivalency between stationary frames and moving frames, dependency of field to medium, different velocity barriers for different mediums and non-equivalency of inertial reference frames are among these consequences. By designing an experiment we can challenge this theory and its consequences. All of these sections processed in the article titled "The delayed theory of fields". [Preview Abstract] |
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