Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K17: Kinetics & Dynamics in Surfaces, Interfaces, and Thin Films |
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Sponsoring Units: DCMP DMP Chair: Brad Conrad, SPS Room: LACC 306A |
Wednesday, March 7, 2018 8:00AM - 8:12AM |
K17.00001: High Catalytic Activity of Singly Distributed Pd1/ZnO(10-10) toward Methanol Partial Oxidation: A DFT based Accelerated Kinetic Monte Carlo Study Sampyo Hong, Takat Rawal, Shree Ram Acharya, Talat Rahman We have performed accelerated kinetic Monte Carlo (KMC) simulations for methanol partial oxidation on Pd1/ZnO(10-10) and Pd16Zn16 nanocluster systems based on the energetics and kinetic parameters derived from our recent density functional theory (DFT) calculations for both systems. In agreement with recent experiment [1] our simulations confirm that H2 selectivity of the singly dispersed Pd1/ZnO is ~97%, by far higher than that of Pd16Zn16, only ~50%. Our combined DFT+KMC simulations provide insights into high activity and selectivity of Pd1/ZnO. We find that singly-distributed Pd sites induce substantial modification of the local geometrical and electronic structures of Zn sites. Singly distributed Pd sites serve as the active sites for H2 adsorption. Furthermore, they provide the strong adsorption for methanol, induce the spontaneous CO2 formation and nearly spontaneous dissociation of H2O, and the stabilization of H2 right at or near the sites, thereby decisively enhancing H2 and CO2 selectivity. For Pd1/ZnO catalyst, we find that CO2 formation occurs via O*+CO*→CO2* and an alternative pathway (dissociation of H2COO* and HCOO*) is kinetically unfavorable. |
Wednesday, March 7, 2018 8:12AM - 8:24AM |
K17.00002: Computational Approach to Water Adsorption on TiO2-Anatase(101): Insights from Periodic Slab and Embedded Cluster Calculations Thorben Petersen, Thorsten Klüner The efficient splitting of water nowadays represents one of the major scientific challenges.[1] To further progress within this research field, an understanding of the elementary mechanisms is crucial. |
Wednesday, March 7, 2018 8:24AM - 8:36AM |
K17.00003: Understanding of solid/liquid and solid/gas interfaces in reactions from the in-situ/operando soft x-ray spectroscopy Jinghua Guo, Yi-Sheng Liu, Per-Anders Glans The energy materials and devices have been largely limited in a framework of thermodynamic and kinetic concepts or atomic and nanoscale, which rests in large on fundamental understanding of the physical and chemical interfacial processes. Soft x-ray techniques offer unique characterization in many important energy materials and catalysis in regards to the functionality, complexity of material architecture, chemistry and interactions among constituents within. The presentation gives brief accounts of energy materials and catalysis research using soft x-ray spectroscopy, scattering and imaging capabilities at the 3rd generation light source. |
Wednesday, March 7, 2018 8:36AM - 8:48AM |
K17.00004: Time-Resolved and Space-Resolved Study of Iron Oxide Nanoparticle Self-Assembly on Liquid Surfaces by Using In-Situ Small Angle X-Ray Scattering Jiayang Hu, Brady Pan, Evan Spotte-Smith, Ni Huo, Irving Herman Real time in-situ synchrotron small-angle X-ray scattering (SAXS) is used to follow the formation of ordered monodisperse iron oxide nanoparticle (NP) monolayers (MLs) at multiple positions after an NP heptane dispersion is drop-cast on diethylene glycol (DEG). One and only one close-packed hexagonal ML is formed at the heptane/DEG interface before the heptane totally evaporates, while the remaining NPs are still dispersed in the heptane bulk. Optical reflection is also used to monitor ML formation. |
Wednesday, March 7, 2018 8:48AM - 9:00AM |
K17.00005: Prevention of surface recombination by electrochemical tuning of TiO2-passivated photocatalysts Bingya Hou, Fatemeh Rezaeifar, Jing Qiu, Guangtong Zeng, Rehan Kapadia, Steve Cronin We present a systematic study of photoluminescence (PL) spectroscopy of TiO2-passivated GaAs as a function of electrochemical potential in an ionic liquid solution.[1] We observe a 7X increase in the PL intensity as the GaAs transitions from accumulation to depletion due to the applied potential. We attribute this to the excellent control over the surface Fermi level enabled by the high capacitance of the electrochemical double layer and TiO2. In addition to photoluminescence (PL) spectroscopy, we also measured the capacitance-potential (i.e., C-V) characteristics of these samples, which indicate flat band potentials that are consistent with these regimes of ion accumulation observed in the photoluminescence measurements. We have also performed electrostatic simulations of these C-V characteristics, which provide a detailed and quantitative picture of the conduction and valence band profiles and charge distribution at the surface of the semiconductor. These simulations also enable us to determine the range of potentials over which the semiconductor surface experiences depletion, inversion, and accumulation of free carriers. |
Wednesday, March 7, 2018 9:00AM - 9:12AM |
K17.00006: Microscopic Spin-Orbit Torque in 3d-5d Transition Metal Bilayers Based on Tight-Binding Model Yafei Ren, Junjie Zeng, Tao Hou, Hui Yang, Zhenhua Qiao, Allan MacDonald Transition metal has attracted much attention both from fundamental physics and practical applications due to either the magnetization of 3d transition metals or strong spin-orbit coupling of 5d ones. Their combination at the interface of 3d-5d transition metal thin films leads to a variety of intriguing emergent phenomena, which are, however, not yet clearly understood. To give a realistic but strongly tunable description of these systems, we theoretically study the electronic structure of 3d and 5d transition-metal thin films by using first-principles' calculation and construct the corresponding tight-binding Hamiltonian on the basis of s, d, and pz orbitals by employing two-center approximation based on Slater-Koster table. Non-linear least square fitting is employed to determine the tight-binding parameters. Based on this microscopic model, we further study the spin-orbit torque at the 3d-5d transition-metal bilayers by non-equilibrium Green's function method. |
Wednesday, March 7, 2018 9:12AM - 9:24AM |
K17.00007: First-Principles Simulations on the Microscopic Mechanism of Smart Water Enhanced Oil Recovery Yun-Peng Wang, Sebastian Zuluaga, Sokrates Pantelides The continuously increasing demand for petroleum and related products calls for the enhancement of crude oil recovery from fractured and low-permeability carbonate reservoirs. Seawater injection has been found to enhance oil recovery and laboratory experiments have revealed that oil recovery can be enhanced by tuning the ionic composition of the injecting brine, but no consensus has been achieved on the underlying microscopic mechanism. In this work, we consider the oil recovery as a friction problem [1] with a thin brine film at the oil/rock interface serving as a lubricant. Inorganic ions, such as Na+, Ca2+, Mg2+, and SO42- modify the water structure and hence are expected to change the lubricant friction property. First-principles molecular dynamics simulations were carried out, revealing the corresponding changes in the friction properties. Comparison with experimental data and a discussion of the atomic-scale interactions underlying the changes in friction will be given. |
Wednesday, March 7, 2018 9:24AM - 9:36AM |
K17.00008: Methane dissociation on the steps and terraces of Pt(211) resolved by quantum state and impact site Rainer Beck, Helen Chadwick, Ana Gutiérrez-González Methane dissociation on the step and terrace sites of a Pt(211) single crystal was studied by reflection absorption infrared spectroscopy (RAIRS). The infrared absorption signal due to chemisorbed methyl species, CH3(ads), was used to distinguish between absorption on step and terrace sites. CH3(ads) uptake on Pt(211) was monitored as a function of kinetic energy and quantum state of the incident CH4, for both step and terrace sites indicating a direct dissociation mechanism on both sites with higher reactivity on steps than on terraces consistent with a difference in activation barrier height of at least 30 kJ/mol. For the dissociation of the partially deuterated methane CH3D, excitation of the antisymmetric C-H stretch vibration v4 enables for bond selective C-H cleavage either selectively only on the steps or on both steps and terrace sites depending on the incident kinetic energy. |
Wednesday, March 7, 2018 9:36AM - 9:48AM |
K17.00009: Adsorption and dissociation processes of water on tungsten trioxide (001) from first principles Thomas Teusch, Thorsten Klüner Photocatalytic water splitting is a cutting-edge topic nowadays since there is no environmental friendly and efficient way known for hydrogen production. A promising material in this context is tungsten trioxide, which has on the one hand a suitable band gap and an appropriate valence band position for oxygen production, but on the other hand an unsuitable conduction band position for hydrogen evolution [1]. |
Wednesday, March 7, 2018 9:48AM - 10:00AM |
K17.00010: Annealing Effects on Bulk and Surface Properties of Lithium Niobate Christopher Keck, Mario Rodriguez, Uday Singh, Sara Callori, Mark Koten, Jeffrey Shield, Le Zhang, Xuegang Chen, Xia Hong, Shireen Adenwalla Surface acoustic waves (SAW) on lithium niobate (LiNbO3) are being used to investigate the effects of fast strain on complex oxide thin films. Successful deposition requires annealing to achieve suitable crystallinity, motivating this study. Surface properties were investigated by depositing interdigital transducers on LiNbO3 and annealing at 500, 600, and 800 °C. Power spectrum and pulse response measurements done before and after annealing indicate that the transmitted power from the SAW degrades at 800 °C. The bulk piezoelectric coefficient was measured, before and after annealing at 800 °C, to be 17 pm/V and 21 pm/V. This improvement in the bulk performance is at odds with the surface behavior. In a related study, Sm0.60Nd0.40NiO3 (SNNO) was deposited on a wafer of LiNbO3 at a temperature of 500 °C in an atmosphere of argon and oxygen. Transmission electron microscopy measurements indicate that the SNNO was amorphous while the interfacial structure of the LiNbO3 went from a rhombohedral to a monoclinic phase. Providing an explanation for the less than optimal crystallinity of nickelate films grown on the surface. |
Wednesday, March 7, 2018 10:00AM - 10:12AM |
K17.00011: Surface reconstruction of half-Heusler semiconductors – CoTiSb and NiTiSn Abhishek Sharan, Jason Kawasaki, Chris Palmstrom, Anderson Janotti Heusler materials are an exciting category of materials and are believed to be ternary cousins to III-Vs, exhibiting wider range of electronic and magnetic properties than III-Vs. These materials can be grown on III-Vs and can potentially be integrated into novel electronic devices. Many of the electronic applications depend on electronic surface states, like spin injection in MTJs. Therefore, it is critical to understand the surface structure and electronic properties, and the driving forces of surface reconstruction in these materials. CoTiSb and NiTiSn are representative of a large class of 18 valence electron count half-Heusler materials, and have demonstrated promising applications in energy related fields. Here we explore the mechanisms of surface reconstruction of CoTiSb and NiTiSn (001) using density functional theory calculations. We present a simple electron counting model which explains the stability and driving force for Sb-Sb or Sn-Sn dimerization, similar to conventional semiconductors. We find that the (001) surface is metallic due to unsatisfied dangling bonds and that the surface energy is minimized by forming Sb-Sb or Sn-Sn dimers at low Ti surface coverage. We then compare our theoretical results with available experimental data. |
Wednesday, March 7, 2018 10:12AM - 10:24AM |
K17.00012: Adsorption and decomposition of organophosphonates on MoO2: A DFT and APXPS study Roman Tsyshevskiy, Ashley Head, Lena Trotochaud, Bryan Eichhorn, Hendrik Bluhm, Maija Kuklja Our knowledge of interactions of toxic chemical warfare agents (CWAs) with existing filter materials is scarce, as experiments with these toxic agents required special facilities and hence they are beyond capabilities of most research groups. DFT modeling provides an opportunity to explore various physical and chemical properties of CWAs including their reactivity in the gas phase, liquid solutions and interfaces with filter materials. While outcome of the modeling depends on many factors, results of experimental measurements can serve as reference data and validation for theoretical studies. We report results of our joint APXPS and DFT study of interactions of organophosphonate compounds with a MoO2 surface. Solid state periodic calculations were initially used to aid with an interpretation of APXPS measurements to explore adsorption and decomposition of DMMP on MoO2 surface. Once the good qualitative agreement between theory and experiment was established, DFT modeling was employed to investigate mechanisms of decomposition of highly toxic sarin on MoO2 (011) surface. |
Wednesday, March 7, 2018 10:24AM - 10:36AM |
K17.00013: Coordinated Computational and Experimental Study of Oxide Formation Tuning on Cu Surfaces Matthew Curnan, Meng Li, Christopher Andolina, Wissam Saidi, Judith Yang Past research indicates that high density, discontinuous Cu oxide islands are preferentially formed close to Cu surface facets, while low density, continuous Cu oxide films are developed at high temperatures. However, the tunability of Cu surface oxide nucleation and growth behavior with simultaneous consideration of particular facet defects and thermodynamic conditions, in addition to oxidation mechanisms prevailing during nucleation and growth, have not been comprehensively assessed. Investigating these gaps in current research, we apply a Cu/O Reactive Force Field (RFF) trained using data from Density Functional Theory (DFT) and experimental results to complete Molecular Mechanics (MM) and Dynamics (MD) calculations modeling O diffusion dynamics and resulting atomic O densities. Firstly, we determine the extent to which O densities modeling early stage Cu oxidation can predict late stage Cu oxide nucleation behavior, linking them via the oxidation mechanisms enabling O and oxide density comparisons. Subsequent MD results will be applied to characterize oxide formation tuning over experimental conditions of interest. |
Wednesday, March 7, 2018 10:36AM - 10:48AM |
K17.00014: Abstract Withdrawn
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Wednesday, March 7, 2018 10:48AM - 11:00AM |
K17.00015: Watching hydrogen interaction with graphene: an ab initio molecular dynamics study using embedded mean-field theory Feizhi Ding, Thomas Miller Reaction of H atoms with graphene-like surfaces is fundamental for interstellar research, hydrogen storage, and graphene-based spintronics. Ab initio molecular dynamics (AIMD) simulations can play an important role in obtaining detailed, dynamical understanding of this process. However, this simple system poses significant challenges for current theoretical approaches. For example, different electronic structure methods predict distinct adsorption barriers; nuclear quantum effects are important and should be included in the simulations; large size of the graphene system is required to capture the phonon bending and conformational fluctuations; necessary inclusion of exact exchange interactions and the use of large system size make the standard AIMD simulations prohibitively expensive. Here, we present AIMD simulations of H-atom reactive scattering using the embedded mean-field theory (EMFT), which allows for on-the-fly ab initio calculations of the energy and forces with hybrid-DFT accuracy but at the much lower cost of LDA level. Nuclear quantum effects are also accounted for by combining EMFT with the path-integral-based ring-polymer molecular dynamics method. Our simulation results have shown to give excellent agreement with experimental results obtained by the Wodtke group. |
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