Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J52: Oxide Films, Surfaces, and Interfaces |
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Sponsoring Units: DCMP Chair: Wennie Wang, University of Chicago Room: Mile High Ballroom 1E |
Tuesday, March 3, 2020 2:30PM - 2:42PM |
J52.00001: Microstructure structure of air-grown UNxOy on nitrogen-rich uranium nitride Xiaofang Wang, Zhong Long, Rongguang Zeng, Yin Hu, Kezhao Liu Uranium nitrides have aroused great attention for their important application in the corrosion protection of metallic uranium, due to formation of a nanoscale surface oxide layer when exposed to air or an oxygen-including atmosphere that slows or protects against further oxidation, but direct observations on the microstructure of oxide layer and the relationship of the crystal structure between the oxide layer and the underlying uranium nitride remain unresolved. In this work, oxide formation on surface of nitrogen-rich uranium nitride was investigated using X-ray photoelectron spectroscopy (XPS), auger electron spectroscopy (AES), aberration-corrected transmission electron microscopy (TEM), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) coupled with electron energy-loss spectroscopy (EELS). XPS and AES studies indicated that the oxidized layer on UN2-x film is ternary compound uranium oxynitride (UNxOy) in about 10 nm thickness. TEM/HAADF-STEM and EELS studies revealed the UNxOy crystallizes in the FCC CaF2-type structure with the lattice parameter close to the CaF2-type UN2-x matrix. The work can provide further information to the oxidation mechanism of uranium nitride. |
Tuesday, March 3, 2020 2:42PM - 2:54PM |
J52.00002: Segregation Effects and Charge Transport in Yttria-Stabilized Zirconia Thin Films on Langasite Substrates Firas Mahyob, George Bernhardt, Robert Lad Yttria-stabilized zirconia (YSZ) is widely used as a bulk ceramic in solid-state oxygen sensors due to its high ionic conductivity, chemical inertness, and stability up to 1500oC. In thin film form, YSZ is an attractive component for use in wireless microwave acoustic sensors to monitor conditions within harsh industrial environments. In this work, RF-magnetron sputter deposition was used to synthesize YSZ (8%Y2O3-92%ZrO2) films with thicknesses from 15nm to 200nm on piezoelectric langasite (La3Ga5SiO14) substrates at growth temperatures from 25-600oC. X-ray diffraction indicated that the cubic YSZ films grow with preferred (111) out-of-plane texture on the langasite substrate with random in-plane orientation. Scanning electron microscopy revealed the presence of stress hillocks at the YSZ/langasite interface, and this was minimized at a 400oC deposition temperature where extremely smooth films were obtained as determined by x-ray reflectivity. Post-deposition air annealing caused yttria segregation to the film surface region as evidenced by increases in the Y3d/Zr3d photoelectron peak area ratio upon annealing up to 1000oC. This segregation is accompanied by an increase in film ionic conductivity and larger YSZ grain size as measured by high temperature impedance spectroscopy. |
Tuesday, March 3, 2020 2:54PM - 3:06PM |
J52.00003: Surface reconstruction of TiO2 nanocrystals Aram Yoon, Xiao Zhang, Andre Schleife, Jian-Min Zuo One of the best studied photocatalysts is TiO2. As chemical reactions occur on surfaces, the surface of TiO2 has been extensively investigated [1]. However, focus has largely been on 2D surfaces of bulk crystals, while real catalysts are nanocrystals or nanoparticles. Surface reconstruction on a nanocrystal is expected to be different with multiple facets. Here, we report on reconstructed surfaces on rutile nanocrystals studied by environmental transmission electron microscopy [2]. The reconstruction is imaged using an electron direct detection detector (DDD). The DDD provides significantly improved signal/noise ratio and high spatial resolution. Using these new approaches [3], we observed the surfaces of {110}, {210}, and {100} on TiO2 nanocrystals at atomic resolution and compared with previous models and with DFT calculations of atomic positions and total energies. Most importantly, the results allow an examination of surface reconstruction dependence on nanocrystal sizes. |
Tuesday, March 3, 2020 3:06PM - 3:18PM |
J52.00004: Epitaxial Growth of Sr3Al2O6 by Pulsed Laser Deposition as a Water-Soluble Sacrificial Layer for GaAs Deposition Imran Khan, Bill McMahon, Andrew Norman, Andriy Zakutayev Despite the record high efficiency for GaAs solar cells, its terrestrial application is limited due to both the particularly high costs related to the required single crystal substrates and the epitaxial growth. A water-soluble lift off layer could reduce costs by avoiding the need for toxic etchants, substrate re-polishing and expensive process steps. |
Tuesday, March 3, 2020 3:18PM - 3:30PM |
J52.00005: Surface and Interface Energetics of Pyrite-type Materials Joseph Minnich, Andrew O'Hara, Sokrates T Pantelides Materials with the pyrite crystal structure, such as iron and cobalt sulfide, are composed of earth-abundant |
Tuesday, March 3, 2020 3:30PM - 3:42PM |
J52.00006: Atomic scale dynamic process of oxide growth during copper oxidation Meng Li, Matthew T Curnan, Wissam A Saidi, Judith Yang Understanding oxide growth mechanism during metal oxidation is essential for rational design and control of oxides for applications in catalysts, sensors, as well as corrosion protection. Despite ample research on bulk oxidation, little is known on the initial oxide growth process. In this work, we use correlated in situ Environmental Transmission Electron Microscope, DFT simulation, quantitative data extraction and statistical analysis to investigate the dynamic atomic process of initial oxide growth. An unusual layer-by-layer growth of Cu2O island along Cu2O(110) plane is observed, instead of along the previously assumed Cu2O(100) plane that is parallel to the Cu surface. Statistical analysis of growth dynamics indicates a diffusion limited monolayer growth process. DFT results showed Cu2O(110) has lower surface energy, favorable Cu and O diffusion barriers and adsorption energies during oxidation, leading to easier Cu2O monolayer formation along Cu2O(110). These results shed new light on surface oxidation process. |
Tuesday, March 3, 2020 3:42PM - 3:54PM |
J52.00007: Structure and electro-optical properties of SrxBa1-xNb2O6 films grown by molecular beam epitaxy. Ilya Beskin, Jacqueline Geler Kremer, Agham Posadas, Alexander Demkov With the rise of processor speed, optical fibers are replacing copper wires in carrying data between computer boards. Silicon photonics has applications in not only chip interconnects, but also neuromorphic and quantum computing. The Pockels effect offers a way to build fast, low power modulators of optical signals. The Pockels effect uses an electric field to change the index of refraction in a material. One can make devices that encode or alter information using the phase of light. SrxBa1-xNb2O6 (SBN) has been shown to have one of the highest available Pockels coefficients (~850pm/V). SBN was grown by molecular beam epitaxy on SrTiO3 (STO) substrates and STO can be used to integrate materials on Si. The growth was monitored with Reflective High Energy Electron Diffraction. Composition and oxidation states were measured in-situ by X-Ray Photoemission Spectroscopy. X-Ray Diffraction was used to verify the crystal phase and orientation of the SBN crystal. |
Tuesday, March 3, 2020 3:54PM - 4:06PM |
J52.00008: Probing TiO2 as a potential filter material for adsorption and destruction of chemical warfare agents Roman Tsyshevskiy, Monica McEntee, Erin Durke, Tianyu Li, Matthew Leonard, Efrain Rodriguez, Christopher Karwacki, Maija M Kukla An atomistic level understanding of mechanisms of adsorption and decomposition of chemical agents on components of filtration materials is required for improvements of existing and design of new materials for chemical protection. Here, we present a comprehensive study of sarin interactions with TiO2 performed by means of quantum chemical calculations and a combination of IR and XPS measurements. Computational modeling was used to reveal mechanisms of sarin adsorption and decomposition on an ideal (defect free) and hydroxylated TiO2 rutile (110) and anatase (101) surfaces, whereas experimental measurements were performed for TiO2 nanoparticles and synthesized mesoporous materials. Calculations revealed strong adsorption of sarin on both the ideal rutile and anatase surfaces, although high activation barriers preclude a decomposition of sarin. The presence of water, on the other hand, reduces binding strength of sarin to rutile and anatase, but promotes the decomposition of sarin. Results of computational modeling were found in good agreement with experimental measurements. |
Tuesday, March 3, 2020 4:06PM - 4:18PM |
J52.00009: Density Functional Theory Calculations of Al doped Hafnia for Different Crystal Symmetry Configurations Joshua Steier, Mehmet Alper Sahiner, Rory J Vander Valk, Jared Savastano, Stephen Kelty Thin films of Hf based oxides gained importance after the discovery of the ferroelectricity in these materials1. One of the ways to achieve ferroelectricity in HfO2 is doping with metals such as Zr and Al to modify the crystal structure towards orthorhombic symmetry. In Hf based oxide thin films prepared by doping, multiple crystal phases could emerge. In this work, we theoretically investigated the stability of the possible structures that could be present in Al doped HfO2 using quantum mechanical methods. Specifically, using plane wave density functional theory, the monoclinic, tetragonal, orthorhombic, and rhombohedral phases of aluminum doped hafnia were geometrically optimized. The resulting equilibrium structures for 3%, 6%, and 7% Al doped hafnia structures will be used as theoretical reference structures for EXAFS spectra obtained Al doped HfO2 thin films. |
Tuesday, March 3, 2020 4:18PM - 4:30PM |
J52.00010: Investigation of the thickness-dependent optical properties of ZnO films on Si and SiO2 substrates from the Mid-infrared to the Vacuum-ultraviolet using UV and FTIR spectroscopic ellipsometry Nuwanjula Samarasingha Arachchige, Stefan Zollner, Dipayan Pal, Aakash Mathur, Ajaib Singh, Rinki Singh, Sudeshna Chattopadhyay The conventional approach to describe the dielectric function ε as a sum of oscillators sometimes fails because each term only has a single broadening parameter. Instead, we find it more convenient to describe ε as a product of Drude, TO/LO phonon, and electronic interband transition factors. Specifically, we explore the behavior of phonon and excitonic absorption in bulk zinc oxide (ZnO) and ZnO thin films grown on Si and SiO2 using UV/VIS and FTIR spectroscopic ellipsometry. We characterized the structural properties of our ZnO films with x-ray diffraction, x-ray reflectivity, and atomic force microscopy. |
Tuesday, March 3, 2020 4:30PM - 4:42PM |
J52.00011: Surface structure and electronic properties of a, b, and e polymorphs of Ga2O3 Tengfei Cao, Rohan Mishra Ga2O3 is an emerging wide-band-gap semiconductor that exhibits diverse phases with varying electronic properties. ε-Ga2O3, a metastable polymorph, has recently been reported to be a ferroelectric semiconductor with potential application in power and high-frequency electronics [1]. Although there have been numerous attempts to grow ε-Ga2O3 on various substrates, single-phase ε-Ga2O3 thin films have not been reported. An investigation of the stability of the surface of a, b, and e polymorphs of Ga2O3 can facilitate the synthesis of phase-pure thin films. Results of first-principles calculations of the surface stability of the three Ga2O3 polymorphs as a function of the chemical potential along with their electronic properties will be presented. The stability of its (001) polar surface of Ga2O3 as a function of polarization and thickness will be presented. Moreover, electronic structure calculations indicate a lack of quantum confinement in α-Ga2O3 thin-films. Finally, different substrate effects on the stability of the three Ga2O3 polymorphs will be talked. |
Tuesday, March 3, 2020 4:42PM - 4:54PM |
J52.00012: Atomistic determination of the surface structure of Cu2O (111) and Cu2O (110): experiment and theory Jeffrey Guest, Rui Zhang, Liang Li, Laszlo Frazer, Kelvin B. Chang, Kenneth R Poeppelmeier, Maria Chan Photocatalytic reactions on the surface of cuprous oxide (Cu2O) hinge on atomic scale structure of the defected Cu2O surfaces; however, to date, the atomic morphologies of these surfaces have not been unambiguously characterized. In this work, high-resolution ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) and density functional theory (DFT) calculations combined with STM simulations have been used to determine the structure of the defected (111) and (110) surfaces of a Cu2O bulk crystal. Under STM, the imaged Cu2O (111) surface is dominated by coordinatively unsaturated copper atoms, and atomic-scale defects including the Cu vacancy and the O-vacancy-induced local surface restructuring [1,2] are identified. The Cu2O(110) surface reveals aggregation of defects and periodic distortions of the atomic rows. |
Tuesday, March 3, 2020 4:54PM - 5:06PM |
J52.00013: Structural and Electrical Properties of Pulsed Laser Deposited Yttrium Doped Zirconium Oxide Thin Film Stabilization Matthew Melfi, Sarah Tuttle, Samantha Dalli, Kellen Murphy, Mehmet Alper Sahiner Solid Oxide Fuel Cells (SOFC) are devices that use electrochemical reactions to convert chemical energy from fuel to electricity. In comparison with coal power plants, a SOFC produces a higher electrical conversion efficiency. SOFC is a possible candidate for energy production. However, at higher temperatures (800-1000°C) it creates a lower ionic conductivity, which limits the SOFC. When lowering the temperature, the ohmic resistance increases, as a thin film. In our research a YSZ, layer will be produced from a fine dimple grain structure allowing high flow of O2 mobility. This mobility increases ionic conductivity and decreases ohmic loss. The goal of our research is to determine if the YSZ thin film synthesis lead to minimum ohmic resistance of the films at optimum film thickness. The method that is used is to test different molecular ratios of the YSZ and deposit the ratios with different energy levels onto different substrates, including conductors, semi-conductors, and insulators, and compare the properties of the YSZ layer. The thin films will be characterized through electrical measurements such as 4-Point Probe Resistivity measurements as well as AFM, SEM, and EDX Spectroscopy for the structural and compositional characterization. |
Tuesday, March 3, 2020 5:06PM - 5:18PM |
J52.00014: Time-resolved Nanosecond-Laser Recrystallization of Amorphous FeDy-O Thin Films in the (S)TEM Krishna Koirala, Chenze Liu, Tatiana Allen, Ramki Kalyanaraman, Gerd Duscher Iron-Dysprosium oxide thin film can be an amorphous semiconductor with unusual magneto-optic properties. The properties of amorphous materials are often governed by local structure and recrystallization mechanism is important for the stability of the materials system as well as engineering of properties. To investigate the structure and chemical composition of this material, we employed laser processing inside the (S)TEM with simultaneous High-Resolution Transmission Electron Microscopy (HRTEM) imaging, Electron Diffraction, and Electron Energy Loss Spectroscopy (EELS) measurements. It shows that the structural change in amorphous FeDy-O can be seen as early as with 100 ns single laser pulse at the laser fluency of 1.49E6 J/cm2 as indicated by the emergence of sharp diffraction rings from initial broad and diffuse diffraction ring. The pulsed laser-induced changes were studied up to 10,000 pulses where intense Brag’s spots were visible. Our results provide insight on unique way of understanding the local structure evolution and time resolution of the recrystallization process with laser pulses and allow us to conclude back onto the amorphous atomic arrangement of this material system. |
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J52.00015: Ionic liquid gate induced modifications of oxides surface Yuechen Zhuang, Bin Cui, Hao Yang, Fang Gao, Stuart Parkin Intense electric fields developed during gating at the interface between an ionic liquid (IL) and an oxide layer have been shown to lead to significant structural and electronic phase transitions in the entire oxide layer. An archetypical exampleis the reversible transformation between the brownmillerite SrCoO2.5 and the perovskite SrCoO3 engendered by ionic liquid gating. In this presentation, we show using in-situ atomic force microscopy studies, with photothermal excitation that allows for high quality measurements in the viscous environment of the ionic liquid, that the edges of atomically smooth terraces at the surface of SrCoO2.5 films are significantly modified by IL gating but that the terraces themselves remain smooth. The edges develop ridges that we show, using complementary X-ray photo emission spectroscopy studies, result from the adsorption of hydroxyl groups. Our findings open up opportunities for electrically controlled surface modifications in emergent ionitronic applications. |
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