A5085194675- Electronic and Structural Properties of Oxides
- Magnetic and transport properties of perovskites and related materials
- Semiconductor materials and devices
- ZnO doping and properties
- Electron and X-Ray Spectroscopy Techniques
- Ferroelectric and Piezoelectric Materials
- Iron oxide chemistry and applications
- Catalytic Processes in Materials Science
- Copper-based nanomaterials and applications
- Advanced Condensed Matter Physics
- Multiferroics and related materials
- Magnetic Properties and Synthesis of Ferrites
- Ga2O3 and related materials
- Magnetic properties of thin films
- Advanced Photocatalysis Techniques
- Catalysis and Oxidation Reactions
- Advanced Chemical Physics Studies
- Surface and Thin Film Phenomena
- Transition Metal Oxide Nanomaterials
- Advancements in Solid Oxide Fuel Cells
- X-ray Spectroscopy and Fluorescence Analysis
- Electrocatalysts for Energy Conversion
- TiO2 Photocatalysis and Solar Cells
- Gas Sensing Nanomaterials and Sensors
- Ferroelectric and Negative Capacitance Devices
Pacific Northwest National Laboratory
2016-2025
Computational Sciences (United States)
2025
Physical Sciences (United States)
2015-2024
Environmental Molecular Sciences Laboratory
2000-2020
Battelle
2000-2019
Richland College
2015-2018
Nanyang Technological University
2018
University of Minnesota
1986-2015
Tohoku University
2010
University of North Texas
2010
We have used oxygen-plasma-assisted molecular-beam epitaxy (OPA-MBE) to grow CoxTi1−xO2 anatase on SrTiO3(001) for x=∼0.01–0.10, and measured the structural, compositional, magnetic properties of resulting films. Whether epitaxial or polycrystalline, these films are ferromagnetic semiconductors at above room temperature. However, structural depend critically Co distribution, which varies widely with growth conditions. is substitutional in lattice +2 formal oxidation state CoxTi1−xO2. The...
Abstract Perovskite‐structured (ABO 3 ) transition metal oxides are promising bifunctional electrocatalysts for efficient oxygen evolution reaction (OER) and reduction (ORR). In this paper, a set of epitaxial rare‐earth nickelates (RNiO thin films is investigated with controlled A‐site isovalent substitution to correlate their structure physical properties ORR/OER activities, examined by using three‐electrode system in O 2 ‐saturated 0.1 m KOH electrolyte. The ORR activity decreases...
The hypothesis that high-Curie-temperature ferromagnetism in cobalt-doped ZnO (Co2+: ZnO) is mediated by charge carriers was tested controlled introduction and removal of the shallow donor interstitial zinc. Using oriented epitaxial Co2+: films grown chemical vapor deposition, kinetics measurements demonstrate a direct correlation between oxidative quenching diffusion oxidation These results systematic variation key parameter involved and, process, unambiguously reveal this to be dependent...
We address the issue of accurate determination valence band maximum (VBM) for SrTiO3(001) single crystals and epitaxial films, as well TiO2(001) anatase SrO films. These measurements are critical importance in determining offsets heterojunctions these oxides with Si. Three different methods analyzed: (1) fitting a Gaussian broadened theoretical density states to x-ray photoelectron spectrum; (2) finding intersection regression line that spans linear portion leading edge background between...
X-ray photoemission experiments were carried out to study the reaction of water vapor with clean (0001) surfaces single-crystal corundum (α-Al2O3) and single-crystal, thin-film hematite (α-Fe2O3) at constant time (3 min) as a function pressure [p(H2O)] and, in separate experiments, longer times (=30 min, total exposure ranging from 1.8 L 1.8×1010 L) p(H2O). A two-stage was observed for each oxide surface, dissociative chemisorption occurring mainly defect sites below threshold pressures ≈1...
Abstract We review recent work in the application of Auger and X-ray photoelectron diffraction at high electron kinetic energies to problem structure determination ultrathin epitaxial overlayers. These closely-related techniques are based on fact that outgoing photoelectrons from single-crystal specimens undergo elastic scattering interference near-neighbour atoms vicinity emitter. Such coherent leads large intensity modulations as detected emission direction is varied with respect crystal...
Colloidal cobalt-doped TiO2 (anatase) nanocrystals were synthesized and studied by electronic absorption, magnetic circular dichroism, transmission electron microscopy, susceptibility, cobalt K-shell X-ray absorption spectroscopy, extended fine structure measurements. The paramagnetic when isolated surface-passivating ligands, weakly ferromagnetic (Ms ≈ 1.5 × 10-3 μB/Co2+ at 300 K) aggregated, strongly (up to Ms = 1.9 spin-coated into nanocrystalline films. data reveal that is in the Co2+...
In situ X-ray photoelectron spectroscopy (XPS) was utilized to identify the chemical state of silver in a range oxide thin films obtained by codeposition and atomic oxygen. A highly oxidized species observed at an unexpectedly low Ag 3d5/2 binding energy (BE) 366.8 eV with associated broad satellite 368.2 eV; this assigned as Ag(III). It found be unstable vacuum but could regenerated further exposure Both BE shifts intensity changes O 1s peak were correlate oxidation state. The theoretical...
Femtosecond transient reflectivity and absorption are used to measure the carrier lifetimes in α-Fe2O3 thin films single crystals. The results from show that initially excited hot electrons relax band edge within 300fs then recombine with holes or trap 5ps. trapped have a lifetime of hundreds picoseconds. Transient measurements hematite (α-Fe2O3) crystals similar but slightly faster dynamics leading conclusion short these materials due primarily trapping Fe d-d states gap. In crystal,...
$\mathrm{Co}$-doped $\mathrm{ZnO}({\mathrm{Co}}_{x}{\mathrm{Zn}}_{1\ensuremath{-}x}\mathrm{O})$ is of potential interest for spintronics due to the prediction room-temperature ferromagnetism. We have grown epitaxial ${\mathrm{Co}}_{x}{\mathrm{Zn}}_{1\ensuremath{-}x}\mathrm{O}$ films on ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}(012)$ substrates by metalorganic chemical vapor deposition using a liquid precursor delivery system. High concentrations $\mathrm{Co}(x\ensuremath{\leqslant}0.35)$ can be...
Epitaxial La1-x Srx CrO3 deposited on SrTiO3 (001) is shown to be a p-type transparent conducting oxide with competitive figures of merit and cubic perovskite structure, facilitating integration into electronics. Holes in the Cr 3d t2g bands play critical role enhancing conductivity, while transparency visible light maintained because low-lying d-d transitions arising from hole doping are dipole forbidden.
Abstract Photoemission electron microscopy (PEEM) excited by X‐ray and UV sources is used to investigate epitaxial anatase thin films with embedded rutile nanocrystals, a model system for the study of heterocatalysis on mixed‐phase TiO 2 . Both excitation show distinct contrast between two phases; however, reversed. Rutile nanocrystals appear darker than film in PEEM images but brighter UV‐PEEM images. We observe that topography‐induced dominant imaging, whereas work function...
The origin of ferromagnetism is investigated in epitaxial Co:ZnO thin films which become weakly ferromagnetic after annealing Zn vapor. Conventional characterization techniques indicate no change treatment. However, x-ray photoelectron spectroscopy depth profiling clearly indicates the presence Co(0) Zn-treated films; absorption fine structure utilized to identify secondary phase as CoZn. This work demonstrates that potential for phases must be thoroughly discounted, through painstaking...
${\mathrm{LaAlO}}_{3}$ epitaxial films with La:Al cation ratios ranging from 0.9 to 1.2 were grown on ${\mathrm{TiO}}_{2}$-terminated ${\mathrm{SrTiO}}_{3}$ (001) substrates by off-axis pulsed laser deposition. Although all are epitaxial, rocking curve measurements show that the crystallographic quality degrades increasing ratio. Films of 0.9, 1.0, and 1.1 coherently strained substrate. However, out-of-plane lattice parameter increases over this range, revealing a decrease in film...
We have spectroscopically determined the optical bandgaps and band offsets at epitaxial interfaces of BaSnO3 with SrTiO3(001) LaAlO3(001). 28 u.c. films exhibit direct indirect 3.56 ± 0.05 eV 2.93 eV, respectively. The lack a significant Burstein-Moss shift corroborates highly insulating, defect-free nature films. conduction minimum is lower in electron energy 5 than SrTiO3 LaAlO3 by 0.4 0.2 3.7 This result bodes well for realization oxide-based, high-mobility, two-dimensional systems that...
Abstract The perovskite oxide LaNiO 3 is a promising oxygen electrocatalyst for renewable energy storage and conversion technologies. Here, it shown that strontium substitution lanthanum in coherently strained, epitaxial films (La 1− x Sr NiO ) significantly enhances the evolution reaction (OER) activity, resulting performance at = 0.5 comparable to state‐of‐the‐art catalyst Ba Co 0.8 Fe 0.2 O 3− δ . By combining X‐ray photoemission absorption spectroscopies with density functional theory,...
Abstract The oxygen evolution reaction (OER) is a crucial process in electrochemical water splitting, promising technology to renewably yield hydrogen gas from water. Designing and developing earth‐abundant, efficient, stable OER electrocatalysts replace the most widely used but scarce RuO 2 IrO are thus of critical interest. Recently, ABO 3 ‐structured perovskite oxides, especially rare‐earth nickelates, extensively studied for their potential use as electrocatalysts. In particular,...
The surface structure of anatase ${\mathrm{TiO}}_{2}(001)$ was investigated using scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), reflection high-energy electron diffraction (RHEED), and low-energy (LEED). A two-domain $(1\ifmmode\times\else\texttimes\fi{}4)/(4\ifmmode\times\else\texttimes\fi{}1)$ reconstruction, similar to those previously reported in LEED ion scattering studies, observed by STM RHEED. This reconstruction found be stable not only from room...