A5042725190- Electronic and Structural Properties of Oxides
- Magnetic and transport properties of perovskites and related materials
- ZnO doping and properties
- Copper-based nanomaterials and applications
- Nuclear materials and radiation effects
- Advancements in Solid Oxide Fuel Cells
- Semiconductor materials and devices
- Nuclear Materials and Properties
- Iron oxide chemistry and applications
- Ferroelectric and Piezoelectric Materials
- Advanced Materials Characterization Techniques
- Fusion materials and technologies
- Advanced Condensed Matter Physics
- Ga2O3 and related materials
- Electron and X-Ray Spectroscopy Techniques
- Radioactive element chemistry and processing
- Magnetic Properties and Synthesis of Ferrites
- Seismic Waves and Analysis
- Multiferroics and related materials
- Catalytic Processes in Materials Science
- Chalcogenide Semiconductor Thin Films
- Metal and Thin Film Mechanics
- Luminescence Properties of Advanced Materials
- Transition Metal Oxide Nanomaterials
- Gas Sensing Nanomaterials and Sensors
Pacific Northwest National Laboratory
2016-2025
Physical Sciences (United States)
2015-2023
Battelle
2015-2020
Richland College
2016
Environmental Molecular Sciences Laboratory
2009-2012
University of North Texas
2010
University of Washington
2003
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...
We report element specific structural and magnetic investigations on ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{O}$ epitaxial films using synchrotron radiation. Co dopants exclusively occupy Zn sites as revealed by x-ray linear dichroism having an unprecedented degree of perfection. Comparative field dependent measurements circular conventional magnetometry consistently show purely paramagnetic behavior for isolated dopant atoms with a moment $4.8{\ensuremath{\mu}}_{B}$....
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...
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...
Copper thiocyanate (CuSCN) is a candidate as transparent solid p-type conductor for optoelectronic and photovoltaic applications, such solar cells. We calculate the band structure, bonding characteristics, basic native defect configurations of hexagonal β-CuSCN. β-CuSCN predicted to be an indirect-gap semiconductor with unusual orbital character: although highest valence bands have expected character Cu 3d levels hybridized S 3p states, conduction minimum (at K point Brillouin zone) has...
${\mathrm{LaAlO}}_{3}$ 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...
Strontium-doped lanthanum cobalt ferrite (LSCF) is a widely used cathode material due to its high electronic and ionic conductivity, reasonable oxygen surface exchange coefficient. However, LSCF can have long-term stability issues such as segregation of Sr during solid oxide fuel cell (SOFC) operation, which adversely affect the electrochemical performance. Thus, understanding nature phenomenon how it affected by composition strain are critical. In this research, heteroepitaxial thin films...
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...
Thin film deposition is a fundamental technology for the discovery, optimization, and manufacturing of functional materials. Deposition by molecular beam epitaxy (MBE) typically employs reflection high-energy electron diffraction (RHEED) as real-time in situ probe growing film. However, state-of-the-art RHEED analysis during requires human observation. Here, we present an approach using machine learning (ML) methods to monitor, analyze, interpret images on-the-fly thin deposition. In...
We reexamine the mechanism of ferromagnetism in doped TiO(2) anatase, using epitaxial Cr:TiO(2) with excellent structural quality as a model system. In contrast to highly oriented but defective (approximately 0.5 micro(b)/Cr), these structurally superior single crystal films exhibit negligible ferromagnetism. Similar results were obtained for Co:TiO(2). show first time that charge-compensating oxygen vacancies alone, predicted by F-center mediated exchange, are not sufficient activate...
Epitaxial thin films of cobalt-doped ZnO (Co : ZnO) were deposited by pulsed laser deposition (PLD) on both c-plane and r-plane sapphire (Al2 O3). The exhibited high structural quality with narrow x-ray diffraction (XRD) rocking curve peak widths. X-ray absorption spectroscopy (XANES EXAFS) confirmed well-ordered Co substitution for Zn in without the formation secondary phases. A wide range n-type conductivities (10−4–105 Ω cm) was achieved controlling conditions, post-annealing vacuum,...
The use of synchrotron-based spectroscopy has revolutionized the way we look at matter. X-ray absorption (XAS) using linear and circular polarized light offers a powerful toolbox element-specific structural, electronic magnetic probes that is especially well suited for complex materials containing several elements. We specific example Zn1−xCoxO (Co:ZnO) to demonstrate usefulness combining these XAS techniques unravel its intrinsic properties. as long phase separation or excessive defect...
The electrical transport properties for compositionally and structurally well-defined epitaxial \ensuremath{\alpha}-(Ti${}_{x}$Fe${}_{1\ensuremath{-}x}$)${}_{2}$O${}_{3}$(0001) films have been investigated $x$ \ensuremath{\le} 0.09. All were grown by oxygen plasma-assisted molecular beam epitaxy using two different growth rates: 0.05--0.06 \AA{}/s 0.22--0.24 \AA{}/s. Despite no detectable difference in cation valence structural properties, at the lower rate highly resistive whereas those...
Rare earth nickelates including LaNiO3 are promising catalysts for water electrolysis to produce oxygen gas. Recent studies report that Fe substitution Ni can significantly enhance the evolution reaction (OER) activity of LaNiO3. However, role in increasing remains ambiguous, with potential origins both structural and electronic nature. On basis a series epitaxial LaNi1–xFexO3 thin films synthesized by molecular beam epitaxy, we tunes oxidation state volcano-like OER trend is observed, x =...
Abstract Radioactive waste immobilization is a means to limit the release of radionuclides from various streams into environment over timescale hundreds many thousands years. Incorporation radionuclide-containing wastes borosilicate glass during vitrification one potential route accomplish such immobilization. To facilitate comparisons and assessments reproducibility across experiments laboratories, six-component (Si, B, Na, Al, Ca, Zr) known as International Simple Glass (ISG) was developed...
The materials and magnetic properties of Cr-doped anatase ${\mathrm{TiO}}_{2}$ thin films deposited on ${\mathrm{LaAlO}}_{3}(001)$ ${\mathrm{SrTiO}}_{3}(001)$ substrates by oxygen-plasma-assisted molecular beam epitaxy have been studied in detail to elucidate the origin ferromagnetic ordering. Cr substitution for Ti lattice, with no evidence interstitials, segregation, or secondary phases, was independently confirmed transmission electron microscopy energy dispersive x-ray spectroscopy,...
X-ray absorption fine-structure (XAFS) measurements have been used to characterize a series of Co-doped ZnO films grown on sapphire substrates by pulsed laser deposition. The emphasis is characterization the fate Co dopant: metallic particles or substitutional $\text{Co}2+$. It shown that analysis both near edge and extended fine structure can provide measurement fraction Co. Any quantitative understanding magnetism in this system needs take into account types Results are reported for two...
Understanding the structure of well-defined anatase TiO2 surfaces is critical for deciphering site-specific thermal and photoreaction mechanisms on TiO2. Using ultrahigh vacuum scanning tunneling microscopy (STM), we have studied atomic TiO2(001) epitaxial thin films grown by oxygen plasma assisted molecular beam epitaxy. Bright rows (1×4) reconstructed surface are resolved as three types features with different sizes. High-resolution STM images taken from same area at bias voltages show...
Strain confinement in heterostructured films significantly affects ionic conductivity of the electrolytes for solid oxide fuel cells based on a multi-layered design strategy. Nearly ideal tensile strain can be achieved by dedicated manipulation lattice mismatch between adjacent layers and fine control layer thicknesses to minimize formation dislocations thus achieve optimized conduction. This strategy was demonstrated model system multilayered 8 mol%Y(2)O(3) stabilized ZrO(2) (YSZ) with...
We have investigated the electronic and optical properties of epitaxial La1-xSrxFeO3 for x from 0 to 1 prepared by molecular beam epitaxy. Core-level valence-band x-ray photoemission features monotonically shift lower binding energy with increasing x, indicating downward movement Fermi level toward valence band maximum. Both Fe 2p O 1s spectra broaden higher consistent delocalization Sr-induced holes in 3d/O hybridized band. Combining X-ray K-edge absorption data, we map evolution occupied...
Abstract Oxide heterointerfaces are extremely common in both natural and artificial composite structures, including corroded structural materials. Often, key properties such as segregation atomic transport dictated by the structure of these interfaces. However, despite this critical link, very few have been studied any detail at scale. Here, one important oxide heterointerface is examined, between spinel corundum, using chemical system FeCr 2 O 4 /Cr 3 a representative technologically case....