A5045676731- Electronic and Structural Properties of Oxides
- ZnO doping and properties
- Magnetic and transport properties of perovskites and related materials
- Semiconductor materials and devices
- Copper-based nanomaterials and applications
- Ferroelectric and Piezoelectric Materials
- Electron and X-Ray Spectroscopy Techniques
- Multiferroics and related materials
- Iron oxide chemistry and applications
- Magnetic Properties and Synthesis of Ferrites
- Ga2O3 and related materials
- Catalytic Processes in Materials Science
- Transition Metal Oxide Nanomaterials
- Magnetic properties of thin films
- Advanced Condensed Matter Physics
- Advancements in Battery Materials
- X-ray Spectroscopy and Fluorescence Analysis
- Radioactive element chemistry and processing
- Surface and Thin Film Phenomena
- Shape Memory Alloy Transformations
- Chalcogenide Semiconductor Thin Films
- Nuclear Materials and Properties
- Advancements in Solid Oxide Fuel Cells
- Photocathodes and Microchannel Plates
- Gas Sensing Nanomaterials and Sensors
Pacific Northwest National Laboratory
2014-2024
Battelle
2006-2019
Physical Sciences (United States)
2014-2015
Wyle (United States)
2012
Wright State University
2012
United States Air Force Research Laboratory
2012
University of North Texas
2010
Environmental Molecular Sciences Laboratory
2001-2004
University of Wisconsin–Milwaukee
1994-1999
University of Wisconsin–Madison
1994-1997
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...
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...
We show that under certain conditions, highly Co-enriched TiO2 anatase clusters nucleate on epitaxial grown LaAlO3(001) by oxygen plasma assisted molecular beam epitaxy. In the most extreme cases, virtually all incident Co segregates to clusters, yielding a nanoscale ferromagnetic phase is not in homogeneous films of same concentration. The nucleation this simultaneous with continuous film growth must be carefully monitored order avoid drawing false conclusions about structure.
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...
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...
Abstract We describe the synthesis and characterization of high‐performance, superparamagnetic, iron oxide nanoparticle‐based, heavy metal sorbents, which demonstrate excellent affinity for separation metals in contaminated water systems (i.e., spiked Columbia River water). The magnetic nanoparticle sorbents were prepared from an easy‐to‐synthesize precursor, followed by a simple, one‐step ligand exchange reaction to introduce surface that is specific or class contaminants. engineered have...
There is a growing interest in knowing the sputter rates for wide variety of oxides because their increasing technological importance many different applications. To support needs users Environmental Molecular Sciences Laboratory, national scientific user facility, as well our research programs, authors made series measurements from oxide films that have been grown by oxygen plasma-assisted molecular beam epitaxy, pulsed laser deposition, atomic layer electrochemical oxidation, or...
A method for tuning the analyte affinity of magnetic, inorganic nanostructured sorbents heavy metal contaminants is described. The manganese-doped iron oxide nanoparticle have a remarkably high compared to precursor material. Sorbent can be tuned toward an interest simply by adjustment dopant quantity. results show that following Mn doping process there large increase in and capacity metals (i.e., Co, Ni, Zn, As, Ag, Cd, Hg, Tl). Capacity measurements were carried out removal cadmium from...
${\mathrm{LaAlO}}_{3}$ 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...
Core-level and valence-band x-ray photoemission spectra measured for molecular-beam-epitaxy-grown ${\mathrm{LaCrO}}_{3}/{\mathrm{SrTiO}}_{3}(001)$ yield band offsets potential gradients within the ${\mathrm{LaCrO}}_{3}$ sufficient to trigger an electronic reconstruction alleviate polarity mismatch. Yet, interface is insulating. Based on first principles calculations, we attribute this unexpected result interfacial cation mixing combined with charge redistribution ${\mathrm{CrO}}_{2}$ layers,...
MnBi has attracted much attention in recent years due to its potential as a rare-earth-free permanent magnet material. It is unique because coercivity increases with increasing temperature, which makes it good hard phase material for exchange coupling nanocomposite magnets. difficult obtain, partly the reaction between Mn and Bi peritectic, reacts readily oxygen. MnO formation irreversible harmful performance. In this paper, we report our efforts toward developing To date, high purity (>90%)...
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...
Over the past five years, considerable work has been carried out in exploration of candidate diluted oxide magnetic semiconductors with high Curie temperatures. Fueled by early experimental results and theoretical predictions, claims ferromagnetism at above room temperature doped oxides have abounded. In general, neither true nature these materials nor physical causes magnetism adequately determined. It is now apparent that dilute systems are deceptively complex. We consider two...
Ultrathin films of nickel exhibit an unusual sequence transitions from in-plane to perpendicular magnetization as a function film thickness. A sharp transition is found near 7 ML thickness, followed by gradual back beginning at 37 ML. This cannot be explained the surface or shape anisotropies, both which favor in thickness range where anisotropy found. We have measured dependence these for wedges, and capped nonmagnetic magnetic overlayers, experimentally determine surface, interface,...
Shewanella oneidensis MR-1 is purported to express outer membrane cytochromes (e.g., MtrC and OmcA) that transfer electrons directly Fe(III) in a mineral during anaerobic respiration. A prerequisite for this type of reaction would be the formation stable bond between cytochrome an iron oxide surface. Atomic force microscopy (AFM) was used detect whether specific forms hematite (Fe(2)O(3)) thin film, created with oxygen plasma-assisted molecular beam epitaxy, recombinant or OmcA molecules...
Metals deposited in vacuum on metal oxides such as alumina normally grow three-dimensional clusters because of weak adatom-substrate interactions. This tendency hinders our ability to form interfaces ultrathin, laminar films for use microelectronics and other technologies where nanostructural control is desired. We present experimental theoretical results showing that room temperature Co deposition fully hydroxylated clean sapphire (α-Al 2 O 3 ) produces a surface chemical reaction leads...
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,...
Cobalt-doped titanium dioxide, or CTO, has emerged in the past 2 years as a semiconducting, transparent, room-temperature ferromagnet. Very recently it been shown that magnetism CTO often originates surface nanoparticles Co-rich regions have much-enhanced substitutional Co content up to 40% of Ti sites, so magnetic is not true dilute semiconductor (DMS), but rather fairly high-density spin system. In this work we describe computational study using generalized gradient approximation density...
ABSTRACT Antibody recognition force microscopy showed that OmcA and MtrC are expressed on the exterior surface of living Shewanella oneidensis MR-1 cells when Fe(III), including solid-phase hematite (Fe 2 O 3 ), was terminal electron acceptor. localized to interface between cell mineral. displayed a more uniform distribution across surface. Both cytochromes were associated with an extracellular polymeric substance.
Stoichiometric epitaxial LaAlO(3) grown on TiO(2)-terminated SrTiO(3)(001) by off-axis pulsed laser deposition is shown to exhibit strong cation intermixing. This result corroborated classical and quantum mechanical calculations of the relative stabilities abrupt intermixed interface configurations. The valence band offset was measured be 0.16 ± 0.10 eV, this value cannot accounted for theoretically without including intermixing in physical description interface.
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...