A5038466981- Electronic and Structural Properties of Oxides
- Particle Detector Development and Performance
- Semiconductor materials and devices
- Electron and X-Ray Spectroscopy Techniques
- ZnO doping and properties
- Radiation Detection and Scintillator Technologies
- CCD and CMOS Imaging Sensors
- Magnetic properties of thin films
- X-ray Spectroscopy and Fluorescence Analysis
- Advanced Semiconductor Detectors and Materials
- Semiconductor materials and interfaces
- Catalytic Processes in Materials Science
- Advanced Photocatalysis Techniques
- Advanced X-ray Imaging Techniques
- Advanced X-ray and CT Imaging
- Nuclear Physics and Applications
- TiO2 Photocatalysis and Solar Cells
- Diamond and Carbon-based Materials Research
- Quantum Dots Synthesis And Properties
- High-Temperature Coating Behaviors
- Magnetic and transport properties of perovskites and related materials
- Advanced Optical Sensing Technologies
- Transition Metal Oxide Nanomaterials
- Gas Sensing Nanomaterials and Sensors
- Metal and Thin Film Mechanics
Brookhaven National Laboratory
2015-2024
National Synchrotron Light Source II
2009-2024
Brookhaven College
2017
National Institute of Standards and Technology
2010-2015
Bilkent University
2015
Hacettepe University
2015
IBM Research - Thomas J. Watson Research Center
2010-2012
Stony Brook University
2012
University of Delaware
2002-2010
Johns Hopkins University
2010
We have determined the electronic and atomic structure of N doped TiO2 using a combination hard x-ray photoelectron spectroscopy first-principles density functional theory calculations. Our results reveal that doping leads to formation oxygen vacancies both impurity accounts for observed visible light catalytic behavior TiO2.
We report stabilization of magnetic glassy state in non-stoichiometric nickel ferrite thin films prepared by pulse laser deposition. Details electronic structure the are presented and compared with stoichiometric bulk counterpart. Hard x-ray photoelectron spectroscopy shows significant amount oxygen vacancies enhanced cationic inversion for films. Films show spin glass (SG) features which is contrary to usual ferrimagnetic response ferrite. exhibit freezing temperature above room low fields...
Nickel ferrite thin films were synthesized by pulsed laser deposition. It was determined that the monotonic increase in saturation magnetization and non-monotonic electrical conductivity depend on oxygen partial pressure during growth of films. A substantial reduction found which ranged between 0.4% 40% bulk value as increased from 0.2 × 10 −6 Torr to 500 mTorr deposition There a three orders magnitude for sample prepared under most deficient environment (partial Torr). These variations are...
The use of $\alpha$-tantalum in superconducting circuits has enabled a considerable improvement the coherence time transmon qubits. standard approach to grow thin films on silicon involves heating substrate, which takes several hours per deposition and prevents integration this material with wafers containing temperature-sensitive components. We report detailed experimental study an alternative growth method silicon, is achieved at room temperature through niobium seed layer. Despite...
Recent applications of hard x-ray photoelectron spectroscopy (HAXPES) demonstrate its many capabilities in addition to several limitations. Examples are given, including measurement buried interfaces and materials under situ or operando conditions, as well measurements standing-wave resonant excitation. Physical considerations that differentiate HAXPES from photoemission utilizing soft ultraviolet photon sources also presented.
We report the crystallization study of CoFeB/MgO/CoFeB magnetic tunnel junctions using in-situ, time-resolved synchrotron-based x-ray diffraction and transmission electron microscopy. It was found that amorphous CoFeB electrodes occurs on a time scale seconds during postgrowth high temperature annealing. The can be well fit by Johnson–Mehl–Avrami model effective activation energy process determined to 150 kJ/mol. solid-state epitaxy mode involve separate at different locations followed...
We report the study of real-time evolution tunneling magnetoresistance (TMR) in CoFeB∕MgO∕CoFeB junctions during annealing at 380°C. The TMR quickly developed early stage annealing, with 200% observed less than 10min, followed by a slow approach to saturation. This was correlated structural changes, including crystallization amorphous CoFeB electrodes and improvement barrier quality annealing.
Abstract Data bandwidth, timing resolution and resource utilization in readouts of radiation detectors are a constant challenge. Event driven solutions pushing against well-trenched framed solutions. The idea for an asynchronous readout architecture called EDWARD ( E vent- D riven W ith A ccess R eset ecoder) was presented at the TWEPP 2021 conference. Here we show progress our work which resulted two chip prototypes. first one, named 3FI65P1, is full device with analog pixel circuitry...
Extended x-ray-absorption fine structure (EXAFS) was used to study the evolution of local Fe and Co as a function annealing time in CoFeB/MgO/CoFeB magnetic tunnel junctions. EXAFS indicates B depletion crystallization CoFeB layers within few seconds post growth high temperature anneal. The decrease first-shell Debye–Waller factor hence increase structural order during explains magnetoresistance observed result deposition annealing.
Hard x-ray photoelectron spectroscopy was applied to investigate the diamond-metal Schottky barrier heights for several metals and diamond surface terminations. The position of valence-band maximum determined by theoretically calculating density states applying cross section corrections. diamond-platinum height lowered 0.2 eV after thermal annealing, indicating annealing may increase carrier injection in devices leading photoconductive gain. platinum contacts on oxygen-terminated found...
We find a 5 eV satellite in the $\mathrm{Ti}\phantom{\rule{0.16em}{0ex}}1s$ photoelectron spectrum of transition-metal oxide $\mathrm{SrTi}{\mathrm{O}}_{3}$. This appears addition to well-studied 13 structure that is typically associated with $\mathrm{Ti}\phantom{\rule{0.16em}{0ex}}2p$ core line. give direct experimental evidence presence two satellites due crystal-field splitting metal $3d$ orbitals. They originate from ligand...
First-principles, real-time-cumulant, and Bethe-Salpeter-equation calculations fully capture the detailed satellite structure that occurs in response to sudden creation of core hole both photoemission x-ray absorption spectra transition-metal compounds $\mathrm{SrTi}{\mathrm{O}}_{3}$ rutile $\mathrm{Ti}{\mathrm{O}}_{2}$. Analysis excited-state, real-space charge-density fluctuations betrays physical nature these many electron excitations are shown reflect materials' solid-state electronic...
We report the hard x-ray photo-electron spectroscopy (HAXPES) and near edge absorption fine structure (NEXAFS) of CoFeB|MgO|CoFeB interfaces as a function annealing time. Upon annealing, oxidation state B changes from predominantly elemental (0 valence) boron in deposited sample to higher annealed samples evident HAXPES spectra. The NEXAFS results showed that upon heating, species migrate towards MgO interact with it. A comparison tunnel junction signature some standards suggests forms...
Hard x-ray photoelectron spectroscopy (HAXPES) and variable kinetic energy (VKE-XPS) analyses have been performed on ten-unit-cell-thick ${\mathrm{La}}_{(1\ensuremath{-}\ensuremath{\delta})}{\mathrm{Al}}_{(1+\ensuremath{\delta})}{\mathrm{O}}_{3}$ films, with La:Al ratios of 1.1, 1.0, 0.9, deposited ${\mathrm{SrTiO}}_{3}$. Only Al-rich films are known to a conductive interface. VKE-XPS, coupled maximum entropy analysis, shows significant differences in the compositional depth profile among...
Magnetic core/shell nanoparticles have been prepared using a method that is modified version of inert gas condensation (IGC) technique. Using resistive evaporation and laser ablation techniques combined in an IGC system, we shown it possible to synthesize nanostructures made different materials. Resistively evaporated Ni ablated CoO formed the particles. It has found these particles improved magnetic properties due their layered structures form as result oxidation core before gets coated by...
We report the effects on ferromagnetism due to co-doping of ZnO with Co and Cu in presence variable numbers oxygen vacancies. The co-doped nanoparticles Zn0.95−Co0.05CuyO (0.00≤y<0.009) were prepared via chemical route vacancies introduced annealing a reducing atmosphere for amounts time. In addition magnetization, particles characterized by x-ray diffraction (XRD), photoemission spectroscopy (XPS) absorption near edge (XANES). ions determined be +2 state tetrahedral symmetry, no evidence...
Hydrogen is among several energy sources that will be needed to replace the quickly diminishing fossil fuels. Free hydrogen not available naturally on earth and current processes require a fuel, methane, generate hydrogen. Electrochemical splitting of water titania proposed by Fujishima suffers from low efficiency. The efficiency could enhanced if full sun spectrum can utilized. Using pulsed laser deposition technique we synthesized nitrogen doped titanium dioxide (TiO2−xNx) thin films with...
We have investigated the structural and local atomic properties of Ge nanocrystals (Ge-ncs) embedded ZnO (ZnO: Ge) thin films. The films were deposited by sequential sputtering film layers on z-cut quartz substrates followed an ex-situ rapid thermal annealing (RTA) at 600 °C for 30, 60, 90 s under forming gas atmosphere. Effects RTA time evolution Ge-ncs x-ray diffraction (XRD), scanning electron microscopy (SEM), hard photoelectron spectroscopy (HAXPES), extended absorption fine structure...
We have constructed a pixelated germanium detector using technique which has been shown to provide good isolation between adjacent pixels. In this work we present initial tests of the application low-noise CMOS ASIC read out detector. The 64 pixels, each 0.5 mm×5 mm, arranged as series strips. It is connected by wire-bonds two 32-channel application-specific integrated circuits (ASICs) complete photon-counting chain for every channel. Since size pixel array no longer restricted difficulties...