A5087967722- Electron and X-Ray Spectroscopy Techniques
- X-ray Spectroscopy and Fluorescence Analysis
- Advanced Chemical Physics Studies
- Crystallography and Radiation Phenomena
- Electronic and Structural Properties of Oxides
- Advanced Electron Microscopy Techniques and Applications
- Magnetic properties of thin films
- Surface and Thin Film Phenomena
- Advanced X-ray Imaging Techniques
- Magnetic and transport properties of perovskites and related materials
- Semiconductor materials and devices
- X-ray Diffraction in Crystallography
- Advanced Condensed Matter Physics
- ZnO doping and properties
- Ion-surface interactions and analysis
- Advancements in Photolithography Techniques
- Photocathodes and Microchannel Plates
- Iron oxide chemistry and applications
- Advanced Materials Characterization Techniques
- Physics of Superconductivity and Magnetism
- Ga2O3 and related materials
- Rare-earth and actinide compounds
- Machine Learning in Materials Science
- Nuclear Physics and Applications
- Atomic and Molecular Physics
Lawrence Berkeley National Laboratory
2012-2023
University of California, Davis
2012-2023
Material Sciences (United States)
1999-2018
University of California, Berkeley
1971-2011
University of California System
2009
Forschungszentrum Jülich
2008
Universität Hamburg
2008
IBM Research - Almaden
2008
Technical University of Munich
2005
Lawrence Livermore National Laboratory
2004
Semiconductor heterostructures are the fundamental platform for many important device applications such as lasers, light-emitting diodes, solar cells, and high-electron-mobility transistors. Analogous to traditional heterostructures, layered transition metal dichalcogenide can be designed built by assembling individual single layers into functional multilayer structures, but in principle with atomically sharp interfaces, no interdiffusion of atoms, digitally controlled components, lattice...
A high pressure photoemission system is described that combines differential pumping with an electrostatic lens system. This approach allows optimized without loss of signal, thereby increasing the high-pressure performance by at least 2 orders magnitude compared to passive systems. general analysis aperture-based presented, followed a description prototype which has operated pressures up 7 mbar on synchrotron beamline. Using this approach, experiments should be possible 100 mbar. Example...
X-ray photoelectron spectroscopy (XPS) is used to measure splittings of metal-atom electron binding energies in both inorganic solids and gases. These are due the various possible multiplet states formed by coupling a hole subshell an unfilled valence subshell. Splittings observed containing $3d$-series atoms. In particular, $3s$ energy split into doublet with as much 7.0-eV separation between two components. The instrumental resolution \ensuremath{\sim} 1.0 eV. exhibited compounds Mn Fe,...
X-ray photoelectron spectra indicate core-electron binding-energy splittings of \ensuremath{\sim}6 eV for the $3s$ levels in Mn${\mathrm{F}}_{2}$, MnO, and Fe${\mathrm{F}}_{3}$, less pronounced effects on Mn${\mathrm{O}}_{2}$ Fe metal. These are considerably reduced from free-ion predictions but agree well with calculations Mn a cluster environment. The $3p$ multiplet shown to behave quantitatively different fashion.
Multiple-energy x-ray holography (MEXH) is employed to image the local atomic environment of Fe atoms in hematite. MEXH utilizes synchrotron radiation generate an interference field within sample, and then determines strength this near at specific sites from integrated fluorescence yield. Scanning extended volume reciprocal space, structure F${\mathrm{e}}_{2}$${\mathrm{O}}_{3}$ reconstructed by Fourier transformation hologram. Image aberrations known distort single-energy holograms are...
A theoretical and experimental study was made of the shift in atomic core-electron binding energies caused by chemical environment. Two models are presented to account for these “chemical shifts.” The first uses an energy cycle break into a free-ion contribution classical Madelung contribution. contributes significant part binding-energy shift. It can, principle, be evaluated rigorously although there is some ambiguity as surface correction. reference level must also considered comparing...
We address the century-old puzzle of existence a liquid-like layer at ice surface near its melting point with new photoelectron spectroscopic tools using synchrotron radiation. Near-edge x-ray absorption shows that film exists temperatures as low -20 °C. Near 0 °C this is about 20 Å thick, i.e., six bilayers. With high-pressure spectroscopy, we have further investigated effect contamination, which ubiquitous in natural environments, on state ice. Our results show premelting can be strongly...
The x-ray photoelectron intensity of the $1s$ core level adsorbed oxygen in form a $c(2\ifmmode\times\else\texttimes\fi{}2)$ overlayer on Cu (001) exhibits strong angular dependence due to final-state diffraction at low electron take-off angles. azimuthal anisotropies intensity, measured as $\frac{({I}_{max}\ensuremath{-}{I}_{min})}{{I}_{max}}$, are 24%, 23%, 16%, 13%, and 18% for scans fixed angles 7\ifmmode^\circ\else\textdegree\fi{}, 10\ifmmode^\circ\else\textdegree\fi{},...
The use of core-level photoelectron diffraction for structural studies surfaces and epitaxial overlayers is discussed. Photoelectron found to provide several direct rather unique types information, including the sites positions adsorbed atoms; orientations small molecules or fragments bound surfaces; orientations, layer thicknesses, vertical lattice constants, degrees short-range order partially-epitaxial overlayers; presence spin in magnetic materials. Specific systems considered are...
In x-ray photoelectron spectroscopy (XPS), a sample is exposed to low energy x rays (approximately 1 keV), and the resultant photoelectrons are analyzed with high precision for kinetic energy. After correction inelastic scattering, measured spectrum should reflect valence band density of states, as well binding energies several core electronic levels. All features in this will be modulated by appropriate photoelectric cross sections, there types final-state effects which could complicate...
A method for the simulation of electron scattering and diffraction in solids molecules within cluster approach is presented with explicit applications to photoelectron diffraction, molecules, low-energy diffraction. No approximations are made beyond muffin-tin model, and, particular, an exact representation free-electron Green function used. All multiple-scattering paths accounted up order that ensures convergence. The relies upon a convenient separation rotation matrices translations along...
We have measured the angular distributions of 1s photoelectrons excited by circularly and linearly polarized light from fixed-in-space CO N2 molecules, in vicinity their shape resonances. A strong circular dichroism, i.e., a dependence on sense rotation polarization vector photons, is found for both molecules. State-of-the-art one-electron multiple scattering partially correlated random phase approximation calculations are good agreement with many, but not all, aspects experimental data.
Abstract Over the last 10 years, a new technique for measuring electron binding energies has been developed by Siegbahn and co-workers at Uppsala [l] .
Stoichiometric FeRh undergoes a temperature-induced antiferromagnetic (AFM) to ferromagnetic (FM) transition at $\ensuremath{\sim}350\text{ }\text{ }\mathrm{K}$. In this Letter, changes in the electronic structure accompanying are investigated epitaxial thin films via bulk-sensitive valence-band and core-level hard x-ray photoelectron spectroscopy with photon energy of 5.95 keV. Clear differences between AFM FM states observed across entire spectrum these well reproduced using...
We present a theory of temperature-dependent photoemission which accurately describes phonon effects in soft and hard x-ray angle-resolved photoemission. Our approach is based on fully relativistic one-step that quantitatively reproduces the phonon-assisted transitions beyond usual $\mathbf{k}$-conserving dipole selection rules lead to so-called XPS limit and/or high temperature regime. Vibrational atomic displacements have been included using coherent potential approximation analogy...
The interfaces between two condensed phases often exhibit emergent physical properties that can lead to new physics and novel device applications are the subject of intense study in many disciplines. We here apply experimental theoretical techniques characterization one such interesting interface system: two-dimensional electron gas (2DEG) formed multilayers consisting $\mathrm{SrTi}{\mathrm{O}}_{3}$ (STO) $\mathrm{GdTi}{\mathrm{O}}_{3}$ (GTO). This system has been multiple studies recently...