A5007883299- Chalcogenide Semiconductor Thin Films
- Quantum Dots Synthesis And Properties
- Copper-based nanomaterials and applications
- Electron and X-Ray Spectroscopy Techniques
- X-ray Spectroscopy and Fluorescence Analysis
- Semiconductor materials and interfaces
- Advanced Chemical Physics Studies
- Silicon and Solar Cell Technologies
- Semiconductor materials and devices
- Advanced Photocatalysis Techniques
- X-ray Diffraction in Crystallography
- ZnO doping and properties
- Advanced Semiconductor Detectors and Materials
- Catalytic Processes in Materials Science
- Molecular Junctions and Nanostructures
- Crystallography and Radiation Phenomena
- Gas Sensing Nanomaterials and Sensors
- Electronic and Structural Properties of Oxides
- Organic Light-Emitting Diodes Research
- Electrocatalysts for Energy Conversion
- Semiconductor Quantum Structures and Devices
- Spectroscopy and Quantum Chemical Studies
- Machine Learning in Materials Science
- Advanced X-ray Imaging Techniques
- Organic Electronics and Photovoltaics
University of Nevada, Las Vegas
2016-2025
Karlsruhe Institute of Technology
2016-2025
Lawrence Berkeley National Laboratory
1997-2022
Georgia Institute of Technology
2022
Fraunhofer Institute for Chemical Technology
2022
University of Delaware
2022
University of Southern Denmark
2021
Virginia Tech
2019
University of Nevada, Reno
2012-2018
Binghamton University
2017
This work reports a facile method for preparing highly photoactive α-Fe(2)O(3) films as well their implementation photoanodes water oxidation. Transparent were prepared by new deposition-annealing (DA) process using nontoxic iron(III) chloride the Fe precursor, followed annealing at 550 °C in air. Ti-doped same method, with titanium butoxide added Ti precursor. Impedance measurements show that Ti-dopant serves an electron donor and increases density 2 orders of magnitude. The...
We have studied the electronic structure of liquid water using x-ray absorption spectroscopy at oxygen K edge. Since process takes less than a femtosecond, it allows probing molecular orbital frozen, local geometries molecules timescale that has not previously been accessible. Our results indicate is significantly different from solid and gaseous forms, resulting in pronounced pre-edge feature below main edge spectrum. Theoretical calculations these spectra suggest this originates specific...
By combining ultraviolet and x-ray photoelectron spectroscopy with inverse photoemission spectroscopy, we find that the conduction-band alignment at CdS/CuInSe2 thin-film solar-cell heterojunction is flat (0.0±0.2 eV). Furthermore, observe a valence-band offset of 0.8±0.2 eV. The electronic level dominated by (1) an unusually large surface band gap CuInSe2 thin film (1.4 eV), (2) reduced CdS overlayer (2.2 eV) due to intermixing effects, (3) general influence on chemical state near interface.
The electronic structure of the CdS/Cu2ZnSnS4 (CZTS) heterojunction was investigated by direct and inverse photoemission. effects a KCN etch CZTS absorber prior to CdS deposition on band alignment at respective interface were studied. We find “cliff”-like conduction offset CdS/CZTS independent pretreatment significant etch-induced enhancement energetic barrier for charge carrier recombination across interface.
High-resolution x-ray absorption and emission spectra of liquid water exhibit a strong isotope effect. Further, the show splitting $1{b}_{1}$ line, weak temperature effect, pronounced excitation-energy dependence. They can be described as superposition two independent contributions. By comparing with gas phase, ice, $\mathrm{NaOH}/\mathrm{NaOD}$, we propose that components are governed by initial state hydrogen bonding configuration ultrafast dissociation on time scale O $1s$ core hole decay.
Polycrystalline WO3 thin films for photoelectrochemical hydrogen production were investigated using photoelectron spectroscopy and inverse photoemission. First, we report on a careful study to minimize X-ray electron beam-induced degradation. Second, combined ultraviolet photoemission determine the surface positions of valence conduction band edges, respectively, work function (i.e., position vacuum level). This allows us paint completely experiment-based picture level positions, which are...
The substitution of rare metals such as iridium and platinum in light-emitting materials is a key step to enable low-cost mass-production organic diodes (OLEDs). Here, it demonstrated that using solution-processed, fully bridged dinuclear Cu(I)-complex can yield very high efficiencies. An optimized device gives maximum external quantum efficiency 23 ± 1% (73 2 cd A−1).
The valence band structures (VBS) of eight transition metals (Fe, Co, Ni, Cu, Pd, Ag, Pt, Au) were investigated by photoelectron spectroscopy (PES) using He I, II, and monochromatized Al Kα excitation. influence final states, photoionization cross-section, adsorption residual gas molecules in an ultrahigh vacuum environment are discussed terms their impact on the VBS. We find that VBSs recorded with radiation most closely comparable to ground state density states (DOS) derived from quantum...
An endstation with two high-efficiency soft x-ray spectrographs was developed at Beamline 8.0.1 of the Advanced Light Source, Lawrence Berkeley National Laboratory. The is capable performing absorption spectroscopy, emission and, in particular, resonant inelastic scattering (RIXS). Two slit-less variable line-spacing grating are installed different detection geometries. covers photon energy range from 80 to 1500 eV. For studying transition-metal oxides, large window allows a simultaneous...
A NaF/KF postdeposition treatment (PDT) has recently been employed to achieve new record efficiencies of Cu(In,Ga)Se2 (CIGSe) thin film solar cells. We have used a combination depth-dependent soft and hard X-ray photoelectron spectroscopy as well absorption emission gain detailed insight into the chemical structure CIGSe surface how it is changed by different PDTs. Alkali-free CIGSe, NaF-PDT NaF/KF-PDT absorbers grown low-temperature coevaporation interrogated. find that alkali-free surfaces...
Abstract Cu 2 ZnSnS 4 (CZTS) thin‐film solar cell absorbers with different bandgaps can be produced by parameter variation during thermal treatments. Here, the effects of varied annealing time in a sulfur atmosphere and an ordering treatment absorber are compared. Chemical changes surface due to examined, downshift valence band edge is observed. With goal obtain alignments, these CZTS combined Zn 1− x Sn O y (ZTO) or CdS buffer layers produce complete devices. A high open circuit voltage 809...
Interfacial engineering has fueled recent development of p-i-n perovskite solar cells (PSCs), with self-assembled monolayer-based hole-transport layers (SAM-HTLs) enabling almost lossless contacts for solution-processed PSCs, resulting in the highest achieved power conversion efficiency (PCE) to date. Substrate interfaces are particularly crucial growth and quality co-evaporated PSCs. However, adoption SAM-HTLs absorbers is complicated by underexplored interaction such perovskites phosphonic...
A detailed characterization of the impact a RbF post-deposition treatment (RbF-PDT) on chemical structure wide-gap Cu(In, Ga)Se2 thin-film solar cell absorber surface with high Ga/(Ga + In) (GGI) ratio 0.9 is presented. Using synchrotron- and lab-based x-ray photoelectron spectroscopy, as well x-ray-excited Auger electron we observe distinct differences to RbF-PDT surfaces common GGI ∼0.3. In particular, reduces sodium oxide content at surface, while copper concentration not affected. We...
The electronic structure of Alq3 is investigated using density functional theory-based calculations, photoemission and near-edge x-ray absorption fine structure. distinct features the observed spectra are understood in terms contributions from different atoms molecular orbitals. Fingerprints bonding individual identified. These results meant to be a reference for monitoring chemical processes that may undergo during fabrication or degradation light-emitting devices, understanding effects...
Decomposition of five amino acids, alanine, serine, cysteine, aspartic acid, and asparagine, under irradiation with soft X rays (magnesium Kalpha X-ray source) in ultra-high vacuum was studied by means photoelectron spectrometry (XPS) mass spectrometry. A comparative analysis changes XPS line shapes, stoichiometry residual gas composition indicates that the molecules decompose several pathways. Dehydration, decarboxylation, decarbonylation, deamination desulfurization pristine accompanied...
Quantum-confinement effects in the conduction band of deposited germanium nanocrystals are measured to be greater than similar-sized silicon nanocrystals. The particles condensed out gas phase and their electronic properties determined with x-ray absorption spectroscopy. edge shifts range from 0.2 eV for 2.7 nm up 1.1 1.2 particles.
A combination of x-ray emission spectroscopy and photoelectron using high brightness synchrotron radiation has been employed to investigate the electronic chemical structure buried CdS/Cu(In, Ga)Se2 interface, which is active interface in highly efficient thin film solar cells. In contrast conventional model an abrupt intermixing processes involving elements S, Se, have identified. The results shed light on formation semiconductor heterojunctions demonstrate a powerful tool for investigating...
The isotope effect and excitation-energy dependence have been measured in the oxygen K-edge x-ray emission spectrum (XES). use of XES to monitor core decay processes provides information about molecular dynamics (MD) on an ultrafast time scale through O1s lifetime a few femtoseconds. Different nuclear masses give rise differences observed is direct evidence importance such processes. MD simulations show that even mainly related core-excited-state dynamics.
To facilitate a less empirical approach to developing improved catalysts, it is important correlate catalytic performance surrogate properties that can be measured or predicted accurately and quickly, allowing experimental synthesis testing of catalysts focus on the most promising cases. Particularly hopeful correlating catalysis electronic density states (DOS). Indeed, there has been success in using just center d-electron density, which some cases correlates linearly with oxygen atom...
Recently, a world-record efficiency of 22.6% was achieved by applying RbF postdeposition treatment (PDT) on Cu(In,Ga)Se2 (CIGSe) thin-film solar cell absorber surface. Here, we study the impact this RbF-PDT electronic structure CIGSe surface and CdS/CIGSe interface using ultraviolet X-ray photoelectron spectroscopy (UPS XPS), as well inverse photoemission (IPES). After RbF-PDT, find small downward shift band edges, while gap value itself is not affected. In addition, further bending in...
The electronic structure of gas-phase H(2)O and D(2)O molecules has been investigated using resonant inelastic soft x-ray scattering (RIXS). We observe spectator shifts for all valence orbitals when exciting into the lowest three absorption resonances. Strong changes relative orbital emission intensities are found different resonances, which can be related to angular anisotropy RIXS process. Furthermore, excitation 4a(1) resonance leads nuclear dynamics on time scale process; we find...
The pristine state and soft X-ray induced decomposition of two aromatic amino acids, viz. phenylalanine tyrosine, have been studied by means XPS NEXAFS. spectroscopic data on radiation supplemented a mass spectral analysis the desorbed species. Despite very similar chemical structures, acids show dramatically different behavior toward ionizing radiation: degrades quickly whereas tyrosine shows prominent stability against damage. Reasons for this difference are discussed in relation to...
The band alignment at the CdS∕Cu(In,Ga)S2 interface in thin-film solar cells on a stainless steel substrate was investigated using photoelectron spectroscopy and inverse photoemission. By combining both techniques, conduction valence offsets were independently determined. We find an unfavorable offset of −0.45 (±0.15) eV, accounting for generally observed low open-circuit voltage indicating great importance buffer∕absorber such devices. surface gap Cu(In,Ga)S2 absorber is 1.76 being...
We present a variable line-space grating spectrometer for soft x-rays that covers the photon energy range between 130 and 650 eV. The optical design is based on Hettrick–Underwood principle tailored to synchrotron-based studies of radiation-sensitive biological samples. able record entire spectral in one shot, i.e., without any mechanical motion, at resolving power 1200 or better. Despite its slitless design, such can be achieved source spot as large (30×3000) μm2, which important keeping...