Extended X-ray absorption fine structure

About: Extended X-ray absorption fine structure is a research topic. Over the lifetime, 10452 publications have been published within this topic receiving 276744 citations.

Physiochemical Investigation of Shape-Designed MnO2 Nanostructures and Their Influence on Oxygen Reduction Reaction Activity in Alkaline Solution

Abstract: In this work, five types of MnO2 nanostructres (nanowires, nanotubes, nanoparticles, nanorods, and nanoflowers) were synthesized with a fine control over their α-crystallographic form by hydrothermal method. The electrocatalytic activities of these materials were examined toward oxygen reduction reaction (ORR) in alkaline medium. Numerous characterizations were correlated with the observed activity by analyzing their crystal structure (TGA, XRD, TEM), material morphology (FE-SEM), porosity (BET), inherent structural nature (IR, Raman, ESR), surfaces (XPS), and electrochemical properties (Tafel, Koutecky–Levich plots and % of H2O2 produced). Moreover, X-ray absorption near-edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS) analysis were employed to study the structural information on the MnO2 coordination number as well as interatomic distance. These combined results show that the electrocatalytic activities are significantly dependent on the nanoshapes and follow an order nano...

Synchrotron Radiation: Techniques and Applications

Abstract: 1. Introduction - Properties of Synchrotron Radiation.- 1.1 Historical Development.- 1.2 Quantitative Properties.- 1.2.1 Equations for Ideal Orbits.- 1.2.2 Considerations for Real Orbits.- a) Coherence.- b) Periodic Wigglers.- c) Synchrotron Accelerators.- d) Beam Cross Section and Divergency.- 1.2.3 Time Structure.- 1.3 Comparison with other Sources.- 1.3.1 Infrared and Visible Range.- 1.3.2 Vacuum Ultraviolet Range.- 1.3.3 X-rays.- 1.4 Acknowledgments.- References.- 2. The Synchrotron Radiation Source.- 2.1 Fundamental Concepts.- 2.1.1 Orbit Dynamics.- a) Betatron Oscillations.- b) Betatron Oscillations of Off-energy Particles.- c) Phase Focusing and Synchrotron Oscillations.- 2.1.2 Radiation Damping.- 2.1.3 Beam Lifetime.- 2.1.4 Beam Cross Section.- 2.2 Design Considerations.- 2.2.1 Magnetic Field and Energy.- 2.2.2 Lattice.- 2.2.3 Injector.- 2.2.4 Accelerating System.- 2.2.5 Energy Shifter Wigglers.- 2.2.6 Multipole Wigglers (Undulator).- 2.3. Design Examples.- 2.3.1 Aladdin.- a) Lattice.- b) Vacuum System.- c) Accelerating System.- d) Injector.- e) Computer Control.- 2.3.2 The National Synchrotron Light Source (NSLS).- References.- 3. Instrumentation for Spectroscopy and other Applications.- 3.1 Layout and Operation of Laboratories.- 3.1.1 VUV Laboratory at a Small Storage Ring.- 3.1.2 VUV and X-Ray Laboratory at a Large Storage Ring.- 3.1.3 Beam Line Optics.- a) General Considerations.- b) The Phase Space Method.- c) Magic Mirrors.- 3.2 Optical Components.- 3.2.1 Mirrors and Reflective Coatings.- a) General Remarks.- b) Reflectivity in the Vacuum Ultraviolett.- c) Coating Materials and Multilayer Coatings.- d)Sattering and Stray Light.- e) Mirror Substrate Materials.- f) Imaging in VUV.- 3.2.2 Dispersive Elements.- a) Reflection Grating Dispersors.- b) Spherical Concave Gratings.- c) Aspherical Concave Gratings.- d) Efficiency and Blaze.- e) Holographic Gratings.- f) Zone Plates and Transmission Gratings.- g) Crystals for Monochromators.- 3.2.3 Filters and Polarizers.- a) Filters and higher Order Problems.- b) Polarizers.- 3.3 VUV Monochromators.- 3.3.1 General Considerations.- 3.3.2 Normal Incidence Monochromators.- 3.3.3 Grazing Incidence Monochromators.- a) Plane Grating Monochromators.- b) Rowland Mountings.- c) Non-Rowland Monochromators.- 3.3.4 New Concepts.- 3.4 X-Ray Monochromators.- 3.4.1 Plane Crystal Instruments.- 3.4.2 Higher Order Rejection.- 3.4.3 Bent Crystal Monochromators.- 3.5 Photon Detectors.- 3.5.1 Detectors for the Vacuum Ultraviolet.- 3.5.2 X-Ray Detectors.- 3.6 Typical Experimental Arrangements.- 3.6.1 Experiments in the Vacuum Ultraviolet.- a) Absorption Reflection, Ellipsometry.- b) Luminescence, Fluorescence.- c) Photoionisation, Fotofragmentation.- d) Photoemission.- e) Radiometry.- f) Microscopy.- 3.6.2 Experiments in the X-Ray Range.- a) Single Crystal Diffraction.- b) Small Angle Diffraction.- c) Small Angle Scattering.- d) Mossbauer Scattering.- e) Energy Dispersive Diffraction.- f) Interferometry.- g) Absorption (EXAFS).- h) Topography.- i) Standing wave excited Fluorescence.- j) Fluorescence Excitation.- k) Compton Scattering.- 1) Resonant Raman Scattering.- m) Photoelectron Spectroscopy (XPS).- 3.7 Acknowledgements.- References.- 4. Theoretical Aspects of Inner-Level Spectroscopy.- 4. 1. Basic Concepts and Relations in Radiative Processes.- 4.1.1 Polarizability and Dielectric Function.- a) Self-consistent field Method.- b) Direct Method for Longitudinal Part.- 4.1.2 Absorption Coefficient and Oscillator Strength.- 4.1.3 Dispersion Relations and Sum Rules.- 4.2 Distribution of Oscillator Strength.- 4.2.1 Absorption Spectra in Atoms.- 4.2.2 A Unified Picture for Spectra in Atoms, Molecules and Solids.- a) Cancellation of Oscillator Strength, Giant and Subgiant Bands.- b) Pseudo Potential and Energy Band Effect.- c) Effect of Coulomb Attraction.- 4.2.3 Extended X-Ray Absorption Fine Structure (EXAFS).- 4.3 Electron-Hole Interactions.- 4.3.1 General Treatment of Excitons.- 4.3.2 Wannier and Frenkel Excitons.- a) Wannier Exciton.- b) Frenkel Exciton.- 4.3.3 Optical Absorption Spectra.- a) First Class Transition.- b) Second Class Transition.- 4.3.4 Effects of Spin and Orbital Degeneracies.- 4.4 Configuration Interactions.- 4.4.1 Aulger Process.- 4.4.2 Fano Effect.- 4.5 Simultaneous Excitations and Relaxations.- 4.5.1 Localized Excitation and Relaxation in Deformable Lattice.- 4.5.2 Host Excitation in Deformable Medium.- a) Slow Modulation Limit.- b) Rapid Modulation Limit.- 4.5.3 Sideband Structures.- 4.5.4 Relaxation in Exciton-Phonon Systems.- 4.6 Many Body Effects in Metals.- 4.6.1 Friedel Sum Rule and Anderson Orthogonality Theorem.- 4.6.2 Infrared Divergence.- 4.6.3 Fermi Edge Singularity.- 4.7 Final State Interactions Associated with Incomplete Shells.- 4.7.1 Multipiet Splitting.- 4.7.2 Local Versus Band Pictures.- 4.7.3 Correlation Effects in Narrow d-Band.- 4.8 Inelastic X-Ray Scattering.- 4.8.1 Compton and Raman Scattering.- 4.8.2 Resonant Raman Scattering.- 4.9. Topics of Recent and Future Interest.- References.- 5. Atomic Spectroscopy.- 5.1. Atomic Photoabsorption Spectroscopy in the Extreme Ultraviolet.- 5.2 The Basic Experiments in Photoabsorption Spectroscopy.- 5.2.1 Photoabsorption Spectroscopy.- 5.2.2 Photoelectron Spectroscopy.- 5.2.3 Mass Spectrometry.- 5.2.4 Fluorescence.- 5.3 Limitations of Photon Absorption Experiments.- 5.4 The General Theoretical Framework.- 5.5 Experimental Results.- 5.5.1 Photoabsorption Spectroscopy.- a) Discrete Resonances.- b) Gross Features.- 5.5.2 Photoelectron Spectroscopy.- a) Partial Photoionisation Cross Sections.- b) Angular Distributions of Photoelectrons.- 5.5.3 Mass Spectrometry.- 5.6 Future Work.- References.- 6. Molecular Spectroscopy.- 6.1 Concepts.- 6.2 Absorption Spectroscopy.- 6.2.1 Valence Spectra of Simple Di- and Tri-Atomic Molecules.- 6.2.2 Valence and Rydberg Excitations in N2.- 6.2.3 Rydberg Series in the Valence Absorption Spectrum of H2O and D2O.- 6.2.4 Core-Spectra of Simple Di-Atomic and Tri-Atomic Molecules.- a) N2.- b) NO.- 6.2.5 d-Spectra of Se2, Te2 and I2.- a) Se2.- b) Te2.- c) I2.- 6.2.6 Alkali Halides.- a) Li ls-absorption in LiF.- b) Cs-halides.- 6.2.7 Xenon Fluorides.- 6.2.8 Inner-well Resonances.- 6.2.9 EXAFS.- 6.2.10 Valence Shell Spectra of Organic Compounds.- a) Saturated Hydrocarbons: Alkanes, Neopentane.- b) Molecules with bonding o- and -?-orbitals.- 6.2.11 Core Spectra of Organic Compounds.- 6.3 Photoelectron Spectroscopy.- 6.3.1 Intensities of Photoelectron Spectra and Partial Photoionization Cross Sections.- 6.3.2 Photoionization Resonance Spectroscopy and Coincidence Measurements.- 6.4 Fluorescence.- 6.4.1 Fluorescence- and Excitation-Spectra.- 6.4.2 Time resolved Fluorescence Spectroscopy.- 6.5 Mass-Spectrometry.- 6.6. Acknowledgments.- 6.7. Appendix.- References.- 7. Solid-State Spectroscopy.- 7.1 Quantitative Description of Optical Properties.- 7.1.1 Macroscopic Optical Properties.- 7.1.2 Microscopic Description.- 7.1.3 Modulation Spectroscopy.- 7.1.4 Summary.- 7.2 Metals and Alloys.- 7.2.1 Vacuum Ultraviolet.- a) Simple Metals.- b) Noble Metals.- c) Transition Metals.- d) Rare Earths.- 7.2.2 Soft X-Ray.- a) Simple Metals.- b) Transition Metals.- c) Rare Earths.- 7.2.3 Summary.- 7.3 Semi conductors.- 7.3.1 Vacuum Ultraviolet.- a) II-VI Compounds.- b) Pb-Chalcogenides.- c) Other Semiconductors.- 7.3.2 Soft X-ray.- 7.3.3 Summary.- 7.4 Insulators.- 7.4.1 Rare Gas Solids.- 7.4.2 Alkali Hal ides.- 7.4.3 Other Metal Hal ides.- 7.4.4 Other Inorganic Insulators.- 7.4.5 Organic Insulators.- 7.4.6 Summary.- References.- Additional References with Titles.

Structural analysis of unpromoted Fe-based Fischer-Tropsch catalysts using X-ray absorption spectroscopy

Abstract: The structure of unpromoted precipitated Fe catalysts was determined by Mossbauer emission and X-ray absorption spectroscopies after use in the Fischer–Tropsch synthesis (FTS) reaction in well-mixed autoclave reactors for various periods of time. X-ray absorption near-edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS) analysis, and Mossbauer spectroscopy showed consistent trends in the structural evolution of these catalysts during reaction. The nearly complete formation of Fe carbides during initial activation in CO was followed by their gradual re-oxidation to form Fe3O4 with increasing time-on-stream. Fe3O4 became the only detectable Fe compound after 450 h. The observed correlation between FTS rates and Fe carbide concentration, and the unexpected re-oxidation of the catalysts as CO conversion decreased, suggest that the deactivation of Fe catalysts in FTS reactions parallels the conversion of Fe carbides to Fe3O4. It appears that the CO activation steps responsible for replenishing carbidic surface species and for removing chemisorbed oxygen are selectively inhibited by deactivation of surface sites, leading to the oxidation of Fe carbide even in the presence of a reducing reactant mixture. © 2001 Elsevier Science B.V. All rights reserved.

Role of S /Se ratio in chemical bonding of As-S-Se glasses investigated by Raman, x-ray photoelectron, and extended x-ray absorption fine structure spectroscopies

Abstract: Chalcogenide glasses have attracted considerable attention and found various applications due to their infrared transparency and other optical properties. The As–S–Se chalcogenide glass, with its large glass-formation domain and favorable nonlinear property, is a promising candidate system for tailoring important optical properties through modification of glass composition. In this context, a systematic study on ternary As–S–Se glass, chalcogen-rich versus well-studied stochiometric compositions, has been carried out using three different techniques: Raman spectroscopy, x-ray photoelectron spectroscopy, and extended x-ray absorption fine structure spectroscopy. These complementary techniques lead to a consistent understanding of the role of S∕Se ratio in chalcogen-rich As–S–Se glasses, as compared to stochiometric composition, and to provide insight into the structural units (such as the mixed pyramidal units) and evidence for the existence of homopolar bonds (such as Se–Se, S–S, and Se–S), which are the ...

The metal–support interaction in Pt/Y zeolite: evidence for a shift in energy of metal d-valence orbitals by Pt–H shape resonance and atomic XAFS spectroscopy

Abstract: The turnover frequency (TOF) for conversion of neo-pentane was determined for Pt in Y zeolite with different numbers of protons and La C3 ions, different Si/Al ratios and with non-framework Al being present. Comparing Pt/NaY to Pt/H-NaY and Pt/K-USY with Pt/H-USY, respectively, shows an increase in the ln (TOF) which is proportional to the number of protons. Compared to NaY, the TOF of Pt in non-acidic NaLaY zeolite is about 25 times higher, which indicates also a strong influence on the charge of the cations on the TOF of Pt. The 20 times increase in the Pt TOF for K-USY compared to NaY is attributed to the effect of a higher Si/Al ratio and non-framework Al in the K-USY. EXAFS data collected on Pt/NaY and Pt/H-USY showed platinum particles consisting of 14‐20 atoms on an average. These results were confirmed by HRTEM, which also showed that the Pt particles were dispersed inside the zeolite. The EXAFS data indicate that the metal particles are in contact with the oxygen ions of the support. The peak in the Fourier transform of the atomic XAFS (AXAFS) spectrum of the Pt/H-USY is larger in intensity than the corresponding peak of the Pt/Na-Y data. A detailed analysis of the L2 and the L3 X-ray absorption near edge structure revealed a shape resonance due to the Pt‐H anti-bonding state (AS) induced by chemisorption of hydrogen on the surface of the platinum metal particles. The difference in energy (Eres) between the AS and the Fermi-level (EF) is 4.7 eV larger for Pt/H-USY than for Pt/NaY. Both the AXAFS spectra and the shape resonances of the Pt-NaY and the Pt/H-USY catalysts provide direct experimental evidence of how the support properties determine the electronic structure of the platinum metal particles. Previous AXAFS and shape resonance work lead to a model in which the position in energy of the Pt valence orbitals is directly influenced by changes in the potential (i.e. electron charge) of the oxygen ions of the support and how the proton density affects this oxygen charge. This work shows that the potential of the oxygen ions is also a function of the Si/Al ratio of the support and the polarisation power of the charge compensating cations (H C ,N a C ,L a 3C and extra-framework Al); the metal particles experience an interaction which is determined by several properties of the support. The data further reveal how the change in the Pt electronic structure directly influences the catalytic properties of the catalyst. While the TOF is dependent on the metal‐support interaction, the hydrogenolysis selectivity is determined by the Pt particle size, and increases linearly with increasing dispersion, or decreasing particle size. ©2000 Elsevier Science B.V. All rights reserved.