Home About us Contact
|
Home About us Contact | ||
|
|
||
X-ray Absorption Spectroscopy (x-ray + absorption_spectroscopy)
Selected AbstractsChemInform Abstract: Pd,C,Fe Nanoparticles Investigated by X-Ray Absorption Spectroscopy as Electrocatalysts for Oxygen Reduction.CHEMINFORM, Issue 49 2009Yun-Chieh Yeh Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Preparation of Nanocrystalline BaTiO3 Characterized by in situ X-Ray Absorption Spectroscopy.CHEMINFORM, Issue 39 2001Holger Rumpf Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] X-Ray Absorption Spectroscopy of Cuprous-Thiolate Clusters in Saccharomyces cerevisiae MetallothioneinCHEMISTRY & BIODIVERSITY, Issue 10 2008Limei Zhang Abstract Copper (Cu) metallothioneins are cuprous-thiolate proteins that contain multimetallic clusters, and are thought to have dual functions of Cu storage and Cu detoxification. We have used a combination of X-ray absorption spectroscopy (XAS) and density-functional theory (DFT) to investigate the nature of Cu binding to Saccharomyces cerevisiae metallothionein. We found that the XAS of metallothionein prepared, containing a full complement of Cu, was quantitatively consistent with the crystal structure, and that reconstitution of the apo-metallothionein with stoichiometric Cu results in the formation of a tetracopper cluster, indicating cooperative binding of the Cu ions by the metallothionein. [source] Description of the Ground-State Covalencies of the Bis(dithiolato) Transition-Metal Complexes from X-ray Absorption Spectroscopy and Time-Dependent Density-Functional CalculationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2007Kallol Ray Dr. Abstract The electronic structures of [M(LBu)2], (LBu=3,5-di- tert -butyl-1,2-benzenedithiol; M=Ni, Pd, Pt, Cu, Co, Au) complexes and their electrochemically generated oxidized and reduced forms have been investigated by using sulfur K-edge as well as metal K- and L-edge X-ray absorption spectroscopy. The electronic structure content of the sulfur K-edge spectra was determined through detailed comparison of experimental and theoretically calculated spectra. The calculations were based on a new simplified scheme based on quasi-relativistic time-dependent density functional theory (TD-DFT) and proved to be successful in the interpretation of the experimental data. It is shown that dithiolene ligands act as noninnocent ligands that are readily oxidized to the dithiosemiquinonate(,) forms. The extent of electron transfer strongly depends on the effective nuclear charge of the central metal, which in turn is influenced by its formal oxidation state, its position in the periodic table, and scalar relativistic effects for the heavier metals. Thus, the complexes [M(LBu)2], (M=Ni, Pd, Pt) and [Au(LBu)2] are best described as delocalized class,III mixed-valence ligand radicals bound to low-spin d8 central metal ions while [M(LBu)2], (M=Cu, Au) and [M(LBu)2]2, (M=Ni, Pd, Pt) contain completely reduced dithiolato(2,) ligands. The case of [Co(LBu)2], remains ambiguous. On the methodological side, the calculation led to the new result that the transition dipole moment integral is noticeably different for S1s,valence-, versus S1s,valence-, transitions, which is explained on the basis of the differences in radial distortion that accompany chemical bond formation. This is of importance in determining experimental covalencies for complexes with highly covalent metal,sulfur bonds from ligand K-edge absorption spectroscopy. [source] On-line optical and X-ray spectroscopies with crystallography: an integrated approach for determining metalloprotein structures in functionally well defined statesJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2008Mark J. Ellis X-ray-induced redox changes can lead to incorrect assignments of the functional states of metals in metalloprotein crystals. The need for on-line monitoring of the status of metal ions (and other chromophores) during protein crystallography experiments is of growing importance with the use of intense synchrotron X-ray beams. Significant efforts are therefore being made worldwide to combine different spectroscopies in parallel with X-ray crystallographic data collection. Here the implementation and utilization of optical and X-ray absorption spectroscopies on the modern macromolecular crystallography (MX) beamline 10, at the SRS, Daresbury Laboratory, is described. This beamline is equipped with a dedicated monolithic energy-dispersive X-ray fluorescence detector, allowing X-ray absorption spectroscopy (XAS) measurements to be made in situ on the same crystal used to record the diffraction data. In addition, an optical microspectrophotometer has been incorporated on the beamline, thus facilitating combined MX, XAS and optical spectroscopic measurements. By uniting these techniques it is also possible to monitor the status of optically active and optically silent metal centres present in a crystal at the same time. This unique capability has been applied to observe the results of crystallographic data collection on crystals of nitrite reductase from Alcaligenes xylosoxidans, which contains both type-1 and type-2 Cu centres. It is found that the type-1 Cu centre photoreduces quickly, resulting in the loss of the 595,nm peak in the optical spectrum, while the type-2 Cu centre remains in the oxidized state over a much longer time period, for which independent confirmation is provided by XAS data as this centre has an optical spectrum which is barely detectable using microspectrophotometry. This example clearly demonstrates the importance of using two on-line methods, spectroscopy and XAS, for identifying well defined redox states of metalloproteins during crystallographic data collection. [source] Absorption of copper(II) by creosote bush (Larrea tridentata): Use of atomic and x-ray absorption spectroscopyENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2001Jorge Luis Gardea-Torresdey Abstract Larrea tridentata (creosote bush), a common North American native desert shrub, exhibits the ability to take up copper(II) ions rapidly from solution. Following hydroponic studies, U.S. Environmental Protection Agency method 200.3 was used to digest the plant samples, and flame atomic absorption spectroscopy (FAAS) was used to determine the amount of copper taken up in different parts of the plant. The amount of copper(II) found within the roots, stems, and leaves was 13.8, 1.1, and 0.6 mg/g, respectively, after the creosote bush was exposed to a 63.5-ppm copper(II) solution for 48 h. When the plant was exposed to a 635-ppm copper(II) solution, the roots, stems, and leaves contained 35.0, 10.5, and 3.8 mg/g, respectively. In addition to FAAS analysis, x-ray microfluorescence (XRMF) analysis of the plant samples provided further confirmation of copper absorption by the various plant parts. X-ray absorption spectroscopy (XAS) elucidated the oxidation state of the copper absorbed by the plants. The copper(II) absorbed from solution remained as copper(II) bound to oxygen-containing ligands within the plant samples. The results of this study indicate that creosote bush may provide a useful and novel method of removing copper(II) from contaminated soils in an environmentally friendly manner. [source] The Fate of Lead in MSWI-Fly Ash During Heat Treatment: An X-Ray Absorption Spectroscopy Study,ADVANCED ENGINEERING MATERIALS, Issue 6 2009Rudolf Paul Wilhelm Jozef Struis The study focuses on the potential of removing toxifying Pb from a certified, multi-element fly ash (BCR176) by thermal treatment between 300 and 950,°C under different carrier gas compositions (Ar or Ar,+,O2). The treatment was studied by in situ monitoring the evaporation rate of Pb, C, S, Na, and K during heating and by synchrotron X-ray absorption spectroscopy of selected samples collected during vaporization at the Pb L3 -edge. [source] Functional characterization of an orphan cupin protein from Burkholderia xenovorans reveals a mononuclear nonheme Fe2+ -dependent oxygenase that cleaves ,-diketonesFEBS JOURNAL, Issue 20 2009Stefan Leitgeb Cupins constitute a large and widespread superfamily of ,-barrel proteins in which a mononuclear metal site is both a conserved feature of the structure and a source of functional diversity. Metal-binding residues are contributed from two core motifs that provide the signature for the superfamily. On the basis of conservation of this two-motif structure, we have identified an ORF in the genome of Burkholderia xenovorans that encodes a novel cupin protein (Bxe_A2876) of unknown function. Recombinant Bxe_A2876, as isolated from Escherichia coli cell extract, was a homotetramer in solution, and showed mixed fractional occupancy of its 16.1 kDa subunit with metal ligands (0.06 copper; 0.11 iron; 0.17 zinc). Our quest for possible catalytic functions of Bxe_A2876 focused on Cu2+ and Fe2+ oxygenase activities known from related cupin enzymes. Fe2+ elicited enzymatic catalysis of O2 -dependent conversion of various ,-diketone substrates via a nucleophilic mechanism of carbon,carbon bond cleavage. Data from X-ray absorption spectroscopy (XAS) support a five-coordinate or six-coordinate Fe2+ center where the metal is bound by three imidazole nitrogen atoms at 1.98 Å. Results of structure modeling studies suggest that His60, His62 and His102 are the coordinating residues. In the ,best-fit' model, one or two oxygens from water and a carboxylate oxygen (presumably from Glu96) are further ligands of Fe2+ at estimated distances of 2.04 Å and 2.08 Å, respectively. The three-histidine Fe2+ site of Bxe_A2876 is compared to the mononuclear nonheme Fe2+ centers of the structurally related cysteine dioxygenase and acireductone dioxygenase, which also use a facial triad of histidines for binding of their metal cofactor but promote entirely different substrate transformations. [source] Neptunium uptake by serum transferrinFEBS JOURNAL, Issue 7 2005Isabelle Llorens Although of major impact in terms of biological and environmental hazards, interactions of actinide cations with biological molecules are only partially understood. Human serum transferrin (Tf) is one of the major iron carriers in charge of iron regulation in the cell cycle and consequently contamination by actinide cations is a critical issue of nuclear toxicology. Combined X-ray absorption spectroscopy (XAS) and near infrared absorption spectrometry were used to characterize a new complex between Tf and Np (IV) with the synergistic nitrilotriacetic acid (NTA) anion. Description of the neptunium polyhedron within the iron coordination site is given. [source] Structural Characterization of the Transient Amorphous Calcium Carbonate Precursor Phase in Sea Urchin Embryos,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2006Y. Politi Abstract Sea urchin embryos form their calcitic spicular skeletons via a transient precursor phase composed of amorphous calcium carbonate (ACC). Transition of ACC to calcite in whole larvae and isolated spicules during development has been monitored using X-ray absorption spectroscopy (XAS). Remarkably, the changing nature of the mineral phase can clearly be monitored in the whole embryo samples. More detailed analyses of isolated spicules at different stages of development using both XAS and infrared spectroscopy demonstrate that the short-range order of the transient ACC phase resembles calcite, even though infrared spectra show that the spicules are mostly composed of an amorphous mineral phase. The coordination sphere is at first distorted but soon adopts the octahedral symmetry typical of calcite. Long-range lattice rearrangement follows to form the calcite single crystal of the mature spicule. These studies demonstrate the feasibility of real-time monitoring of mineralized-tissue development using XAS, including the structural characterization of transient amorphous phases at the atomic level. [source] Electronic Manifestation of Cation-Vacancy-Induced Magnetic Moments in a Transparent Oxide Semiconductor: Anatase Nb:TiO2ADVANCED MATERIALS, Issue 22 2009Shixiong Zhang Nb-doped anatase TiO2 thin films grown by pulsed-laser deposition show Kondo scattering in elctronic-transport measurements, providing evidence for the formation of magnetic moments. The origin of magnetism is attributed to cation (Ti) vacancies, confirmed by X-ray absorption spectroscopy and first-principle calculations. The Ti vacancies are controlled by oxygen partial pressure during growth. [source] Energy-dispersive X-ray absorption spectroscopy at LNLS: investigation on strongly correlated metal oxidesJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2010Júlio C. Cezar An energy-dispersive X-ray absorption spectroscopy beamline mainly dedicated to X-ray magnetic circular dichroism (XMCD) and material science under extreme conditions has been implemented in a bending-magnet port at the Brazilian Synchrotron Light Laboratory. Here the beamline technical characteristics are described, including the most important aspects of the mechanics, optical elements and detection set-up. The beamline performance is then illustrated through two case studies on strongly correlated transition metal oxides: an XMCD insight into the modifications of the magnetic properties of Cr-doped manganites and the structural deformation in nickel perovskites under high applied pressure. [source] On-line optical and X-ray spectroscopies with crystallography: an integrated approach for determining metalloprotein structures in functionally well defined statesJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2008Mark J. Ellis X-ray-induced redox changes can lead to incorrect assignments of the functional states of metals in metalloprotein crystals. The need for on-line monitoring of the status of metal ions (and other chromophores) during protein crystallography experiments is of growing importance with the use of intense synchrotron X-ray beams. Significant efforts are therefore being made worldwide to combine different spectroscopies in parallel with X-ray crystallographic data collection. Here the implementation and utilization of optical and X-ray absorption spectroscopies on the modern macromolecular crystallography (MX) beamline 10, at the SRS, Daresbury Laboratory, is described. This beamline is equipped with a dedicated monolithic energy-dispersive X-ray fluorescence detector, allowing X-ray absorption spectroscopy (XAS) measurements to be made in situ on the same crystal used to record the diffraction data. In addition, an optical microspectrophotometer has been incorporated on the beamline, thus facilitating combined MX, XAS and optical spectroscopic measurements. By uniting these techniques it is also possible to monitor the status of optically active and optically silent metal centres present in a crystal at the same time. This unique capability has been applied to observe the results of crystallographic data collection on crystals of nitrite reductase from Alcaligenes xylosoxidans, which contains both type-1 and type-2 Cu centres. It is found that the type-1 Cu centre photoreduces quickly, resulting in the loss of the 595,nm peak in the optical spectrum, while the type-2 Cu centre remains in the oxidized state over a much longer time period, for which independent confirmation is provided by XAS data as this centre has an optical spectrum which is barely detectable using microspectrophotometry. This example clearly demonstrates the importance of using two on-line methods, spectroscopy and XAS, for identifying well defined redox states of metalloproteins during crystallographic data collection. [source] XAS and XMCD under high magnetic field and low temperature on the energy-dispersive beamline of the ESRFJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2007O. Mathon The present paper demonstrates the feasibility of X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) under high magnetic fields up to 26,T and low temperatures down to 5,K on the ID24 energy-dispersive XAS beamline of the ESRF. The pulsed magnetic field set-up, entirely developed at the ESRF, is described as well as the beamline set-up, the synchronization and the measurement procedure. It allows field strengths up to 30,T. Finally, as an example, we report a recent XMCD study at the Re L2 and L3 absorption edges of the double perovskite Sr2CrReO6. [source] Energy-dispersive absorption spectroscopy for hard-X-ray micro-XAS applicationsJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2006S. Pascarelli Originally developed for time-resolved X-ray absorption spectroscopy (XAS), energy-dispersive absorption spectroscopy offers new opportunities for applications such as fluorescence detection and microbeams for scanning probe spectroscopy, thanks to recent developments in both instrumentation and optics. In this context, this paper presents a first example of chemical mapping recorded at ID24, the energy-dispersive XAS beamline at the ESRF. Attributes of this geometry for microanalysis are addressed. Finally, present and future plans are discussed and developed in the light of the evolution of the focal spot on this instrument in the past ten years. [source] XAFS experiments at beamline I811, MAX-lab synchrotron source, SwedenJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2006Stefan Carlson A description of a new facility for X-ray absorption spectroscopy at the materials science beamline, I811, at MAX-lab synchrotron source, Lund, Sweden, is given. The beamline is based on a superconducting multipole wiggler source inserted in a straight section of the 1.5,GeV MAX-II ring. X-rays in the energy range 2.4,12,keV are extracted by a standard optical scheme consisting of a vertical collimating first mirror, double-crystal monochromator, and a second vertically focusing mirror. The second monochromator crystal provides sagittal focusing. The total flux impinging on the sample at 9,keV is 5 × 1011,photons,s,1, for a minimum beam spot of 0.5,mm × 0.5,mm. The beamline has facilities for experiments in transmission, fluorescence and total-electron-yield mode and experiments have been performed by international research groups on a wide range of materials, such as dilute systems with metal concentrations below 10,p.p.m. [source] About estimation of fitted parameters' statistical uncertainties in EXAFS.JOURNAL OF SYNCHROTRON RADIATION, Issue 3 2005Critical approach on usual, Monte Carlo methods An important step in X-ray absorption spectroscopy (XAS) analysis is the fitting of a model to the experimental spectra, with a view to obtaining structural parameters. It is important to estimate the errors on these parameters, and three methods are used for this purpose. This article presents the conditions for applying these methods. It is shown that the usual equation is not applicable for fitting in R space or on filtered XAS data; a formula is established to treat these cases, and the equivalence between the usual formula and the brute-force method is evidenced. Lastly, the problem of the nonlinearity of the XAS models and a comparison with Monte Carlo methods are addressed. [source] Specimen charging in X-ray absorption spectroscopy: correction of total electron yield data from stabilized zirconia in the energy range 250,915,eVJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2005Dimitrios Vlachos The effects of specimen charging on X-ray absorption spectroscopy using total electron yield have been investigated using powder samples of zirconia stabilized by a range of oxides. The stabilized zirconia powder was mixed with graphite to minimize the charging but significant modifications of the intensities of features in the X-ray absorption near-edge fine structure (XANES) still occurred. The time dependence of the charging was measured experimentally using a time scan, and an algorithm was developed to use this measured time dependence to correct the effects of the charging. The algorithm assumes that the system approaches the equilibrium state by an exponential decay. The corrected XANES show improved agreement with the electron energy-loss near-edge fine structure obtained from the same samples. [source] Metallogenomics and biological X-ray absorption spectroscopyJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2005Isabella Ascone An overview of the second special issue of the journal on biological applications of X-ray absorption spectroscopy (BioXAS) is presented. The emphasis is on the study of metalloproteins in the context of structural genomics programmes (metallogenomics). [source] Theory of Ca L2,3 -edge XAS using a novel multichannel multiple-scattering methodJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2005Peter Krüger A new method for calculating X-ray absorption spectroscopy (XAS) at the L2,3 edges of Ca and transition metals is presented. It is based on the multichannel multiple-scattering theory by Natoli et al. [Phys. Rev. B, (1990), 42, 1944,1968] combined with the eigen-channel R-matrix formalism. Atomic multiplet-like effects, owing to the Coulomb interaction of photoelectrons and the 2p hole, are taken into account through a configuration interaction ansatz for the final-state wavefunction. The various multiplet states lead to a set of channels for the photoelectron wavefunction, which is calculated in multiple-scattering theory. The method is applied to Ca, an important element for biological applications of XAS. An L:L branching ratio of 3:4 is found, in good agreement with experiment but in contrast to the statistical value 2:1 obtained in all one-electron approaches. By using a linear mixture between statically screened (,90%) and unscreened (,10%) core-hole potential, the line shape, too, agrees well with the experimental one. [source] Introductory overview: X-ray absorption spectroscopy and structural genomicsJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2003Isabella Ascone A special issue of the journal is presented, dedicated to biological applications of X-ray absorption spectroscopy (BioXAS) and examining the role of this technique in post-genomic biology. The issue confirms that BioXAS has come of age and it can be expected to make a significant contribution in the structural genomics effort on metalloproteins, which are estimated to make up about 30% of proteins coded by genomes. [source] X-ray absorption spectroscopy to watch catalysis by metalloenzymes: status and perspectives discussed for the water-splitting manganese complex of photosynthesisJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2003Holger Dau Understanding structure,function relations is one of the main interests in the molecular biosciences. X-ray absorption spectroscopy of biological samples (BioXAS) has gained the status of a useful tool for characterization of the structure of protein-bound metal centers with respect to the electronic structure (oxidation states, orbital occupancies) and atomic structure (arrangement of ligand atoms). Owing to progress in the performance characteristics of synchrotron radiation sources and of experimental stations dedicated to the study of (ultra-dilute) biological samples, it is now possible to carry out new types of BioXAS experiments, which have been impracticable in the past. Of particular interest are approaches to follow biological catalysis at metal sites by characterization of functionally relevant structural changes. In this article, the first steps towards the use of BioXAS to `watch' biological catalysis are reviewed for the water-splitting reactions occurring at the manganese complex of photosynthesis. The following aspects are considered: the role of BioXAS in life sciences; methodological aspects of BioXAS; catalysis at the Mn complex of photosynthesis; combination of EXAFS and crystallographic information; the freeze-quench technique to capture semi-stable states; time-resolved BioXAS using a freeze-quench approach; room-temperature experiments and `real-time' BioXAS; tasks and perspectives. [source] EXAFS and molecular dynamics studies of ionic solutionsJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Paola D'Angelo This paper focuses on recent advances in the X-ray absorption spectroscopy (XAS) analysis of ionic solutions. The asymmetry of radial distribution functions associated with the solvent molecules surrounding the ions has to be taken into account to perform a reliable structural analysis. Molecular dynamics (MD) simulations provide reliable 's which can be used as starting models in the XAS data analysis. The combined MD-XAS investigation reduces meaningfully the indetermination of the structural parameters, especially for coordination numbers and Debye,Waller factors. Double-electron excitation channels can be present in the XAS spectra of ionic solutions and they have to be accounted for in the background extraction. The ability of the XAS technique to probe three-body correlation functions in ionic solutions with the aid of MD has been shown. The analysis of the low- k region of the spectra allows the detection of a weak but significant hydrogen structural signal. The XAS technique is especially well suited to determine the detailed shape of the nearest-neighbor peak in the atom,atom pair correlation functions of disordered systems. The information that they contain about the short-range atom,atom pairwise interactions can be very helpful for specifying and properly modifying model potentials used in MD simulations. [source] High-resolution soft X-ray absorption spectroscopy of solidsJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Y. Saitoh The present research deals with the high-resolution soft x-ray absorption spectra (XAS) of Si, Ce- and Sm- compounds measured at BL25SU of SPring-8. The spectra are compared with theoretical results. The Si 1s spectrum shows good agreement with the calculated empty density of states so far reported. The Ce 3d spectra are very sensitive to the local electronic structure. The Sm 3d XAS of SmS shows clear temperature dependence, which is partly explained by a calculation for Sm2+ ion. [source] Solid-state kinetics from time-resolved in situ XAFS investigations: reduction and oxidation of molybdenum oxidesJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001T. Ressler The reduction of MoO3 with hydrogen was studied by in situ X-ray absorption spectroscopy. The experiments performed focused on elucidating phase composition and evolution with time under isothermal reduction conditions. From temperature programmed experiments short-range structural details about the early stage of the reduction were obtained. [source] XAS-Collect: a computer program for X-ray absorption spectroscopic data acquisitionJOURNAL OF SYNCHROTRON RADIATION, Issue 4 2000Martin J. George A computer program for X-ray absorption spectroscopy (XAS) data acquisition, called XAS-Collect, is described. The software employs the X Windows system to provide a pull-down menu, dialog-box style of graphical user interface. The software provides state-of-the-art features while still being sufficiently simple for novice users. [source] VUV-ellipsometry on GaN: Probing conduction band properties by core level excitationsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2005N. Esser Abstract Spectral ellipsometry is a widely used method for analysing optical properties of materials. In particular electronic interband transitions of many semiconductor materials have been intensively studied employing ellipsometry from the near-infrared to the ultra-violet (UV) spectral range. Electronic excitations involving core-levels, on the other hand, have been a domain of synchrotron based X-ray absorption spectroscopy or electron loss spectroscopy. We apply spectral ellipsometry in the vacuum-UV spectral range to study core level excitations in GaN. The results proof that VUV-ellipsometry is a very versatile tool to obtain information on the p-like component of the density of states (DOS) related to the conduction bands of GaN. Excitations of the 3d core level of Ga are shown to be linked to the partial DOS at the Ga site within the lattice (complementary to the information obtained on nitrogen sites by X-ray absorption at the N1s edge). (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Soft X-ray absorption spectroscopy and magnetic circular dichroism study of electroless-deposited CoNiFe ternary alloy soft magnetic filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006Masahito Tanaka Abstract We studied microscopic magnetic properties of each consistent atom in boron added CoNiFe electroless-deposited soft magnetic films, which is a promising candidate for the soft magnetic underlayer of the perpendicular magnetic recording medium, by X-ray absorption spectra (XAS) and magnetic circular dichroism (MCD) measurement. It was found that various monoxides and Fe sesquioxide coexisted with the metals at the upper part of the films. The results of MCD sum rule showed the expected values of orbital angular moment ,Lz, for the film with macroscopic magnetic domain boundaries were larger than those of without domains at Co and Ni atoms and smaller at Fe atom. The appearance of macroscopic magnetic domain boundaries probably originated from the increase in ,Lz, of Co and/or Ni atoms. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of hydrogen intercalation on the local structure around Re ions in perovskite-type ReO3PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005J. Gaidelene Abstract In-situ X-ray absorption spectroscopy at the Re L1 and L3 edges was used to study a modification of the local atomic and electronic structure around rhenium in perovskite-type ReO3 upon hydrogen intercalation. The analysis of both EXAFS and XANES parts of the X-ray absorption spectra shows an evidence of the charge disproportionation phenomenon in hydrogenated rhenium trioxide. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Picosecond and femtosecond X-ray absorption spectroscopy of molecular systemsACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2010Majed Chergui The need to visualize molecular structure in the course of a chemical reaction, a phase transformation or a biological function has been a dream of scientists for decades. The development of time-resolved X-ray and electron-based methods is making this true. X-ray absorption spectroscopy is ideal for the study of structural dynamics in liquids, because it can be implemented in amorphous media. Furthermore, it is chemically selective. Using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) in laser pump/X-ray probe experiments allows the retrieval of the local geometric structure of the system under study, but also the underlying photoinduced electronic structure changes that drive the structural dynamics. Recent developments in picosecond and femtosecond X-ray absorption spectroscopy applied to molecular systems in solution are reviewed: examples on ultrafast photoinduced processes such as intramolecular electron transfer, low-to-high spin change, and bond formation are presented. [source] | |||||||||||||||||||