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Showing papers on "XANES published in 1992"


Journal ArticleDOI
06 Nov 1992-Science
TL;DR: The scanning transmission x-ray microscope at the National Synchrotron Light Source has been used to record XANES spectra from 0.01-square-micrometer regions of organic specimens to identify and map separate phases in various polymer blends and to map the DNA distribution in chromosomes.
Abstract: The scanning transmission x-ray microscope at the National Synchrotron Light Source has been used to record x-ray absorption near-edge structure (XANES) spectra from 0.01-square-micrometer regions of organic specimens. The spectral features observed reflect the molecular structure of the dominant absorbing atoms and provide the contrast mechanism for high-resolution imaging with chemical sensitivity. This technique was used with x-ray energies near the carbon K absorption edge to identify and map separate phases in various polymer blends and to map the DNA distribution in chromosomes with a spatial resolution of 55 nanometers.

358 citations


Journal ArticleDOI
TL;DR: By probing the local atomic environment of strontium coprecipitated with natural and synthetic calcites, X-ray absorption spectroscopy (XAS) reveals that the Str2+-O2− distance derived from EXAFS, 258 ± 003A, is consistent with the sum of the radii of these two ions in six and threefold coordination, respectively, of 257 A as discussed by the authors.

101 citations


Journal ArticleDOI
TL;DR: XANES of vanadium and niobium oxide on silica or alumina have been analyzed quantitatively by a deconvolution technique as discussed by the authors, based on the results for reference compounds.
Abstract: XANES of vanadium and niobium oxide on silica or alumina have been analyzed quantitatively by a deconvolution technique. Based on the results for reference compounds, local structures of supported vanadium and niobium species were identified. The composition was estimated from difference spectra for the samples which consisted of two kinds of species.

97 citations


Journal ArticleDOI
D. Trong On1, Laurent Bonneviot1, A. Bittar1, A. Sayari1, Serge Kaliaguine1 
TL;DR: In this article, three titanium silicalite samples with MEL structure and different Ti loadings have been examined by Near-Edge and Extended X-ray Absorption Fine Structure techniques.

97 citations


Journal ArticleDOI
TL;DR: In this article, the structure of acetylene adsorbed on Pd(111) below ∼ 200 K was probed using near-edge X-ray absorption fine structure (NEXAFS) and ultraviolet and Xray photoelectron spectroscopy.

77 citations


Journal ArticleDOI
TL;DR: In this paper, the behavior of all major sulfur forms during in situ high-temperature oxidation and pyrolysis was derived for two US bituminous coals and a low-rank Australian brown coal from least-squares analysis of sulfur K-edge X-ray absorption nearedge structure spectra taken at constant temperatures up to 600°C.
Abstract: Sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy has been utilized to conduct the first direct characterization and quantification of sulfur functional groups in coal during in situ high-temperature oxidation and pyrolysis. The behavior of all major sulfur forms during such treatments was derived for two US bituminous coals and a low-rank Australian brown coal from least-squares analysis of sulfur K-edge XANES spectra taken at constant temperatures up to 600°C. During pyrolysis, pyrite began to convert to pyrrhotite at temperatures above 400°C

70 citations


Journal ArticleDOI
TL;DR: In this paper, the reduction of bimetallic silica-supported Pt/Ni chloride precursors was followed by means of X-ray absorption spectroscopy and quantitative analysis of the near-edge structures of the Pt L{sub III} and the Ni K edge was used to follow the reduction kinetics of each metal phase.
Abstract: The reduction of bimetallic silica-supported Pt/Ni chloride catalyst precursors was followed by means of X-ray absorption spectroscopy. Quantitative analysis of the near-edge structures (XANES) of the Pt L{sub III} and the Ni K edge was used to follow the reduction kinetics of each metal phase. The reduction to the final material occurred in two steps: In the first, the reduction of Pt atoms and Ni atoms adjacent to Pt took place (forming a bimetallic phase); in the second, the reduction of the remaining Ni atoms occurred (forming a separate Ni phase). In the reduced bimetallic particles, XANES indicates electron transfer from Ni to Pt atoms compared to the monometallic particles. 30 refs., 8 figs., 1 tab.

62 citations


Journal ArticleDOI
TL;DR: In this paper, in situ X-ray absorption spectroscopy measurements at the Pt L3 edge are reported for a high surface area platinum on carbon fuel cell type electrode in 1 M H2SO4 at 20°C.

60 citations


Journal ArticleDOI
TL;DR: The XANES spectrum of a DNA sample with a known ratio of the polyn nucleotides is equivalent to the weighted sum of the spectra of individual polynucleotides, indicating that the difference in base stacking interactions produces negligible spectral effects.

56 citations


Journal ArticleDOI
01 Jun 1992-Fuel
TL;DR: The sulphur L-edge X-ray absorption near-edge structure (XANES) spectra of several model organic and inorganic sulphur compounds have been recorded using monochromatized synchrotron radiation as discussed by the authors.

55 citations


Journal ArticleDOI
TL;DR: In this article, the passive film on sputter deposited thin film Fe-26Cr electrodes has been examined using the technique of in situ X-ray absorption near edge spectroscopy (XANES).
Abstract: The passive film on sputter deposited thin film Fe-26Cr electrodes has been examined using the technique of in situ X-ray absorption near edge spectroscopy (XANES). During the X-ray spectroscopic measurements, the sample was maintained under electrochemical control in the pH 8.4 borate buffer electrolyte. The appearance of the distinctive Cr(VI) XANES pre-edge peak can be correlated with the transpassive wave in the cyclic voltammogram, and its disappearance with the corresponding reduction wave. The formation and reduction of Cr(VI) was reversible, and only small amounts were detected in the film. Cr(VI) in the passive film is not indefinitely stable, and it is completely absent after long periods of air exposure.

Journal ArticleDOI
TL;DR: In this article, the X-ray absorption near-edge structure (XANES) was used to determine the structure of the S-passivated InP(100)−(1×1) surface.
Abstract: X‐ray absorption near‐edge structure (XANES) is used to determine the structure of the S‐passivated InP(100)‐(1×1) surface. From photon electric polarization‐dependent XANES studies, we found that S forms a bridge bond with two In atoms along the [011] direction, with an In‐S‐In bond angle of 100°. The atomic position of S is found to be close to the tetrahedral site of a phosphorous vacancy.

Journal ArticleDOI
01 Sep 1992
TL;DR: In this article, multiple scattering calculations using clusters of two shells around the oxygen and silicon atoms, respectively, are in good agreement with experimental absorption spectra and confirm mean Si-O-Si angles between 130 and 144° for these samples, and a decrease of the mean angle with densification.
Abstract: The decrease of the mean Si-O-Si angle in vitreous silica upon densification from 2.20 to 2.36 gcm-3 has been followed by oxygen and silicon K-edge XANES spectroscopy. Multiple scattering calculations using clusters of two shells around the oxygen and silicon atoms, respectively, are in good agreement with experimental absorption spectra and confirm mean Si-O-Si angles between 130 and 144° for these samples, and a decrease of the mean angle with densification. The experimental spectra also exhibit features due to scattering at outer (>2) shells around the photoabsorbers.

Journal ArticleDOI
TL;DR: The edges in X-ray absorption spectra exhibit fine structures designated as XANES (Xray absorption near edge structure) and EXAFS (extended Xray absorption fine structure).
Abstract: The edges in X-ray absorption spectra exhibit fine structures designated as XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure). The information content of EXAFS with regard to interatomic distances, coordination number, and the determination of degrees of order was presented in the first part of this article [Trends Anal. Chem., 11 (1992) 218]. The second part deals with the fine structures near to the edge, the XANES region, which contains information about the electronic and the geometric structure of the absorbing atom.

Journal ArticleDOI
TL;DR: In this article, an extended X-ray-absorption near-edge structure (XANES) and extended-x-ray absorption fine-structure (EXAFS) measurements have been performed on the calcium K edge and manganese K edge of a sample doped with manganous at molecular concentrations of 0.1--2.5 %.
Abstract: X-ray-absorption near-edge structure (XANES) and extended-x-ray-absorption fine-structure (EXAFS) measurements have been performed on the calcium K edge and manganese K edge of ${\mathrm{CaF}}_{2}$ doped with manganese at molecular concentrations of 0.1--2.5 %. The results are compared to other measurements of the calcium K edge in ${\mathrm{CaF}}_{2}$ and the Mn K edge in various manganese compounds. Major features in the XANES spectra are tentatively identified with transitions to high-symmetry points of the ${\mathrm{CaF}}_{2}$ energy bands in a one-electron picture. Expected deviations from the structure predicted by the one-electron formalism are discussed. The EXAFS analysis shows a reduction in the manganese-fluorine distance of (3.9\ifmmode\pm\else\textpm\fi{}0.4)% as compared to the calcium-fluorine separation in the doped or undoped samples. This compares well with previous results obtained by EPR. A significant increase in disorder of the first shell around the Mn dopant ion is observed as compared to the Ca ion. The significance of this shell contraction and disorder is discussed in terms of possible defect structures in the material.

Journal ArticleDOI
TL;DR: In this paper, the structure of vanadium oxide overlayers of V2O5/SiO2 catalysts prepared by chemical vapour deposition (CVD) and impregnation methods has been determined by using vanadium K-edge EXAFS and XANES.
Abstract: The structure of vanadium oxide overlayers of V2O5/SiO2 catalysts prepared by chemical vapour deposition (CVD) and impregnation methods has been determined by using vanadium K-edge EXAFS and XANES. The Fourier transform of EXAFS for the vanadium oxide overlayers obtained by CVD of VO(OC2H5)3 showed very weak peaks due to V—O—V bonds, even at the high loading level of V2O5(17 wt.%), while crystalline V2O5 gave strong peaks due to V—O and V—O—V bonds. On the basis of the EXAFS and XANES results, it has been concluded that the vanadium oxides obtained by the CVD method were present as thin overlayers on SiO2, and were stable to calcination at 773 K. On the other hand, with an impregnation method, XANES of V2O5/SiO2 at loading levels less than 5 wt.% gave peaks different from those of crystalline V2O5. It was presumed that an isolated V species was formed as reported in the literature. At loading levels >5 wt.%, XANES and EXAFS for V2O5/SiO2 catalysts prepared by the impregnation method were very similar to those of crystalline V2O5, indicating that crystallites of V2O5were formed on SiO2 in this case. This occurs because aggregates of vanadium compounds, e.g. oxalate, were formed as precursors of V2O5 during the drying process.

Journal ArticleDOI
TL;DR: In this article, X-ray absorption fine structure (XAFS) analyses have been used to obtain a better understanding of the support effects on the structure of the calcined catalysts.

Journal ArticleDOI
TL;DR: In this paper, the authors applied X-ray absorption spectroscopy to the study of RE2Fe14BHx (RE La, Ce) and Ce2Fe17Hx systems at variable hydrogen concentration.

Journal ArticleDOI
TL;DR: In this article, the structure of the (0110) α-quartz surface after different treatments (900°C vacuum or air heating and ion bombardment) was investigated by low energy electron diffraction (LEED), the mean-range order by X-ray absorption spectroscopy at the oxygen K edge (XANES) and the electronic structure of surface band gap by low-energy electron loss spectroscope (ELS).

Journal ArticleDOI
TL;DR: In this paper, a correlation between the bond lengths and the term values of the shape resonances was extracted from the experimental data, and the results in multiple scattering (MS)-Xα calculations of (PO 3 ) 3 − and (PO 4 ) 3− clusters were assumed to comprise all the interactions which are of relevance for the complete molecules.

Journal ArticleDOI
TL;DR: In this paper, the XANES spectra of oxidic silver(I) compounds exhibit a prominent peak at the rising edge, indicating a transition from initial 2p states to 4d final states.

Journal ArticleDOI
T. Liu, K. Asakura, U. Lee, Yoshio Matsui, Y. Iwasawa 
TL;DR: In this article, the Anderson-type plane [PtMo 6 O 24 ] 8− heteropolyanion was used to support bimetallic ensembles on silica and alumina.

Journal ArticleDOI
TL;DR: In this paper, the electron yield spectrum of 1,3,5-trans-hexatriene was obtained by measuring the total yield of electrons as a function of photon energy.

Journal ArticleDOI
TL;DR: In this paper, the results of the chromium K-edge XANES and EXAFS (Extended X-ray Absorption Fine Structure) data were obtained for a thick, porous aluminum oxide film sealed in dichromate solution.

Journal ArticleDOI
14 Feb 1992-EPL
TL;DR: In this article, the authors follow the cluster formation when depositing less than 2 monolayers Cu onto a monocrystalline αAl2O3 (0001) stoichiometric surface, by combining XPS and X-ray absorption spectroscopy at the Cu K edge (EXAFS, XANES).
Abstract: We follow the cluster formation when depositing less than 2 monolayers Cu onto a monocrystalline αAl2O3 (0001) stoichiometric surface, by combining XPS and X-ray absorption spectroscopy at the Cu K edge (EXAFS, XANES). An estimate of the evolution of cluster size with copper deposition is given from XANES and EXAFS data. The variation of the Cu Auger parameter, measured from the XPS spectra, shows a continuous increase, attributed to the continuous increase of cluster size with copper deposition.

Journal ArticleDOI
TL;DR: In this paper, radio-frequency-sputtered Co/Fe multilayers with layer thickness varying in the 8-100 A range were studied by extended x-ray absorption fine structure (EXAFS), xray absorption near edge spectroscopy (XANES), and nuclear magnetic resonance (NMR) techniques.
Abstract: Radio‐frequency‐sputtered Co/Fe multilayers with layer thicknesses varying in the 8–100 A range were studied by extended x‐ray absorption fine structure (EXAFS), x‐ray absorption near edge spectroscopy (XANES), and nuclear magnetic resonance (NMR) techniques. While the Fe environment is body‐centered‐cubic (bcc) in all the samples, the Co environment depends drastically on the Co layer thickness. Under ≂20 A, investigation at the Co K edge by XANES provides a bcc fingerprint in both polarization directions. The XANES profile becomes typical of a full hcp stacking only for Co layer thicknesses larger than 98 A. This behavior is confirmed by EXAFS spectra at the Co K edge and NMR analysis. For Co layer thickness between 6 and 18 A, eight first neighbors at 2.48 A and six second neighbors at 2.83 A are detected which match the bcc phase. Resonance peak at a very low frequency is also observed (198 MHz). The second shell radius appears at 2.78 A only for larger Co layer thicknesses. This effect goes along wit...

Journal ArticleDOI
TL;DR: In this article, the authors examined the local structure of the As x Se 1− x (0.20≤ x ⁤57) system by Extended X-ray Absorption Fine Structure (EXAFS) measurements.

Journal ArticleDOI
TL;DR: In this paper, the X-rays Absorption Near Edge Structure of Ce adsorbed on d-Mn02(s) was determined using synchrotron radiation.
Abstract: Sorption equilibria and kinetics involving Eu and Ce at the surface of hydroxylapatite and manganese oxide in aqueous solutions were examined by non-invasive spectroscopic techniques. The X-rays Absorption Near Edge Structure of Ce adsorbed on d-Mn02(s) was determined using synchrotron radiation. A surface-mediated redox transformation of Ce(III) to Ce(IV) was observed. The rate of Eu adsorption and incorporation into the hydroxylapatite structure was studied by direct observation of the reacting suspension using Time Resolved Laser Induced Fluorescence. The process was found to be remarkably influenced by the aqueous speciation of Eu initially added to the mineral/water suspension.

Journal ArticleDOI
TL;DR: In this article, x-ray absorption near edge structure (XANES) measurements were made in air immediately following polarization in solution, and the effects of alloy composition and thickness as well as applied potential were studied.
Abstract: Oxides grown electrochemically in a borate buffer solution on the surface of sputterdeposited AlCr alloy films were studied by x-ray absorption near edge structure (XANES). The measurements were made in air immediately following polarization in solution. The oxides were also examined with x-ray photoelectron spectroscopy (XPS). The effects of alloy composition and thickness as well as applied potential were studied. Cr( VI) was found in the oxides if the applied potential was sufficiently high. The Cr(VI) was enriched at the interface with the electrolyte and the proportion of Cr(VI) in the oxide was higher for alloy films containing more Cr. The Cr(VI) in the oxides could be reversibly reduced to Cr(III) and reoxidized to Cr(VI) by subsequent potentiostatic treatments in solution.

Journal ArticleDOI
TL;DR: The conclusions from the calculations indicate that the pre-edge feature in the experimental Cu- and Fe-edge data for chalcopyrite can be due to interference effects from the atomic structure surrounding the absorber, but cannot exclude the possibility that it is due to atomic bound-state transitions of the absorbers.
Abstract: X-ray-absorption near-edge structure (XANES) data were collected for Zn in sphalerite (ZnS), and for Cu and Fe in chalcopyrite (${\mathrm{CuFeS}}_{2}$), where all three cations are in nearly identical coordination environments. The data have similar features, except near the edge, where the edge maximum decreases in amplitude, while a pre-edge feature appears and increases in amplitude from Zn to Cu to Fe. The pre-edge feature was previously assigned to a 1s-to-3d atomic transition for Cu and Fe in the chalcopyrite structure. XANES calculations were performed for all three edges. The multiple- and single-scattering contributions to the calculated edge spectra were scaled down to better fit the experimental data. The conclusions from the calculations indicate that the pre-edge feature in the experimental Cu- and Fe-edge data for chalcopyrite can be due to interference effects from the atomic structure surrounding the absorber, but cannot exclude the possibility that the pre-edge feature is due to atomic bound-state transitions of the absorber.