bluuebunny/crossref_metadata_2025 huggingface dataset:
Real-Time Probe of Reaction Centers in Solid Combustions by QEXAFS on the Sub-Second Time Scale
Authors: Frahm R. , Wong Joe , Holt J. B. , Larson E. M. , Rupp B. , Waide P. A.
Published: March 2014

A QEXAFS (quick-scanning EXAFS) technique has been devised to follow the local atomic coordination changes about selected reactants in a class of highly exothermic solid combustion reactions. Real-time EXAFS measurements during the combustion were made in the time frame of a few seconds. By tuning the monochromator to a specific energy, at which maximum changes occur in an EXAFS feature of an element transforming from the reactant to the product phase, a time resolution of 20 ms was achieved. The Ni + Al → NiAl reaction has been investigated in some detail in light of a possible intermediate phase in the so-called after-burn region. The present QEXAFS findings together with the recent time-resolved diffraction data on the same system lends, for the first time, experimental insights into the structural macrokinetics of this class of combustion systems.
Distortion of XAFS Spectra Recorded with X-ray Excited Optical Luminescence
Authors: Gauther Christophe , Emerich Hermann , Goulon José
Published: March 2014

We have measured the XAFS spectra of a thick powdered sample of EuCl2 at the L edges of Eu using the X-Ray excitation of optical luminescence (XEOL). The spectra exhibit a strong distortion resulting in an apparent derivative like shape. We propose an extension of the phenomenological theory developed recently by Emura et al. to include the case of non transparent samples. Whenever the self-absorption is significant, then the shape of the excitation spectra depends on the direction of emission.
Developments in the Design of Efficient X-ray Optical Elements Using Large Arrays of Glass Capillaries
Authors: Hayes T. M. , Kovantsev V. E. , Pant J. , Pantojas V. , Nazaryan N. , Persans P. D.
Published: March 2014

We have characterized an optical element designed to convert divergent x rays into a quasi-parallel beam. For Cu K radiation, it transmits four times the x-ray power of a slit-based collimation system of comparable energy resolution.
Comparison between XAS, AWAXS and DAFS Applied to Nanometer Scale Supported Metallic Clusters: Part I Monometallic Clusters
Authors: Bazin Dominique C. , Sayers Dale A.
Published: March 2014

The structural information found using three techniques related to synchrotron radiation are compared. XAS (X-ray Absorption Spectroscopy), AWAXS (Anomalous Wide Angle X-ray Scattering) and DAFS (Diffraction Anomalous Fine Structure) are applied to nanometer scale metallic clusters.
Recent Improvements in Laboratory XAFS Facility
Authors: Nishihagi Kazuo , Kawabata Atusi , Taniguchi Kazuo
Published: March 2014

It has been said that Laboratory XAFS measurement takes long time due to weak X-Ray source and that it is not suitable for XANES measurement due to its poor resolution. However, recently, some improvements and developments, i. e. highly brilliant X-Ray source, LaB6 cathode, high speed counting circuit, engineering workstation etc. have been realizing competitive performance and measurement circumstances with SR(Synchrotron Radiation).
A Laboratory EXAFS Study with Higher-Order Bragg Reflection by Means of the Fluorescence Monitoring Technique
Authors: Omote Kazuhiko , Tohji Kazuyuki , Waseda Yoshio
Published: March 2014

A Laboratory EXAFS study has been tested by using higher-order Bragg reflections of Ge(440), Ge(333) and Ge(444). A single crystal spectrometer was employed and the incident x-ray intensity was monitored by measuring the fluorescent radiation from a suitable material placed in front of a sample. Good EXAFS spectra were obtained for relatively heavy elements of Se, Y and Zr with this technique. In addition, high intensity photon fluxes have been obtained, which are 6 and 3 times stronger than the case of double-crystal spectrometer at photon energies of 12 and 16 keV, respectively.
In-House Measurements of XAFS by Means of Total Reflection
Authors: Tani Katsuhiko , Katsuragawa Tadao , Chiba Eriko , Okada Kenji
Published: March 2014

We have developed a double channel-cut monochromator composed of two channel-cut Si(111) crystals, and obtained highly parallel and highly monochromatized X-ray beam. Reflectivity of an As2Se3 film on an Al substrate was measured as a function of photon glancing angle around the critical one of total reflection. The complex refractive index was determined so that the simulated Fresnel reflectivity fits the measured values. Since the imaginary part of the refractive index is correlated with the linear absorption coefficient, we can obtain XAFS spectrum by means of reflectivity measurements in house.
Many Body Effects in the X-ray Absorption Edge of Rare-Earth Systems
Authors: Kotani Akio
Published: March 2014

A review is presented of many body effects originating from intraatomic multiplet coupling and interatomic hybridization in the X-ray absorption spectra (XAS) of rare-earth systems. With CeO2 as an example, the Ce N
4,5, M
4,5 and L
3 XAS are theoretically analyzed with the impurity Anderson model, and the importance of the interplay between the multiplet coupling and the hybridization is shown for N
4,5 and M
4,5 XAS. Then we calculate a pre-edge structure of L
3 XAS in Dy compounds, and discuss an elimination of the lifetime broadening in the L
3 XAS, which has recently been attained experimentally by observing the excitation spectrum of L
3-M
5 X-ray emission.
Electronic Structure from Iron L-edge Spectroscopy: An Example of Spin Transition Evidenced by Soft X-ray Absorption Spectroscopy
Authors: Moulin Ch. Carder dit , Flank A. M. , Rudolf P. , Chen C. T.
Published: March 2014

Soft X-ray Absorption Spectroscopy at the transition metal L2,3 edges provides information about the 3d unoccupied states by dipole allowed transitions. We have recorded iron L2,3 edges in order to follow the reversible thermal spin interconversion (S=2 \leftrightarrows S=0) of the Fe(II)(o-phenantroline)2(NCS)2. Huge differences are observed which demonstrate that the L2,3 metal edges are a good fingerprint of the spin state and can be used to evidence an interconversion of the spin state.
X-Ray Magnetic Circular Dichroism in Crystalline and Amorphous Fe–Dy Alloys
Authors: Kobayashi Kenji , Maruyama Hiroshi , Maeda Hironobu , Yamazaki Hitoshi
Published: March 2014

X-ray magnetic circular dichroism has been studied on the crystalline and amorphous 80at%Fe-R(R=Sm,Gd,Tb and Dy) alloys. The dichroic spectrum at the Fe K-edge suggests that Fe 4p-bands hybridize with unoccupied bands of rare-earth. The intensity ratio between the XMCD spectra at the R L
2- and L
3-edges deviates from the ratio 1:-1 theoretically expected, which indicates a non-vanishing orbital angular momentum.
X-ray Magnetic Circular Dichroism at Ho L2,3-edges in Ho-Iron-Garnet
Authors: Shimomi Kimito , Maruyama Hiroshi , Kobayashi Kenji , Koizumi Akihisa , Yamazaki Hitoshi , Iwazumi Toshiaki
Published: March 2014

Angle-dependent X-ray magnetic circular dichroism has been measured to make clear quadrupolar contribution to the dichroic spectrum at the Ho L
2,3-edges in holmium-iron-garnet. A distinction between dipolar and quadrupolar contributions is made on the basis of the recently developed theory. The experimental result is not consistent with the theoretical predictions.
Observation of X-ray Magnetic Kerr Rotation at Gd L Absorption Edges
Authors: Mori Koichi , Namikawa Kazumichi , Koyama Yasuki , Ando Masami
Published: March 2014

The first observation of the rotation of the major axis on the scattered X-ray at magnetic resonance has been performed. This rotatory power named “X-ray Magnetic Kerr Effect” is applicable to the investigation of spin polarization of unoccupied states. The rotation has been measured with 1eV increment between 6eV below the Gd L3 absorption edge and 6eV above the Gd L3 absorption edge. The maximum rotation is about minus 2 degrees observed at about 4eV below the edge. The peak width is about 2eV. This spectrum correspond to the 4f-state. The magnitude of the rotation between 3eV below the edge and 5eV above the edge is about 1 degree. The sign of the rotation change from plus to minus at the vicinity of the edge. This spectrum correspond to the 5d-band structure. These features agree fairly well with the theoretical prediction.
Multiple Scattering Effects in Polarisation-Dependent Surface EXAFS
Authors: Binsted N. , Norman D.
Published: March 2014

We investigate the effect of multiple scattering (MS) on the X-ray absorption spectrum using full curved wave theory with exact polarisation dependence and including orders of MS up to five. As well as the EXAFS, much of the near-edge region can be fitted using an algorithm which includes a sufficiently small number of MS paths to make routine calculation feasible. Results are presented for the model c(2×2) overlayer of atomic O in the fourfold hollow on an unreconstructed Cu(100) surface and in the long bridge site on the (110) surface. MS is important for some polarisation directions, and failure to include at least the dominant double scattering terms may result in errors in the parameters for some non-nearest neighbour distances. We derive general rules for when MS is likely to influence surface EXAFS. The dominant MS paths involve the shortest bonds in the material. Most of the significant paths involve either one small (<45°) or large (>150°) scattering angle, with the most favourable geometry for MS being when forward scattering occurs at a light atom and backscattering at a heavy atom. Polarisation dependence tends to select those contributions where the ε-vector is roughly parallel to one of these bonds. Multiple scattering effects are likely to be strongest when adsorbate atoms occupy sites close to coplanar with the surface. The presence of MS peaks at high-R in a spectrum is a useful indication of high symmetry and relatively long range order in surface structures.
An Oxygen K-edge NEXAFS Study of H2O Adsorption on Si(111)
Authors: Lindsay Robert , Wincott Paul L. , Muryn Christopher A. , Thornton Geoffrey , Frigo Sean P. , Simons John K. , Rosenberg Richard A.
Published: March 2014

The polarisation dependence of the oxygen K-edge Near Edge X-ray Absorption Fine Structure from Si(111)7×7-OH has been measured using synchrotron radiation. No discernible polarisation dependence is observed. This is consistent with earlier angle-resolved photoemission data and the width of the white line in indicating that the Si-OH bond is tilted away from the surface normal.
Structure Determination of Ethylene Adsorbed on Ni(100) by Multiple-Scattering Cluster Method
Authors: Feng X. S. , Tang J. C.
Published: March 2014

In this paper we present for the first time the multiple-scattering cluster calculation of the carbon Kedge NEXAFS spectra of the ethylene adsorbed on Ni(100) surface. The calculation result shows that the ethylene molecule is adsorbed at the perpendicular-bridge site and the molecular plane tilts to the surface with 50 degree. It is found that the hydrogen-nickel interaction plays an important role in the formation of the adsorption structure.
The Adsorption of O2 Molecules on Cu(100): Evidence for Enhanced Disorder and Anharmonicity
Authors: Arvanitis Dimitri , Yokoyama Toshihiko , Lederer Thomas , Comelll Giovanni , Tischer Markus , Baberschke Klaus
Published: March 2014

The structural and dynamical properties of molecular oxygen adsorbed on Cu(100) were investigated by means of O K-edge NEXAFS and SEXAFS. In an “almost-physisorbed” state, the O-O distance is 1.21 Å, the O-Cu distance is 2.05 Å, and the 2nd and 3rd cumulants of the pair distribution function (PDF), C2 and C3, are much larger than those of the atomic oxygen “precursor” state. In a “strongly-chemisorbed” state, the O-O distance is elongated to 1.45 Å, the O-Cu distance is shortened to 2.01 Å, and C2 and C3 are reduced significantly, although these values are still larger than those of the “precursor” atomic state where the O-Cu distance is 1.86 Å. For the adsorption geometry of these molecular states, a tilt model is most probable, where one oxygen atom adsorbs on the 4-fold hollow site and the other locates close to the bridge site.
Surface Structure of (√7×√7) R19.1°S/Cu(111) Studied by Surface EXAFS and Back-Reflection X-Ray Standing-Wave Method
Authors: Kitajima Yoshinori , Takata Yasutaka , Sato Hitoshi , Yokoyama Toshihiko , Ohta Toshiaki , Kuroda Haruo
Published: March 2014

Surface local structure of (√7×√7)R19.1° S/Cu(111) was studied by polarization-dependent surface EXAFS and Back Reflection X-ray Standing-Wave (BRXSW) method. A surface structure model is proposed, which satisfies both surface EXAFS and BRXSW results. It consists of three adsorption sites of sulfur atoms; 3-fold hollow site on the top copper layer, embedded site in the top layer, and 3-fold hollow site on the second copper layer. This model is consistent with the recent STM observation.
Adsorption and Decomposition of Silane on Cu(111)
Authors: Asahi Toshiyuki , Yagi Shinya , Aga Hiroji , Takata Yasutaka , Kitajima Yoshinori , Yokoyama Toshihiko , Ohta Toshiaki
Published: March 2014

The adsorption and decomposition behavior of silane (SiH4) on Cu(111) surface has been investigated by use of Si K-edge XAFS. Saturated adsorption of silane on Cu(111) at 100K produces the monolayer species, which yields a clear but fragile (√3×√3)R30° LEED pattern. The adsorbed species still has a molecular character and its Si K-XANES spectra show a significant polarization dependence. From the results of XANES and SEXAFS, it is deduced that SiH3 fragments adsorb on atop of Cu atoms with the Si-Cu distance of 2.48±0.02Å. Heating up to 300K, Si K-XAFS spectra change drastically, indicating that the adsorbed species decomposes to atomic Si to form silicide-like structure.
EXAFS Study of the Initial Interface Region Formed by Thin Zirconium and Titanium Films on Silicon(111)
Authors: Edwards A. M. , Dao Y. , Nemanich R. J. , Sayers D. E.
Published: March 2014

While titanium has long been of interest for use in creating low resistivity metal contacts on silicon, the commonly resulting epitaxial silicide (TiSi2) is often of C49 phase and is, unfortunately, metastable - transforming to the stable C54 phase at higher temperatures. Zirconium, however, only exhibits a C49 phase disilicide and, being in the same periodic group, is chemically similar to Ti, affording the possibility of alloying small quantities of Zr with Ti in order to stabilize the epitaxial C49 structure. Both Ti and Zr have been reported to show a strongly disordered interface region at low temperatures, but little quantitative structural work has been performed on the Zr:Si system. To this end, an initial structural study of the Zr on Si (111) system has been undertaken. Thin films (100Å) of Zr were deposited in UHV conditions onto atomically clean Si(111) wafers and annealed in situ at fine temperature intervals between 300 and 425°C, over which range Auger spectroscopy indicated Si diffusion to the surface. A comparison will be made with the Ti:Si system for samples of 100Å Ti prepared under the same conditions.
Polarization-dependent XAFS Measurements of Spontaneous Ordering in MOCVD-Grown Ga0.5In0.5P on GaAs Substrates
Authors: Tabor-Morris A. E. , Kemner K. M. , Bunker B. A. , Bertness K. A.
Published: March 2014

Certain thin-film alloys deposited using epitaxial growth techniques have shown spontaneous long-range ordering and band gap reduction under particular growth conditions. One such thin film is Ga0.5In0.5P grown by MOCVD on single-crystal GaAs aligned 2° from the (100) axis to achieve lattice match. Quantitative results on the gallium nearest neighbor and second nearest neighbor distances, coordination number and disorder parameters will be presented and short range structural ordering will be discussed for several ordered and disordered samples. The data reported are obtained at room and liquid nitrogen temperatures using the total electron yield detection.
Investigating the Structural Chemistry at the Interface Formed between Zinc Dialkyldithiophosphate (ZDDP) and Mild Steel Using Ultra-soft X-ray Absorption Spectroscopy
Authors: Hastie G. P. , Roberts K. J. , Adams D. , Fischer D. , Meitzner G.
Published: March 2014

Ultra-soft X-ray absorption spectroscopy at the oxygen K-, iron L- and zinc L-edges has been used to probe the structural chemistry taking place at the interface between polished mild steel in contact with lubricating oil mediated by the presence of ZDDP, an anti-wear additive. The data provides evidence for cationic exchange between Fe2+ in the substrate and Zn2+ in the ZDDP film surface adsorbed at 60°C. After decomposition at 135°C the surface layer appears zinc deficient with a chemical composition consistent with a mixture of oxide and phosphate phases.
Multiple Scattering Effects in EXAFS of CpRe(CO)3
Authors: Crüsemann R. , Fritzsche V. , Hückmann S. , Bertagnolli H.
Published: March 2014

We studied multiple scattering effects in the EXAFS of CpRe(CO)3 solved in acetone. Forward scattering at the carbon atoms of the almost linear metal-carbonyl moieties plays a dominant role. The contributions of other multiple scattering paths are nearly negligible. Multiple scattering calculations were performed using a magnetic quantum number expansion without any approximation. In order to determine structural parameters a nonlinear least square fitting was carried out on the basis of such multiple scattering calculations which include the forward scattering processes in the metal-carbonyl chains. By means of EXAFS spectroscopy no differences in the structure of CpRe(CO)3 solved in acetone and the crystallized molecule can be detected.
Glancing-Angle EXAFS Study of GaAs Oxides Grown on Polished <100> GaAs Surfaces
Authors: Proietti Maria Grazia , Ruiz Joaquin Garcia , Chaboy Jesus , Morier-Genoud François , Martin Denis
Published: March 2014

The local structure of GaAs Oxides, grown on GaAs <100> wafers by simple exposure to air after chemical etching, by heating in air at 250 °C, and at room temperature in an O3 atmosphere has been studied by Glancing-Angle X-Ray absorption spectroscopy. The oxide composition and thickness change upon the different surface treatments, varying in thickness from about 5 to 30 Å. An As enriched oxide is produced by the 30' O3 exposition while the Ga oxide component is dominant for the sample heated at 250 °C in air.
Structure of Dipivaloylmethanate Complexes Adsorbed with Hydroxyls on SiO2 Surface by EXAFS
Authors: Sekine Rika , Kawai Maki , Asakura Kiyotaka , Hikita Tokihisa , Kudo Masahiro
Published: March 2014

Adsorbed structure of copper and calcium dipivaloylmethanates [M(DPM)2, M=Cu and Ca] complexes on amorphous SiO2 are determined by extended X-ray absorption fine structure (EXAFS). There are no significant changes in the M–O bond length and the oxygen coordination numbers around M between the isolated M(DPM)2 and the adsorbed M(DPM)2. Furthermore clear existence of Cu C coordination is observed for the adsorbed Cu(DPM)2. Therefore, it is concluded that the M–O bond and the ring structure of DPM ligand remain unchanged after the adsorption. Introducing water vapor at 673 K to the Cu(DPM)2/SiO2 system results in the removal of ligand DPM from the adsorbed Cu(DPM)2. The remained species is found to be Cu metal particle by the EXAFS and the X-ray absorption near-edge strueture(XANES).
Characterization by in situ EXAFS Spectroscopy of Pt/Al2O3 and PtRe/Al2O3 Catalysts under Reaction Conditions
Authors: Caballero Alfonso , Villain Francoise , Dexpert Herve , LePeltier Fabienne , Lynch John
Published: March 2014

The effects of the catalytic reforming of n-heptane on the metallic phase of Pt/Al2O3 and PtRe/Al2O3 catalysts have been studied by EXAFS spectroscopy. In both catalysts, a new platinum carbon bond is formed during the catalytic reaction, coming from the deposition of carbonaceous residues over the metallic phase. However, in the case of the PtRe/Al2O3 catalyst this bond is formed only at lower temperature and is accompanied by important changes in the structure of the metallic particles. All these results are consistent with the existence of a PtRe intermetallic phase in the bimetallic catalyst, which intercepts more efficiently the coke precursors.
Pressure Induced Phase Transition Followed by XAFS and Multiple Scattering Calculations
Authors: Sainctavit Ph. , Itie J. P. , Polian A , Miguel A. San
Published: March 2014

We present an application of multiple scattering theory with “muffin-tin” potentials to the calculation of X-ray absorption cross section. We have measured and calculated the zinc K-edge spectra of ZnS in either zincblende or rocksalt structures. We show that some spectral features can be precisely related to the local environnement around the absorbing atom.
Au L3 XAFS Study of Ultra-Fine Gold Particles Supported on Beryllium and Magnesium Hydroxides
Authors: Kageyama Hiroyuki , Tsubota Susumu , Kamijo Hagao , Haruta Masatake
Published: March 2014

Au L3 XAFS study was made of ultra-fine gold particles supported on beryllium hydroxide (Au/Be(OH)2) and magnesium hydroxide(Au/Mg(OH)2). It is proposed that catalytic activity for CO oxidation arises from the presence of Au-Au coordination in Au/Be(OH)2 and Au/Mg(OH)2 although in the latter Au-Au and Au-O coordination coexist in the most active catalysts.
A “Cluster-in-Cluster” Structure of the SiO2-Supported PtPd Clusters
Authors: Asakura Kiyotaka , Yamazaki Yoshinao , Kuroda Haruo , Harada Masafumi , Toshima Naoki
Published: March 2014

The structures of SiO2-supported PtPd alloy clusters with the size of about 20 Å which were prepared from the PtPd colloid solutions were investigated by means of EXAFS. The phase shift and amplitude functions were derived from PtPd foils with the atomic ratio of 1:9, 1:1 and 9:1.
The curve fitting analyses showed that the PtPd clusters were present in a “cluster-in-cluster” structure in which the homogeneous clusters were composed of several smaller clusters composed of the atoms of each metal.
Structural Analysis of Polymer-Protected Pd/Rh Bimetallic Clusters by Using EXAFS Spectroscopy
Authors: Harada Masafumi , Asakura Kiyotaka , Toshima Naoki
Published: March 2014

The colloidal dispersions of the palladium-rhodium bimetallic clusters, prepared by refluxing the solution of their salts in water/ethanol in the presence of poly(N-vinyl-2-pyrrolidone) under nitrogen, are analyzed by EXAFS spectroscopy, showing that the bond distance between the Pd atom and Rh atom in the cluster is about 2.70 Å on the basis of the EXAFS measurements of the Pd/Rh alloy foils. The coordination numbers of the Pd/Rh dispersions indicate that the small particles in size mainly consist of Pd/Rh bimetallic clusters and the large particles, of palladium clusters.
Ab Initio Multiple-Scattering Calculations of the Rhenium L3 and L1 Edges XAFS in ReO3
Authors: Kuzmin Alexei , Purans Juris , Benfatto Maurizio , Natoli Calogero Renzo
Published: March 2014

We present ab initio calculations of X-ray-absorption fine structure for the Re L
3 and L
1 edges in crystalline ReO
3 based on an exact curved-wave multiple-scattering approach. We show that (1) the contribution of multiple-scattering signals from linear chains, like Re – O – Re and O – Re – O, is very large both in the L
3 and L
1-edge spectra due to the strong focussing effect caused by the middle atom; (2) the geometrical dependence of multiple-scattering terms on the final l state leads to the additional difference between signals from L
3 and L
1 edges, especially for paths forming a right angle at the absorbing atom; (3) the fine structure above L
3 and L
1-edge is a superposition of two signals from L
1 and L
2 edges with a very significant contribution of this latter.
EXAFS and Catalytic Activity of AgPt Bimetallic Cluster Supported on NaY Zeolite
Authors: Ryoo Ryong , Pak Chanho , Cho Sung June
Published: March 2014

Platinum clusters with ca. 1 nm in size have been prepared as encaged in supercages of NaY zeolite by the reduction of platinum after ion exchange of Pt(NH3)4
2+ into NaY. A series of bimetallic AgPt/NaY samples with Ag/Pt atomic ratios of 0, 0.11, 0.43 and 1.0 have been obtained by the reduction of silver after subsequent ion exchange of Ag+ into the Pt/NaY sample. The result from measurements for 129Xe NMR spectrum, and hydrogen chemisorption has indicated that the Ag atoms were put together onto the Pt cluster, with the surface enriched by Ag atoms. The extended X-ray absorption fine structure (EXAFS) of the bimetallic cluster measured above Pt L
I
I
I
and Ag K edges have been analyzed with reference EXAFS spectra which were experimentally obtained from the metal foils and those for AgPt pair which were theoretically prepared by FEFF codes distributed by Rehr et al. The catalytic activity in ethane hydrogenolysis over the AgPt bimetallic cluster has also been measured.
XAFS Studies of Platinum Supported on KL Zeolite Treated with Chlorofluorocarbon (CF3Cl)
Authors: Ishikawa Norio , Hirasawa Ken-ichi , Sugimoto Michio , Katsuno Hisashi , Hayasaka Toshiaki , Takyu Toshiyuki
Published: March 2014

The catalytic activity and selectivity for the aromatization of n-hexane of platinum supported on potassium L zeolite treated with CF3Cl (Pt/FKL) was higher than that of without CF3Cl (Pt/KL). XAFS spectra of Pt/FKL and Pt/KL catalysts, which were reduced in an in-situ cell, were collected at the L2 and the L3 edge of Pt. XANES spectra of Pt/KL catalyst showed stronger L white lines than those of Pt/FKL catalyst. The platinum clusters on FKL are more electron rich compared with those on KL. EXAFS results show that platinum atoms on KL has more interaction with oxygen of zeolite support than that on FKL. CF3Cl treatment of zeolite suppress the interaction between platinum atoms and zeolite support.
EXAFS Characterization of Rhodium-Clay Catalysts and Their Precursors
Authors: Herrero Juana , Blanco Carmen , Prieto Carlos , Dexpert Hervé , Lahoz Fernando J. , Garcia Joaquin , . .
Published: March 2014

We present here an EXAFS study of the interaction of rhodium supported on palygorskite. The precursors and catalysts have been studied together with analogously prepared silica supported catalysts.
This study suggest the formation of a covalent bond between rhodium atoms and the clay from the initial ionic interaction between the cationic rhodium complex and the structure of the clay.
Structural Characterization of Adsorbed Dinitrogen on Copper-Ion-Exchanged Mordenite through XAFS Measurements
Authors: Kuroda Yasushige , Konno Shin-ichi , Maeda Hironobu , Yoshlkawa Yuzo
Published: March 2014

X-ray absorption spectroscopy has been used to elucidate the structure of copper-ion-exchanged mordenite in the calcined state. Information about the chemical state and the local structural geometry of the exchanged copper ion has been elucidated by studing the XAXES and EXAFS spectroscopy. These findings show spectral features which would be assigned to Cu(OH)2-like species at 298 K, to CuO phase at 473 K, and to Cu(I) species at 673 K. Cu(I) species is present in an amorphous-like or microcrystalline structure. It is found that N2 molecules are adsorbed strongly on Cu(I) species and give a strong absorption band at 2299 cm-1 in infrared spectroscopy. The analysis of the EXAFS for the adsorbed N2 is performed, and demonstrates that this state is a bent type.
Structure of the Catalytic Site of a Silica-Supported Copper, Manganese Catalyst
Authors: Nomura Masaharu , Ukisu Yuji , Kazusaka Akio
Published: March 2014

The structure and the oxidation state of a copper-manganese catalyst has been clarified by means of XAFS at three stages: fresh (as-prepared), oxidized and reduced. Copper and manganese take highly dispersed structure in fresh stage. By oxidizing it, Cu–Mn, Cu…Cu and Mn…Mn interactions are formed, but there was little indication of Cu–Cu bond. Metallic copper, copper(I) oxide and manganese(II) oxide are formed in reduced stage. Through the process the valency of copper changes II→II and I→I and 0 but that of manganese was kept at II. The high catalytic activity of this catalyst can be ascribed to copper species activated by the Mn-Cu interaction but the mechanism is different from that was proposed for Hopcalite.
Na K-edge XAFS Study of Sodium Loaded on Alumina
Authors: Hasegawa Sadao , Morooka Masahiko , Aritani Hirofumi , Yoshida Hisao , Tanaka Tsunehiro
Published: March 2014

Na K-edge XAFS of Na2O/Al2O3 catalysts(4-32 wt% Na) was examined. It was deduced on the basis of XANES of sodium halides that the ionicity of an Na-O bond in catalyst sample relates to the energy position of the prominent peak at Na K-edge, which is consistent with the catalytic performance. The amount of species with the moietiy of Na-O-Al increases with an increase in Na loading up to 16 wt%. The Na-O-Na structure begins to grow from 16 wt % loading. The surface oxygen in Na-O-Al is concluded to be active species.
X-ray Absorption Studies of Supported Chromocene Ethylene Polymerization Catalysts
Authors: Zhang Guang , Auburn Pamela R. , Beach David L.
Published: March 2014

We studied the structure of two supported chromocene high density polyethylene catalysts, CrCp2 /SiO2 and CrCp2/AlPO4, by means of X-ray absorption spectroscopy using synchrotron radiation. Here Cp stands for the cyclopentadienyl group. Our results indicate that the Cr surface species of the CrCp2 /SiO2 and CrCp2/AlPO4 catalysts have similar structures around the Cr atoms regardless of the different supports. When chromocene is supported, CrCp2 loses one Cp group and anchors to the support through two Cr-O-Si ( in the case of CrCp2 /SiO2 ) or Cr-O-P ( in the case of CrCp2/AlPO4 ) bridges.
Polarization Dependence of XANES of α-Quartz: Experiments and Full Multiple-Scattering Calculations
Authors: Briois V. , Sainctavit Ph. , Flank A.-M.
Published: March 2014

The experimental spectra of α-quartz present a strong dichroic dependance at both silicon and oxygen edges. A full multiple-scattering analysis is presented at both edges.
XAFS Study with an In Situ Electrochemical Cell on Manganese Schiff Base Complexes as a Model of Photosystem II
Authors: Yamaguchi T. , Mitsunaga T. , Yoshida N. , Wakita H. , Fujiwara M. , Matsushita T. , Ikeda S. , Nomura M.
Published: March 2014

X-ray absorption fine structure (XAFS) measurements have been made on various monomeric and dimeric manganese SchifF-base complexes of different oxidation states in solid and in acetonitrile solutions. An in situ electrochemical cell was used to measure XAFS spectra for manganese complexes not available from chemical synthesis. The oxidation state and the local coordination structure of the manganese complexes have been characterized from their XANES and EXAFS spectra.
On the Active Sites of Hydrogenase from Desulfovibrio vulgaris Miyazaki F
Authors: Yasuoka Noritake , Sugiyama Shigeru , Morimoto Yukio , Hugiyama Yoshiki , Emura Shuichi , Maeda Hironobu , Koto Kichiro , Nakai Izumi , Yoshiasa Akira
Published: March 2014

An EXAFS study of hydrogenase solution has been carried out at Ni and Fe K- absorption edge. The presence of Ni atom was confirmed by the observed jump at Ni K-edge, and the ratio of the content of Ni atom and Fe atom was estimated to be 1:15 based on the ratio of the K-edge jump magnitudes. The EXAFS data at Fe K-edge were analyzed by radial distribution function. Both plausible model of Fe4S4 and Fe3S4 clusters could account for the oserved data. It is most probable that the active center of hydrogenase consists of Fe4S4 and Fe3S4 clusters and Ni atom is also included in an enzyme molecule.
Structural Changes around the Alkaline pKa of Carboxypeptidase A
Authors: Zhang K. , Auld D. S.
Published: March 2014

X-ray Absorption Fine Structure (XAFS) experiments have been performed to probe detailed structural changes at the active site of carboxypeptidase A (ZnCPD) from neutral to alkaline pHs. Direct comparison and analysis on the first coordination shells of ZnCPD revealed structural differences between pH 7.0 and pH 9.9. The observed structural changes indicated that one of the ligands to the metal moves to a 0.09 Å shorter distance from the zinc ion at the alkaline pH, resulting in a shorter metal-ligand distance and an increased first shell structural disorder. Such a situation would be expected if the water ligand of the zinc ion was converted to hydroxide at the alkaline pH.
XANES Study of Some Mixed Ligand Copper(II) Complexes
Authors: Kumawat Ramesh Chandra , Joshi Santosh Keshav , Shrivastava Basant Deo
Published: March 2014

X-ray absorption near edge structure (XANES) measurements on K-edges of copper have been made on some mixed ligand copper(II) complexes, namely, MR1=Cu-tryptophan-tyrosine; MR2=Cu-phenylalanine-tyrosine; MR2=Cu-phenylalanine-tryptophan and MR4=Cu-phenylalanine -histidine. All these ligands are biologically important and are essential amino acids. Our studies establish the order of covalency as MR1 > MR4 > MR3 > MR2. The geometry and environment in the first coordination sphere remains the same in all the systems under investigation. The changes in the values of edge-widths and other X-ray absorption parameters obtained in our studies show that a systematic change in the ligand changes the covalency. It is observed that the mixed ligands which are not the part of first coordination sphere are also important in influencing the charge content on the central metal ion. The shifts in the principal absorption maximum suggest oxidation state +2 in these complexes. The splitting of the principal absorption maximum has been interpreted.
Structure of the Different Cu Sites in the Corrugated CuO2 Plane in High Tc Superconductors
Authors: Bianconi Antonio , Longa Stefano Della , Missori Mauro , Pettiti Ida , Pompa Margherita , Soldatov Alexander
Published: March 2014

By using x-ray absorption spectroscopy different configurations of the Cu site structure in the CuO2 plane of the Bi 2:2:1:2 high Tc superconductor are found. The different Cu sites are characterized by short 2.3 Å and long 2.45 Å Cu-O(apical) distances. The linear arrays of different Cu sites forming domains with a corrugated-iron-foil shape is proposed to be a key feature of superconducting domains in the CuO2 plane. The wavelength λ of the modulation is close to the superconducting coherence length ξ and kF·λ∼2π. The ordering of the distorted Cu sites is suggested to be evidence for ordering of polarons driven by the pseudo Jahn Teller electron lattice interaction.
Local Structure of Y1-xCaxBa2Cu4O8 Determined by XAFS
Authors: Maeda Hironobu , Fujimoto Tamotsu , Kashino Setsuo , Kubozono Yoshihiro , Emura Shuichi , Murata Takatoshi , Izumi Fujio , Yamada Yu , Matsumoto Takehiko , Kodama Yasuharu
Published: March 2014

The local structure of YBa2Cu4O8 doped with Ca was studied by extended X-ray absorption fine structure (EXAFS) analysis. X-ray absorption measurements at the Ca K-edge indicate that Ca2+ ions substitute for Y3+ ions and are coordinated to eight oxide ions with a Ca–O distance of about 2.37 Å. The local structures around Ba and Cu atoms are also reported.
Polarized X-ray Absorption Fine Structure of High-Tc Superconductor; La2-xSrxCuO4 Single Crystals
Authors: Kasatani Hirofumi , Yoneda Yasuhiro , Sakaue Kiyoshi , Terauchi Hikaru , Murakami Satoshi , Kuroiwa Yoshihiro , Noda Yukio , Sugai Shunji , Hidaka Yoshikazu , Maeda Hironobu
Published: March 2014

Polarized XAFS studies of high-Tc superconductive La2-xSrxCuO4 with x=0.0, 0.09,0.1 and 0.14 were carried out over the temperature range of 15K to room temperature by the transmission method. The c-plate single crystal was used and the polarization vector of the SOR beam was perpendicular to the c-axis and the a-axis in the tetragonal system. At room temperature, polarized XANES spectrum was slightly different from the non-doped La2CuO4-y reported by Oyanagi et al.. A bond length between the copper atom and the oxygen atom was drastically changed below 60K.
Polarized Cu L Absorption spectra of Bi2Sr2Ca1-xYxCu2O8 (x=0.0, 0.6)
Authors: Nakai S. , Matsuda K. , Kamata A. , Sano K. , Noguchi K. , Ishii H. , Shiozaki I. , Arai H.
Published: March 2014

The linear polarized Cu L absorption spectra of Bi2Sr2Ca1-xYxCu2O8 (x=0.0,0.6) single crystals were measured. The polarization dependence is clearly observed in the Cu 2p
3/2 absorption peak. The energy shift between the E//c and E//ab spectra was about 0.5eV for x=0.0 and 0.3eV for x=0.6 sample. The angle-dependent X-ray photoemission spectra were also measured. The origin of the E//c component may be explained by the Pseudo-Jahn-Teller distortion of the Cu site.
Structural Studies of Some High Tc Superconducting Oxides through XANES and XPS Techniques
Authors: Saxena S. G. , Govil R. , Garg K. B.
Published: March 2014

Some structural investigations have been carried out in case of YBa2Cu3O7-x
and Bi2.2Ca2.1Sr0.7Cu2O
y
using XANES as a probe and Cu2O and CuO as reference compounds. While such studies have been performed in terms of the pre-edge structure, principal absorption maximum and shoulder structure beyond the principal absorption maximum, complementary information obtained from 2p core-level XPS of Cu has been used to ascertain charge transfer from oxygen 2p states to vacant 3d states of copper.
Polarized XANES Spectra of Quartz: Application to the Structure of Densified Silica
Authors: Lagarde P. , Flank A.-M. , Itie J.-P.
Published: March 2014

The spectra of α-quartz show intense polarisation effects which are interpreted by using geometrical considerations as shape resonances. By comparison, information on the structural effect suffered by the silica network under pressure is deduced.
Local Atomic Structure in Sb+ and Sb+/B+ Heavily Implanted Silicon from Fluorescence EXAFS
Authors: Allain J. L. , Bourret A. , Regnard J. R. , Armigliato A.
Published: March 2014

Monocrystalline silicon wafers were implanted with Sb and B ions and the Sb atomic environment was sounded by fluorescence EXAFS. After a thermal annealing it is shown that the Sb atoms form SbV2 vacancy complexes and antimony precipitates. The co-implantation with boron delays the formation of precipitates.
Relation between the Local Structure and the Desactivation of As+ Heavily Implanted Silicon
Authors: Allain J. L. , Regnard J. R. , Bourret A. , Tourillon G. , Pizzini S. , Parisini A. , Armigliato A.
Published: March 2014

Monocrystalline silicon wafers were implanted with As ions and the As atomic environment was sounded by Total Electron Yield EXAFS and fluorescence EXAFS. It is shown that the As atoms form inactive vacancy complexes at low temperature and precipitates at high temperature. The structure of these complexes and precipitates are also discussed.
The Atomic Near Neighboring Structure of Cu1-xAux Solid Solution Studied with EXAFS
Authors: Lu Lu , Kunquan Kunquan , Wu Wu , Zhonghua Zhonghua , Dong Dong , Jun Jun , Chen Chen , Xunping Xunping , Fang Fang , Zhengzhi Zhengzhi
Published: March 2014

The atomic near neighboring (NN) structure around Cu and Au in C
u
1-X

A
u

X
solid solution are investigated by using EXAFS technique. The interatomic distance of Cu-Cu, Au-Au and Au-Cu for different composition are obtained. The results demonstrate there are structural distortion and a large disorder degree of Cu atom in C
u
1-X

A
u

X
solid solution.
The Near Neighbor Atomic Arrangement in GaAsxP1-x Solid Solution
Authors: Wu Wu , Zhonghua Zhonghua , Lu Lu , Kunquan Kunquan , Dong Dong , Jun Jun , Li Li , Hefeng Hefeng , Li Li , Chenxi Chenxi
Published: March 2014

Extended X-ray absorption fine structure (EXAFS) technique is employed to probe the local atomic structure of III-V pseudobinary solid solution G
a
A
s

X

P
1-X
, with the composition from X=0 to X=1. The first and second near neighbor bond lengths and bond angles are obtained and the results imply distortion of the near neighbor atomic structure. The atomic scale structure based on a random distribution of anions can be described by using five special coordination tetrahedra, the application on G
a
A
s

X

P
1-X
is proved to be excellent agreement with the EXAFS results.
Studies of CoxMg1-xO Solid Solutions Using Laboratory EXAFS-Spectrometer
Authors: Kuzmin Alexei , Purans Juris , Sazonov Alexander , Mironova Nina
Published: March 2014

Studies of the local electronic structure and the short-range order in solid solutions Co
x
Mg1-x
O with x equal from 0.02 to 1.00 have been carried out on the Co K-edge X-ray absorption spectra measured using the laboratory EXAFS-spectrometer. A non-monotonous change of the Co-O distance in the first coordination shell with the bent at x=0.5 has been established. The second coordination shell of cobalt has been formed by cobalt and magnesium atoms with a distribution close to statistical.
Double-Electron Excitations in L-edges X-ray-Absorption Spectra of W, Ir and Cs Oxide Compounds
Authors: Purans Juris , Kuzmin Alexei , Burattini Emilio
Published: March 2014

Very strong double-electron excitations have been observed for the first time in the W, Ir L
3-edge and Cs L
1,2,3-edges X-ray-absorption spectra of tungsten and iridium oxide thin films and cesium oxide containing glasses. They are expressed as peaks with a width of several electron-volts located at the absorption background above the edge. The positions of these features are in good agreement with atomic calculations in the Z+1 approximation. They can be attributed to the transitions 2p4d → 5d5d for the L
2,3-edges and 2s4d → 6p5d for the L
1-edge with the dipole selection rules for the angular and total angular momentum ΔL=±1, ΔJ=0,±1.
EXAFS Study of Semimagnetic Semiconductors Zn1-xMnxTe: Mn 3d Electronic States and Mn-Te Local Coordination
Authors: Happo Naohisa , Sato Hitoshi , Hosokawa Shinya , Ueda Yoshifumi , Taniguchi Masaki
Published: March 2014

We have made EXAFS measurements of Zn1-xMnxTe (x≤0.65) on the Zn and Mn K-edges to investigate local environments around the Zn and Mn atoms. It is found that the Zn-Te and Mn-Te bond lengths remain almost unchanged with the variation of Mn concentration and the Mn-Te bond lengths are very close to those of Cd1-xMnxTe. These results confirm the interpretation proposed for the close similarity of Mn 3d partial density of states between Zn0.7Mn0.3Te and Cd0.8Mn0.2Te.
Using Soft X-ray Absorption Spectroscopy to Examine the Structural Changes Taking Place around Si and Al Atoms in Kaolinite Following Flash Calcination
Authors: Roberts K. J. , Robinson J. , Davies T. W. , Hooper R. M.
Published: March 2014

Structural changes associated with the flash calcination of china clay (Al2 O3 2SiO2H2 O) have been investigated using soft X-ray absorption spectroscopy (XANES and EXAFS) at the Al and Si K edges. The data reveal substantial changes to the atomic environment around the Al atomic sites with a reduction of Al-O bond distances from 1.92Å to 1.81Å associated with a change from 6 to 4 coordination. The changes in the structural environment around Si are found to be more subtle with Si remaining tetrahedrally coordinated.
Laboratory Soft X-ray XAFS: The Local Structure of K2O-SiO2 Glasses
Authors: Kamijo Nagao , Umesaki Norimasa
Published: March 2014

Using the in-laboratory XAFS facility, we have tried to determine the local structure in silicate glasses (K2O•4SiO2, K2O•3SiO2, K2O•2SiO2 and 0.2(Al2O3)0.8(K2O•4SiO2) ) respectively to elucidate the environment of modifying potassium ion which is extremely sensitive to the morphology of the network of the system. The coordination numbers of oxygen around potassium ion in K2O•2SiO2 and K2O•3SiO2 are found to be 4∼5 which is small compared with those of K2O•4SiO2 glass and crystalline nepheline ∼9. The result indicates that the introduction of potassium oxide leads to the disruption of the (SiO4) network and the formation of chain like structure or nonbridging oxygen atoms as increasing the quantity of potassium oxide. The local structures around silicon ion in some potassium silicate glasses are also compared with those of crystalline SiO2 (quartz and cristobalite).
Change of the Local Structure around Fe3+ Ion through the Heat Treatment Process in Borate Glass
Authors: Ishihara Tsuguo , Motoyama Muneyuki , Tanaka Katsuhisa , Hirao Kazuyuki , Soga Naohiro
Published: March 2014

The crystallization process of BaFe12O19 from barium iron borate glass prepared by the twin-roller quenching method has been investigated by Fe K-edge XAFS and XRD. XRD patterns revealed that at 773 K diffused diffraction peaks appeared in addition to the glass pattern, and at 873 K BaFe12O19 was crystallized. The XANES spectra changed at 773 K and resembled that of BaFe12O19 above 823 K. The Fe-O bond distances and coordination numbers derived from EXAFS spectra became closer to those of BaFe12O19 with increasing the heat treatment temperature. We found that the change of the local structure around Fe3+ ion began at 773 K and then Fe3+ ion crystallized to form BaFe12O19 above 873 K.
Structural Characterisation of Silver Ion Exchange in Alumino-Silicate Glasses
Authors: Inman J. Marie , Houde-Walter Susan N. , Greaves G. Neville , Dent Andrew J. , Dobson Barry R.
Published: March 2014

Ion exchange, which is commonly used to alter the optical and mechanical properties of glasses usually involves a one-for-one substitution of an alkali cation (Na+1) from the glass by a monovalent dopant cation (Ag+1). The structural chemistry of this process, however, is far from understood. In this study we have used XAFS spectroscopy to determine the environments of sodium in a tetrasilicate and aluminosilicate glass and also ion exchange the sodium for silver. We find that the coordination number of sodium falls in the presence of aluminium, but that this is also accompanied by an increase in site disorder. By contrast, the environment of ion exchanged silver is less disordered, the nearest neighbour coordination resembling that of Ag2O. The presence of aluminium in the glass is clearly effective in removing some of the steric constraints of mobile cations, defining preferred routes for ion exchange.
Relative Cross-Sections for Bound State Double-Electron LN-edge Transitions
Authors: Chaboy J. , Tyson T. A. , Marcelli A.
Published: March 2014

In this work, we show by explicit computation of cross sections for the allowed main line (L-edge) and double-electron (LN-edges) which transitions are expected to be observable. In addition, the excitation energies of all of these allowed transitions are given. This is carried out for Xe and elements of the sixth row of the periodic table (Cs through Rn).
An Origin of KL Absorption Edge in Si·K-XAFS
Authors: Nakano Asao , Ogata Kiyoshi , Nagashima Naoyuki
Published: March 2014

A small jump of X-ray absorption is observed at about 130eV above the a-Si:H K edge. The jump was explained as a multielectron excitation, which is identified as a Is2p→3p'ε'
p
transition. The jump is called as K
L absorption edge. XAFS spectra of a-Si, a-Si:H thin films and single crystal Si films are observed using synchrotron radiation. The energy of the jump is measured and determined as 136eV above the K edge. The observed energy suggests that the small jump of X-ray absorption indicates the existence of microcrystalline Si in the a-Si and a-Si:H thin films.
XAFS Study of SeTe in the Liquid and Solid States
Authors: Miyanaga T. , Crozier E. D. , Seary A. J. , Cutler M. , Bell F. G.
Published: March 2014

EXAFS spectra of liquid and solid SeTe are analyzed in the temperature range from 80 K to 735 K at the Te K-edge. Bond lengths of first nearest Te-Se and Te-Te are 2.59 Å and 2.83 Å in the solid state and 2.53 Å and 2.75 Å in the liquid state, respectively. The mean square relative displacement for Te-Te decreases discontinuously at the melting point.
Contribution of XAFS to the Understanding of Material Behavior under High Pressure
Authors: Itié Jean-Paul , San-Miguel Alfonso , Polian Alain
Published: March 2014

X-ray absorption spectroscopy is a powerful tool to study in situ the behavior of materials under high pressure. It provides structural information on the local environment of a given atom and its modifications under the action of pressure: bond length variation, coordination change, amorphization etc... The site specific data obtained from both XANES and EXAFS analysis are reported in comparison with other techniques (X-ray or neutron diffraction in particular) for examples from semiconductors, molecular solids, GeO2 glass. The future developments of high pressure XAFS related to the new generation of synchrotron radiation sources are discussed.