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Showing papers on "XANES published in 1996"


Journal ArticleDOI
TL;DR: In this article, Farges et al. showed that O first neighbors and alkali/alkaline-earth second neighbors around Ti contribute to the XAFS spectra, however, second neighbors are more prominent in the XANES region because the effects of disorder associated with these contributions are less important in this region than in the extended X-AFS (EXAFS) region.

287 citations


Journal ArticleDOI
TL;DR: In this paper, the location and coordination of titanium in the titanosilicate mesoporous molecular sieve MCM-41 prepared from Ti(IV) ethoxide as the source of titanium was studied by XRD, IR spectroscopy, 29Si MAS NMR, and XANES.
Abstract: The location and coordination of titanium in the titanosilicate mesoporous molecular sieve MCM-41 prepared from Ti(IV) ethoxide as the source of titanium was studied by XRD, IR spectroscopy, 29Si MAS NMR, and XANES. The results are interpreted on the basis of isomorphous substitution of Ti for Si. XANES shows that titanium is 4-coordinate and that Ti(IV) does not form a regular TiO4 tetrahedron. This is caused by the larger size of the Ti(IV) atom in comparison with Si(IV), resulting in a distortion in the silica matrix, and/or by the presence of H2O in the coordination sphere of titanium. Such distortion is consistent with the line broadening observed in the 29Si MAS NMR spectra, brought about by the wider distribution of the Si−O−Si angles in SiO4 tetrahedra as titanium is progressively incorporated in the silica matrix, and with the changes in the vibrational lattice infrared bands.

233 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the sampling depths of TEY and FY for Si L-edge and Si K-edge X-ray absorption near edge structure (XANES) spectra for SiO2 on Si substrates using total electron yield (TEY) and fluorescence yield (FY) techniques.

230 citations


Journal ArticleDOI
TL;DR: In this paper, wide angle X-ray scattering (WAXS) measurements have been made on a suite of two-line ferrihydrite (FHY2) samples containing varying amounts of coprecipitated arsenate.

202 citations


Journal ArticleDOI
TL;DR: In this paper, near-edge x-ray absorption fine structure (NEXAFS) measurements were performed on a variety of carbon materials, covering a range of hybrid bonding character from pure sp3 type to pure sp2 type.
Abstract: Near‐edge x‐ray absorption fine structure (NEXAFS) measurements were performed on a variety of carbon materials, covering a range of hybrid bonding character from pure sp3 type to pure sp2 type. Diamond, chemical vapor deposited (CVD) diamond films of varying quality. Diamond‐like carbon (DLC) films, and graphite were examined with this technique and these measurements were compared with Raman spectroscopy results and scanning electron microscopy images of carbon film morphology. For the mixed sp2 and sp3 bonded DLC materials, NEXAFS does not suffer from the large Raman cross‐section difference between sp2 and sp3 type bonds, thus allowing unambiguous characterization of carbon thin films with a broader range of sp2/sp3 bonding ratios than possible with Raman spectroscopy alone. This capability was used to determine the transition point where the sequential‐CVD carbon film growth technique produces predominately sp3 or sp2 bonded material.

150 citations


Journal ArticleDOI
TL;DR: In this paper, the temperature-programmed reduction of three Pd−Cu/KL-zeolite bimetallic catalysts has been studied using X-ray absorption near edge spectroscopy (XANES) and IR with the probe molecule CO. The authors show that complete alloying with electronic perturbation of both components (with respect to their metallic state) is reached over the full range of compositions analyzed.
Abstract: The temperature-programmed reduction of three Pd−Cu/KL-zeolite bimetallic catalysts has been studied using X-ray absorption near edge spectroscopy (XANES) and infrared spectroscopy with the probe molecule CO. We show that complete alloying with electronic perturbation of both components (with respect to their metallic state) is reached over the full range of compositions analyzed. It is also shown that the effect of reduction temperature on the nature of the surfaces exposed by the active phases, as well as the sintering processes, is primarily governed by the Pd:Cu ratio.

101 citations


Journal ArticleDOI
TL;DR: The total yield XANES spectra of 13 commonly used organic polymers have been obtained at the C K-edge using synchrotron radiation, for use as a reference source for studies on polymers as mentioned in this paper.

99 citations


Journal ArticleDOI
TL;DR: The local structural modifications resulting from chemical extraction and reinsertion of lithium in spinels of composition LiMn2O4 and Li4/3Mn5/3O4 have been investigated by X-ray absorption spectroscopy (XAS) at the manganese K-edge as discussed by the authors.
Abstract: The local structural modifications resulting from chemical extraction and reinsertion of lithium in spinels of composition LiMn2O4 and Li4/3Mn5/3O4 have been investigated by X-ray absorption spectroscopy (XAS) at the manganese K-edge. For LiMn2O4, Mn−O and Mn−Mn distances determined from the extended X-ray absorption fine structure (EXAFS) decrease significantly when lithium is extracted in 0.1 M HCl, but are restored to their original values when ∼90% of the lithium content is reconstituted by sorption in LiOH solution. The Mn−O and Mn−Mn distances for Li4/3Mn5/3O4 are shorter than for LiMn2O4, consistent with a higher manganese oxidation state and lower unit cell parameter for this compound, and show much smaller variations on lithium extraction and reinsertion. In addition lithium extraction from LiMn2O4 results in an increase in local structural order, followed by a return to the lower symmetry state of the parent material when lithium is reinserted. These changes are not observed in the spectra of Li...

94 citations


Journal ArticleDOI
TL;DR: In this article, advances in characterizing the chemical and physical properties of organic plasma deposited films (PDFs) are discussed. But the authors focus on the relationship between plasma deposition parameters and PDF properties such as surface chemistry, crosslinking, mobility, roughness, and molecular orientation.

93 citations


Journal ArticleDOI
TL;DR: In this paper, the defect content and the bonding modifications induced in BN thin films by ion implantation were studied using near-edge x-ray absorption fine structure (NEXAFS).
Abstract: Near‐edge x‐ray absorption fine structure (NEXAFS) has been used to study the defect content and the bonding modifications induced in BN thin films by ion implantation. The initial films were hexagonal‐like BN grown on Si(100) by pulsed laser deposition. Subsequent ion implantation with N2+ at 180 keV induces the formation of a significant proportion of sp3 bonding (cubic‐like), and the formation of nitrogen void defects in the remaining sp2 BN. These modifications in the bonding of a film lacking long range order can only be distinguished with a local order technique like NEXAFS.

91 citations


Journal ArticleDOI
TL;DR: In this article, the S L-edge X-ray absorption near edge structure (XANES) spectra of several inorganic and organic sulphur model compounds are presented.

Journal ArticleDOI
TL;DR: In this paper, the dispersion of Ni ions in these samples has been studied by X-ray diffraction (XRD), Xray photoelectron spectroscopy (XPS), and Xray absorption fine structure (XAFS), showing that the atomic concentration of Ni and Mg against the depth is almost constant and close to those of bulk concentrations.
Abstract: NiO−MgO samples (NixMg1-xO:x = moles of Ni/(moles of Ni + moles of Mg)) were prepared by impregnation of MgO powder with an aqueous solution of Ni(NO3)2, followed by calcination at 773 K. The dispersion of Ni ions in these samples has been studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS). XPS of the depth profile of the samples shows that the atomic concentration of Ni and Mg against the depth is almost constant and close to those of bulk concentrations. The analyses by EXAFS and XANES reveal the absence of the preferential segregation of nickel oxide phase or magnesium oxide phase in all samples, suggesting the substitution of Ni ions for Mg ions. A detailed analysis by the curve-fitting method indicates that Ni ions dissolving into MgO are dispersed at random, regardless of the compositions of the samples. These results suggest that these samples form solid solutions over the entire composition range, even by calcination at 773 K.

Journal ArticleDOI
29 May 1996-Langmuir
TL;DR: In this paper, a review of the literature for the metal interaction with polyimide surfaces is presented, with a special emphasis on the interaction of metals with a polyimides surface at very low metal coverages.
Abstract: In this article we briefly review the literature for the evaporated metals gold, silver, copper, palladium, chromium, and potassium on polyimide surfaces and compare these previous results to newer experiments using Fourier transform infrared reflection absorption spectroscopy (FT-IRAS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). The polyimide films were prepared by vapor phase deposition. Metal coverages range from submonolayer to several monolayers, but special emphasis in this work is put on the interaction of metals with a polyimide surface at very low metal coverages. Before our new results are presented, we discuss the various chemical and nonchemical effects, which can contribute to the change in IR absorption of polymers. For all of the metals except potassium only attenuation of polymer IR bands is observed. For the metal deposits of Au, Cu, Ag, and Pd the attenuation of the IR bands can be explained by a purely physical interaction mechanism, i.e., dynamical dipole scree...

Journal ArticleDOI
TL;DR: In this paper, a structural analysis of Mo−Mg binary oxides in oxidized/reduced states was carried out and it was concluded that MoO4 tetrahedra are the main component in the near-surface region for samples of x (Mo/(Mo + Mg)) ≤ 0.7 in the oxidized state, while the reduced Mo ions including MoO2 species are also formed.
Abstract: Mo L3-edge XANES and diffuse reflectance UV−vis spectra have been recorded for structural studies of Mo−Mg binary oxides which catalyze metathesis reactions of olefins after pretreatment with H2 at 773 K. The XANES of reference compounds revealed that the local symmetry around the Mo ion as well as the valence state affects the spectral features. From the XANES of Mo−Mg binary oxides in oxidized/reduced states, it is concluded that MoO4 tetrahedra are the main component in the near-surface region for samples of x (Mo/(Mo + Mg)) ≤ 0.7 in the oxidized state. For samples in the reduced state, the tetrahedral species remain, but reduced Mo ions including MoO2 species are also formed, while the MoO2 phase is formed in the bulk phase at x = 0.5−0.8. In the latter samples, Mo ions are easily reduced by treatment with H2. The active species for metathesis reactions relates to formation of the MoO2 phase not only in the bulk but also in the near-surface region.

Journal ArticleDOI
TL;DR: In this article, the authors characterized the preparation of AuCln in Na−Y zeolite by means of X-ray diffraction (XRD), ultraviolet diffuse reflectance (UV−vis), Au LIII-edge Xray absorption near-edge structure (XANES), and extended X-Ray absorption fine structure (EXAFS).
Abstract: Preparations of AuCln in Na−Y zeolite were characterized by means of X-ray diffraction (XRD), ultraviolet diffuse reflectance (UV−vis), Au LIII-edge X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS). Au2Cl6 was first homogeneously dispersed on the zeolite surface by mechanical mixing at room temperature under a nitrogen atmosphere. The thermal evacuation of the mixed sample at 323 K for 72 h led to the eruption of a sole Au2Cl6 crystalline line at 2θ = 14.70° due to the condensation of the gold species on the zeolite surface. The detected Au−O bond by the EXAFS technique has a coordination distance of 2.16 A, which is about the same as that registered for the tetrameric molecule of dimethylgold(III) hydroxyl. Ramping the Au2Cl6−Na−Y reaction temperature to 338 K yielded appreciable amounts of Au(I) ions which were embedded with the Cl- ions in a (AuCl)n zig-zag-like structure. The Au−O interactions were not apparent due to the removal of OH attached to Au(I...

Journal ArticleDOI
TL;DR: In this article, a detailed picture of the local atomic environment of titanium in the novel titanosilicate ETS-10 has been derived from X-ray absorption spectroscopy aided by lattice energy minimization calculations.
Abstract: A detailed picture of the local atomic environment of titanium in the novel titanosilicate ETS-10 has been derived from X-ray absorption spectroscopy aided by lattice energy minimization calculations. It is revealed that, in contrast to previous structural models for this disordered material, titanium exists in a distorted octahedral environment with long and short Ti−O bonds distributed within the chains of TiO6 octahedra. Plausible models for the extraframework cation distribution have also been proposed.

Journal ArticleDOI
TL;DR: In this article, the coordination environment of Ti in a variety of Ti-oxide model compounds and five fresnoites (crystalline and glassy Ba2TiOSi2O7, Sr2T iOSi2o7, Ba2TiOGe2O 7, Ba 2TiOeOe7 and Ba OeOo7) has been measured using high-resolution X-ray absorption near edge structure (XANES) spectroscopy at the Ti K-edge at ambient temperature and pressure.
Abstract: The coordination environment of Ti in a variety of Ti-oxide model compounds and five fresnoites (crystalline and glassy Ba2TiOSi2O7, Sr2TiOSi2O7 and Ba2TiOGe2O7) has been measured using high resolution X-ray absorption near edge structure (XANES) spectroscopy at the Ti K-edge at ambient temperature and pressure. Five-coordinated Ti, [5]Ti, is the dominant Ti species (≈ 60% of the total Ti atoms) in the two glassy fresnoites studied. However, [4]Ti and [6]Ti were also detected (∼ 20% of the total Ti atoms each). Both glassy fresnoites (silicate and germanate) show the same amounts of [4]Ti, [5]Ti and [6]Ti. [5]Ti is most likely present as square planar, titanyl-bearing moieties. Based on thermal expansion models around [5]Ti in crystalline fresnoite, some breakage in the square planar units (and the formation of [4]Ti and [6]Ti by disproportionation) may be responsible for the presence of these three Ti-coordinations in the melt phase (and, consequently, in the glassy modifications).

Journal ArticleDOI
TL;DR: In this article, full multiple-scattering calculations at the aluminium K edge were performed with experiments for four crystalline silicates and oxide minerals, showing that aluminium atoms are either fourfold or sixfold coordinated to oxygen atoms in Al sites that are poorly symmetric.
Abstract: We present full multiple-scattering calculations at the aluminium K edge that we compare with experiments for four crystalline silicates and oxide minerals. In the different minerals aluminium atoms are either fourfold or sixfold coordinated to oxygen atoms in Al sites that are poorly symmetric. The calculations are based on different choices of one-electron potentials according to aluminium coordinations and crystallographic structures of the compounds. Hence it is possible to determine how the near-edge spectral features are a sensitive probe of the effective potential seen by the photoelectron in the molecular environment. The purpose of this work is to determine on the one hand the relation between Al K-edge spectral features and the geometrical arrangements around the aluminium sites, and on the other hand the electronic structure of the compounds.

Journal ArticleDOI
TL;DR: In this paper, an air-stable Ge(111) surface can be made by wet chemical HCl treatment in ambient atmosphere using X-ray photoelectron spectroscopy (XPS) and photon electrical field polarization-dependent Cl K-edge x-ray absorption spectrography (XANES).
Abstract: It is shown that an air‐stable Ge(111) surface can be made by wet chemical HCl treatment in ambient atmosphere. X‐ray photoelectron spectroscopy (XPS) and photon electrical field polarization‐dependent Cl K‐edge x‐ray absorption spectroscopy (XANES) were used to study the chemical structure and the physical orientation of chemisorbed Cl. It is found that Cl forms a monovalent bond with the Ge(111) dangling bond (DB) along 〈111〉 surface normal. The stability of HCl‐treated Ge(111) is attributed to the surface DBs being terminated by monochloride. Thermodynamics are found to be the governing force in the Ge–HCl reaction processes.

Journal ArticleDOI
TL;DR: In this article, a correlation between the co-ordination numbers of the first, second and third Si neighbor shells from Fourier transform fitting of EXAFS and both emission peak energies and optical band gaps estimated by PLE (photoluminescence excitation dependence) suggests that the nanostructures of the newly produced red, yellow and green emitting porous Si specimens are nanowires, rather than nanocrystalline.
Abstract: Freshly produced red, yellow and green emitting porous Si specimens have been studied by NEXAFS and EXAFS (near edge and extended x‐ray absorption fine structure). The emission peaks are at 690, 580, and 520 nm, which almost covers the full visible range that direct anodization can achieve. The correlation between the co‐ordination numbers of the first, second and third Si neighbor shells from Fourier transform fitting of EXAFS and both emission peak energies and optical band gaps estimated by PLE (photoluminescence excitation dependence) suggests that the nanostructures of the PS are nanowires, rather than nanocrystalline. Two types of quantum nanowire with one and one‐plus‐a‐fraction dimensionality are proposed to interpret the correlation. The order factors of the theoretical fits suggest the nanowires of the freshly produced PS have crystalline cores.

Journal ArticleDOI
TL;DR: In this paper, the authors applied the near-edge x-ray absorption fine structure (NEXAFS) technique to characterize the systematic trends in the oxygen K edge and metal L edge features of powder materials of 3D transition metal oxides.
Abstract: We have applied the near‐edge x‐ray absorption fine structure (NEXAFS) technique to characterize the systematic trends in the oxygen K edge and metal L edge features of powder materials of 3d transition metal oxides. In agreement with previous high energy electron energy loss spectroscopy data [L. A. Grunes et al., Phys. Rev. B 25, 7157 (1982)], our NEXAFS results demonstrate that the characteristic oxygen K‐edge features are related to the number of d electrons in the transition metal oxides. By comparison with these model compounds data, we have applied NEXAFS to investigate the compositions and reactivities of thin oxide overlayers on several single crystal surfaces, including V(110), Mo(110), and Ni(100). We will use several examples to demonstrate the capabilities of NEXAFS, such as the determination of surface O/M stoichiometries, the differentiation between atomic and molecular oxygen species on surfaces, and the determination of reaction kinetics under in situ conditions. Finally, direct different...

Journal ArticleDOI
TL;DR: The reduction of TiBr4·2THF using K[BEt3H] yields the hydrogen-free organosol Ti·0.5THF as mentioned in this paper, which consists of very small Ti particles in the zerovalent state.
Abstract: The reduction of TiBr4·2THF using K[BEt3H] yields the hydrogen-free organosol Ti·0.5THF. According to the HRTEM (high-resolution transmission electron microscopy), EDX (energy-dispersive X-ray) fluorescence, XPS (X-ray photoelectron spectroscopy), XANES (X-ray absorption near edge structure), and EXAFS (extended X-ray absorption fine structure) data, this nanoparticulate metal colloid consists of very small Ti particles in the zerovalent state, stabilized by intact THF molecules.

Journal ArticleDOI
TL;DR: Investigations have shown, in agreement with earlier literature results of multiple-scattering theory, that the distribution of unoccupied p-like states around cation atoms is mainly determined by the type of anion and does not depend significantly on the M concentration.
Abstract: Systematic studies of x-ray-absorption near-edge structure (XANES) at the K edge of cations and anions in ZnS, ZnSe, and ZnMS and ZnMSe compounds, with M being a transition metal (Mn, Fe, Co, Ni), were performed. Our investigations have shown, in agreement with earlier literature results of multiple-scattering theory, that the distribution of unoccupied p-like states around cation atoms is mainly determined by the type of anion and does not depend significantly on the M concentration. Three peak structures can be found in the cation K-edge XANES of the sulphides, whereas a two-peak structure is observed in selenides. The effective charge transfer for the M cation was estimated within 2--2.5e, from measured chemical shifts of the respective K edges. Additionally, direct evidence of hybridization between the states of M and p states of S was found from S K-edge XANES studies. The empirical correlation between the shape of M K edges and the solubility limit of M in the investigated solid matrices was revealed. \textcopyright{} 1996 The American Physical Society.

Journal ArticleDOI
TL;DR: In this paper, the chemical shift of the B K-edge is correlated with the oxidation state of B, electronegativity of ligand and coordination geometry of B. The coordination of B in K 2 OSiO 2 B 2 O 3 glasses is also investigated.

Journal ArticleDOI
TL;DR: In this article, the authors measured Pt L 2,3 -edge X-ray absorption near edge structure (XANES) spectra for the Pt particles supported on SiO 2, Al 2 O 3 and MgO with and without adsorbed hydrogen.

Journal ArticleDOI
TL;DR: In this paper, the reaction between colloidal palladium and cupric acetate in 2-ethoxyethanol leads sequentially to the reduction of Cu(II) to Cu(0) at the surface of the palladium particle and dissolution of the deposited copper in the matrix.
Abstract: The reaction between colloidal palladium and cupric acetate in 2-ethoxyethanol leads sequentially to the reduction of Cu(II) to Cu(0) at the surface of the palladium particle and dissolution of the deposited copper in the palladium matrix. The reaction was monitored by infrared spectroscopy using carbon monoxide adsorbed on samples of the colloid during the reaction and by X-ray absorption spectroscopy (NEXAFS and EXAFS) on the colloidal metal after completion was reached. The Cu K near-edge X-ray absorption spectrum shows reduction of Cu(II) to Cu(0). After deposition on the palladium surface the copper is zerovalent, and subsequently it migrates into the palladium particle but only to within a few atomic layers of the surface.

Journal ArticleDOI
TL;DR: In this article, in situ X-ray absorption near edge structure (XANES), ESR, photoluminescence, and diffuse reflectance (DR) spectroscopy were applied to examine the Ag+/ZSM-5 catalyst.
Abstract: Over Ag+/ZSM-5 catalyst prepared by an ion-exchange the photocatalytic decomposition of NO into N2, N2O, and NO2 was affected by UV irradiation at a low temperature of 298 K. In situ X-ray absorption near edge structure (XANES), ESR, photoluminescence, and diffuse reflectance (DR) spectroscopy were applied to examine the Ag+/ZSM-5 catalyst. The wavelengths of the effective UV irradiation was determined. Data suggest that electron transfer from excited Ag+ ion into the π anti-bonding molecular orbital of NO molecule plays a significant role in the photocatalytic decomposition of NO.

Journal ArticleDOI
TL;DR: In this article, a series of Pd-Cu/KL zeolites with varying Pd : Cu ratios have been studied by a combination of FTIR and XANES.

Journal ArticleDOI
TL;DR: In this article, the authors used X-ray absorption spectroscopy (XAS) to obtain the valence states, bond lengths, and coordination numbers of the metal ion.
Abstract: MCM-41 type mesoporous silicas have been prepared in which one or more of the following elements are accommodated in framework sites: titanium, iron, chromium, vanadium, manganese, boron and aluminium. XRD and FTIR are used as aids to characterisation, which is achieved chiefly — and to a degree that arrives at valence states, bond lengths and coordination numbers of the metal ion — by X-ray absorption spectroscopy (XAS). Ti-containing MCM-41, as well as the Fe-, V- and Cr-containing variants, yield self-consistent, XAS-based, structural data of the respective metal-ion sites. Some of these (especially those containing Ti) are exceptionally good catalysts for the selective oxidation of large organic molecules such as limonene and norbornene.

Journal ArticleDOI
TL;DR: In this article, Nagamori et al. showed that commercially available solid silicon monoxide is not really silicon(II)oxide, but a composite of at least two compounds.
Abstract: By XANES- and 29Si-MAS-NMR-spectroscopy, evidence has been obtained that commercially available solid silicon monoxide is not really silicon(II)oxide. Instead, this SiO seems to be a composite of at least two compounds. This is in contrast to a previous report in this Journal [M. Nagamori, J.-A. Boivin and A. Claveau, J. Non-Cryst. Solids 189 (1995) 270].