Showing papers on "XANES published in 2002"
TL;DR: The results illustrate the complex role played by O vacancies in the mechanism for reduction of an oxide and show a direct NiO-->Ni transformation without accumulation of any intermediate phase.
Abstract: Reduction of an oxide in hydrogen is a method frequently employed in the preparation of active catalysts and electronic devices. Synchrotron-based time-resolved X-ray diffraction (XRD), X-ray absorption fine structure (NEXAFS/EXAFS), photoemission, and first-principles density-functional (DF) slab calculations were used to study the reaction of H2 with nickel oxide. In experiments with a NiO(100) crystal and NiO powders, oxide reduction is observed at atmospheric pressures and elevated temperatures (250−350 °C), but only after an induction period. The results of in situ time-resolved XRD and NEXAFS/EXAFS show a direct NiO→Ni transformation without accumulation of any intermediate phase. During the induction period, surface defect sites are created that provide a high efficiency for the dissociation of H2. A perfect NiO(100) surface, the most common face of nickel oxide, exhibits a negligible reactivity toward H2. The presence of O vacancies leads to an increase in the adsorption energy of H2 and substanti...
321 citations
TL;DR: In this paper, a pseudopotential scheme for calculating X-ray absorption near-edge structure (XANES) spectra is presented. But the method is applied to the carbon K edge in diamond and to the silicon and oxygen K edges in $\ensuremath{\alpha}$-quartz for which polarized XANES spectra were measured.
Abstract: We present a reciprocal-space pseudopotential scheme for calculating x-ray absorption near-edge structure (XANES) spectra. The scheme incorporates a recursive method to compute absorption cross section as a continued fraction. The continued fraction formulation of absorption is advantageous in that it permits the treatment of core-hole interaction through large supercells (hundreds of atoms). The method is compared with recently developed Bethe-Salpeter approach. The method is applied to the carbon K edge in diamond and to the silicon and oxygen K edges in $\ensuremath{\alpha}$-quartz for which polarized XANES spectra were measured. Core-hole effects are investigated by varying the size of the supercell, thus leading to information similar to that obtained from cluster size analysis usually performed within multiple scattering calculations.
292 citations
TL;DR: In this article, the authors explored the chemical sensitivity of these features in C 1s and O 1s NEXAFS spectra for a series of polymers containing the carbonyl group in a range of different bonding environments.
Abstract: Carbonyl core (C 1s, O 1s) → π*CO transitions are distinctive in the near-edge X-ray absorption fine structure (NEXAFS) spectra of species containing carbonyl groups. These features are used for the chemical microanalysis of organic materials using X-ray microscopy. We have explored the chemical sensitivity of these features in C 1s and O 1s NEXAFS spectra for a series of polymers containing the carbonyl group in a range of different bonding environments. Ab initio calculations are used to explain the origin of the observed trends and to explore the effect that orbital interactions have on the energy of these core (C 1s, O 1s) → π*CO features. The differences between the experimental and the calculated carbonyl core (C 1s, O 1s) → π*CO transition energies are systematic and can be used to develop a semiempirical method for predicting the absolute (experimental) transition energies from the calculated transition energies. This relationship is applied to a large body of calculated transition energy data to ...
279 citations
TL;DR: In this article, a binder-free Li-ion deintercalated Li 1 - x CoO 2 film was made using the electrostatic spray deposition (ESD) technique.
Abstract: To investigate the electronic structure of the electrochemically Li-ion deintercalated Li 1 - x CoO 2 system, soft X-ray absorption spectroscopy (XAS) for the oxygen K-edge and the Co L I I , I I I -edge has been carried out intensively with compositional x value variation, compared with Co K-edge X-ray absorption near edge structure (XANES) spectroscopy. To get reasonably good XAS spectra for the electrochemically Li-ion deintercalated Li 1 - x CoO 2 system, we made a binder-free LiCoO 2 film electrode using the electrostatic spray deposition (ESD) technique. The oxygen K-edge XAS for Li 1 - x CoO 2 shows more effective spectral change with respect to Li-ion content than the Co L I I , I I I -edge XAS. The dependence of the absorption peak feature on the Li content is described in terms of the ground state of the Co and O atoms, showing the systematic variation of the hole-state site distribution between Co and oxygen atoms. From the Co L I I , I I I -edge XAS, it is found that the broad peak shift to higher energy with the Li-ion deintercalation is due to rehybridization between Co and O atoms under the local structural distortion of CoO 6 octahedra, which is also confirmed by the formation of two additional absorption peaks below the threshold energy corresponding to the oxygen 2p hole state hybridized with the 3d orbital of Co ion in the distorted CoO 6 octahedral site. In the O K-edge XAS spectra for the deintercalated Li 1 - x CoO 2 film, the shoulder absorption peak in the energy region higher than the threshold energy could be assigned to the higher oxidation state of the oxygen site on Li deintercalation. From the Co L I I , I I I -edge and O K-edge XAS results for the Li-ion deintercalated Li 1 - x CoO 2 film, it is concluded that the charge compensation for the Li-ion deintercalation process could be achieved mainly in the oxygen site and Co metal atomic site simultaneously. O K-edge and Co L I I , I I I -edge XAS results for cycled LiCoO 2 film show that the capacity fading of the LiCoO 2 system is related to the decrease of Co-O bond covalency by the local structural distortion of CoO 6 octahedra remaining in the cycled LiCoO 2 .
272 citations
TL;DR: In this article, the structure of Fe2O3 nanoparticles with different sizes were investigated using Fe K-edge X-ray absorption near-edge structure (XANES) and the FEFF calculations, as well as surface modification with enediol ligands.
Abstract: The structures of Fe2O3 nanoparticles with different sizes were investigated using Fe K-edge X-ray absorption near-edge structure (XANES) and the FEFF calculations, as well as surface modification with enediol ligands. The studies not only revealed the existence of under-coordinated Fe sites in the nanoparticles but also confirmed that these under-coordinated sites were located on the surface. Upon binding of enediol ligands, surface sites were restructured to octahedral sites. In particular, the nature of the surface defects and their correlation with the unique properties of the nanoparticles were discussed. Model calculations were conducted for FemOn (m ≥ 1, n ≥ 4) clusters of various sizes centered at Fe sites with octahedral (Oh), distorted octahedral (C3v) and tetrahedral (Td) coordination geometry using FEFF8.10 programs. The main features of the calculated spectra agree with the experimental results and were correlated to the density of states, the Fe coordination geometry, and the long-range orde...
240 citations
TL;DR: In this article, the structural and optical properties of the blue phosphor were investigated as a function of the europium concentration in BaMgAl10O17 using the neutron and the X-ray powder diffraction methods and luminescence and Xray absorption near-edge structure (XANES) spectroscopies.
Abstract: BaMgAl10O17:Eu2+ phosphors are synthesized by solid-state calcining of BaCO3, Al2O3, MgO, and Eu2O3 with AlF3 as a flux. The structural and optical properties of the blue phosphor are investigated as a function of the europium concentration in BaMgAl10O17 using the neutron and the X-ray powder diffraction methods and luminescence and X-ray absorption near-edge structure (XANES) spectroscopies. The unit cell parameters of BaMgAl10O17:Eu2+ blue phosphor are calculated through the Rietveld refinements of the X-ray and neutron diffraction data. In addition, the maximum electron energy density of the phosphor is calculated using the maximum entropy method to reveal the overall structural changes in BaMgAl10O17 and BaMgAl10O17:Eu2+. The critical concentration is estimated from the concentration dependencies of the absolute quantum efficiency and the intensity of the photoluminescence. The XANES spectrum reveals that nonsubstituted Eu ions exist in the trivalent state above the critical concentration.
226 citations
TL;DR: In this article, the C (carbon) K edge near-edge X-ray absorption (NEXAFS) spectra of all 20 amino acids commonly occurring in nature were analyzed.
Abstract: We present comprehensive measurements of the C (carbon) K edge near-edge X-ray absorption (NEXAFS) spectra of all 20 amino acids commonly occurring in nature. Qualitative trends among the spectra of amino acids with similar chemical character are identified and spectral features are compared with extensive ab initio calculations. The contributions of individual units and substitutional groups have been determined to explore their fingerprinting character using the building block concept. Several such units are found. Two that give particularly clear features in the C Is NEXAFS spectra are the carboxyl group (which can be clearly identified by a pronounced structure due to the C 1s-->pi*c-o transition with maximum at 288.65(5) eV) and modified phenol rings in aromatic amino acids (which give sharp C 1s-->pi*c=o structures). The latter transitions are located around 285 cV, and their shape is specific for each aromatic amino acid. Other building blocks, such as the CNHn group and the CH, CC, CO, CN pair bonds, are also identified, although their characteristic features are less pronounced in the C K edge spectra than the carboxylic and aromatic structures. This study provides the basis for rigorous assignment of the NEXAFS spectra of the amino acids, and will be helpful in developing X-ray absorption spectroscopy for quantitative analysis of proteins.
211 citations
TL;DR: In this article, the physical and chemical effects of soft X-ray irradiation of polymers have been systematically evaluated for photon energies just above the C 1s binding energy, and a method for quantifying this radiation damage was proposed to characterize the loss of mass and loss of carbonyl group functionality.
197 citations
TL;DR: In this article, the electronic structure, chemical states and local geometry of the active species in the CuO/ZnO/Al2O3/ZrO2 multicomponent mixed oxide catalysts employed in the oxidative steam reforming of methanol (OSRM) reaction for H2 production were investigated.
Abstract: Systematic X-ray photoelectron spectroscopy (XPS), X-ray induced Auger electron spectroscopy (AES), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies were undertaken to investigate the electronic structure, chemical states and local geometry of the active species in the CuO/ZnO/Al2O3/ZrO2 multicomponent mixed oxide catalysts employed in the oxidative steam reforming of methanol (OSRM) reaction for H2 production. The core level XPS and AES indicated the existence of CuO and ZnO-like species. Two kinds of zirconium species, one similar to that of ZrO2 and another with relatively higher electron density were noticed from the Zr 3d core level XPS of Zr- containing catalysts. The valence band (VB) XPS studies revealed that for Zr-containing catalysts, the Cu 3d anti-bonding orbital splits from the main
VB and shifts toward lower binding energy (BE). The surface Cu/(Al + Zr) ratios were found to be close to those in the bulk while segregation of Zn at the surface was evidenced in all samples. The XANES and EXAFS results also indicated the existence of CuO and ZnO-like species, whose local environments are modified with respect to the chemical composition. The EXAFS study of the Zr-containing catalysts indicated the existence of a “Cu–O–Zr” bonding with a Cu–Zr distance in the range 3.5 to 3.9 A. The results indicated the existence of a Cu–Zr synergistic interaction in these catalysts which improved the catalytic performance in the OSRM reaction
175 citations
TL;DR: In this paper, a wide range of techniques were used to characterize the catalysts: high-resolution TEM and X-ray photoelectron spectroscopy, as well as high-energy diffraction (HED) and x-ray absorption spectroglobalization (XANES and EXAFS) using synchrotron radiation.
175 citations
TL;DR: In situ X-ray absorption spectroscopy (XAS) of the Mn and Ni K-edges and 6 Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) was carried out during the first charging and discharging process for the layered LiNi 0.5 Mn 0. 5 O 2 cathode material as discussed by the authors.
Abstract: In situ X-ray absorption spectroscopy (XAS) of the Mn and Ni K-edges and 6 Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy have been carried out during the first charging and discharging process for the layered LiNi 0 . 5 Mn 0 . 5 O 2 cathode material. The Ni K-edge structure in the X-ray absorption near-edge structure (XANES) spectrum exhibits a rigid positive energy shift with increased Li deintercalation level, while the Mn XANES spectra do not show any substantial energy changes. The Ni edge shifts back reversibly during discharge. Further Li-ion intercalation at ∼1 V (vs. Li) could be accomplished by reduction of the Mn 4 + ions. The 6 Li MAS NMR results showed the presence of Li in the Ni 2 + /Mn 4 + layers, in addition to the expected sites for Li in the lithium layers. All the Li ions in the transition metal layers are removed on the first charge, leaving residual lithium ions in the lithium layers.
TL;DR: In this paper, gold clusters on the surface of MgO powder (calcined at 673 K) were prepared from adsorbed [Au(CH3)2(acac), where acac is C5H7O2] and characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy.
Abstract: Gold clusters on the surface of MgO powder (calcined at 673 K) were prepared from adsorbed [Au(CH3)2(acac), where acac is C5H7O2] and characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray absorption near edge spectroscopy (XANES). One sample initially contained gold predominantly in the form of clusters approximated as Au6 on the basis of the EXAFS data showing first- and second-shell Au−Au coordination numbers of 4.0 ± 0.4 and 1.0 ± 0.1, respectively. The other sample initially contained larger clusters, with an average diameter of about 30 A (containing about 100 atoms each, on average), as shown by the EXAFS first- and second-shell Au−Au coordination numbers of 9.4 ± 0.9 and 3.5 ± 0.4, respectively. The samples, in each of the three gases CO, O2, and He and in the presence of CO + O2 during CO oxidation catalysis, were investigated by EXAFS spectroscopy and XANES in a cell that was also a flow reactor. Data obtained during steady-state CO oxidation indicate the presen...
TL;DR: In this paper, the structure of transparent (1−x)TeO2-xWO3 glasses with 0≤x≤0.325 mol were synthesized by the fast quenching technique.
TL;DR: In this paper, the authors combined synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy, extended Xray absorption fine structure (EXAFS) and binding affinity studies to determine the coordination, geometry, and strength of methyl mercury, CH3Hg (II), bonding in soil and stream organic matter, and determined the sum of concentrations of highly reduced organic S groups (designated Org-SRED), such as thiol (RSH), disulfane (RSSH), sulfide (RSR),
TL;DR: In this paper, the orientation of the FAS molecules was investigated with polarization-dependent X-ray absorption near edge spectroscopy (XANES), and the molecular structure was calculated in order to aid in the interpretation of the polarization dependence of the XANES spectrum at F K-edge.
Abstract: Fluoroalkylsilanes (FAS) prove to be an interesting water-repellent coating for the recently discussed “superhydrophobic surfaces”. The FAS investigated here form a self-assembled monolayer when brought into contact with a surface. They arrange at a high degree of orientation with their molecular axis perpendicular to the substrate surface. The film stability and the film thickness were observed using X-ray photoelectron spectroscopy. The orientation of the FAS molecules was investigated with polarization-dependent X-ray absorption near edge spectroscopy (XANES). Furthermore using density functional theory the molecular structure was calculated in order to aid in the interpretation of the polarization dependence of the XANES spectrum at F K-edge.
TL;DR: A theoretical study of the sensitivity of Pt L3 x-ray absorption near edge structure (XANES) to the size and shape in small Ptn clusters is reported in this paper, based on a full multiple scattering, self-consistent field, real space Green's function approach implemented in the ab initio FEFF8 code.
Abstract: A theoretical study of the sensitivity of Pt L3 x-ray absorption near edge structure (XANES) to the size and shape in small Ptn clusters is reported. Calculations, based on a full multiple scattering, self-consistent field, real-space Green’s function approach implemented in the ab initio FEFF8 code, show that XANES provides a characteristic signature of cluster shape. For example, the calculated white line intensity exhibits a large variation for small cluster sizes and geometry, but becomes independent of cluster size for large clusters. A strong polarization dependence of the white line is predicted for two-dimensional clusters. For three-dimensional clusters the polarization dependence is smaller, but can be used as a measure of the “flatness” of a cluster. A series of semirelativistic all-electron, full potential density functional calculations was also performed for several Ptn clusters. These calculations show the existence of intrinsic static disorder in these clusters due to nonisotropic shrinkag...
TL;DR: An overview of the XANES technique contribution to the analysis of multicomponent catalysts can be found in this paper, where the theoretical basis of the technique, the interpretation of the energy position and intensity, and the numerical methods developed to interpret X-ANES data on catalytic systems are described and discussed.
Abstract: The article gives an overview of the XANES technique contribution to the analysis of multicomponent catalysts. The theoretical basis of the technique, the interpretation of the energy position and intensity of XANES features, and the numerical methods developed to interpret XANES data on catalytic systems are described and discussed in the first part. In the second part, the most recent XANES studies of catalytic samples are reviewed, giving particular attention to the solid state chemistry information extracted under real, in-situ conditions. This concerns structural and redox properties of the systems during preparation stages, activation treatments like reduction, oxychlorination, or sulfidation, and reaction conditions. Additional effort was made to describe the use of XANES to gain insight on electronic properties of catalysts. The influence of all these redox, geometrical and electronic properties on catalytic behavior, particularly as a function of particle size and active metal-support in...
TL;DR: XAS (X-ray absorption spectroscopy) has proven to be a powerful technique in several fields including the biological and environmental sciences as discussed by the authors, where the use of other methods is time consuming, cumbersome, and can lead to false results.
Abstract: XAS (X-ray absorption spectroscopy) has proven to be a powerful technique in several fields including the biological and environmental sciences. It has enabled scientists to analyze samples that could not be analyzed using classical techniques such as XRD (X-ray diffraction). In addition, it allows for the direct determination of elemental oxidation states, where the use of other methods is time consuming, cumbersome, and can lead to false results. XAS experimentation has allowed the direct determination of the local coordination environments in many different samples. This review article briefly explains some of the concepts related to two of the most important techniques of XAS, which are EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure). An explanation of some of the parameters used to obtain XAS data and data reduction from raw spectroscopic data is discussed. Finally, some applied examples are given that has been obtained though the use of XAS ...
TL;DR: In this paper, an in situ IR, EPR, and high resolution XANES study on the Cu+−ZSM-5.2 complexes formed at 80 K was performed.
TL;DR: In this article, the local structure of iron in three tektites has been studied by means of Fe K-edge extended X-ray absorption fine structure (EXAFS) and high-resolution Xray absorption near-edge structure (XANES) spectroscopy in order to provide quantitative data on distance and Fe coordination number.
TL;DR: In this paper, it was shown that the dyes most probably form a monolayer at the surface of anatase nanoparticles, which leads to a stronger distortion of the local environment of Ti atoms.
Abstract: Prototype solar cells made up of nanocrystalline anatase supported on a conducting glass and sensitized with two Ru2+ complexes (cis-dithiocyanatobis(2,2‘-bipyridine-4,4‘-dicarboxylate)ruthenium(II), or red dye, and (4,4‘,4‘ ‘-tricarboxy-2,2‘:6‘,2‘ ‘-terpyridine)ruthenium(II), or black dye) are characterized with out-of-plane X-ray diffraction, X-ray photoelectron spectroscopy, and Ti K-edge XAFS (XANES and EXAFS), as well as by powder X-ray diffraction of the pure dyes used for a coating of a TiO2 layer. The data indicate, within the sensitivity limits of the methods applied, that the dyes most probably form (partial coverage) a monolayer at the surface of anatase nanoparticles. Coating with the dyes leads to a stronger distortion of the local environment of Ti atoms in anatase nanoparticles.
TL;DR: Polarization-dependent near edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to determine the ordering of octadecyltrichlorosilane (OTS) molecules in self-assembled (SA) films on Si/SiOx.
Abstract: Polarization-dependent near edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to determine the ordering of octadecyltrichlorosilane (OTS) molecules in self-assembled (SA) films on Si/SiOx. Coverages of adsorbed material for different SA films were determined by integration of the NEXAFS signal due entirely to the C 1s absorption. The structures and coverages of the SA films deposited by chemisorption from solution in toluene were determined for two different deposition conditions: (1) open to the atmosphere and (2) water- and oxygen-free conditions inside a drybox. SA films of OTS deposited under ambient air conditions grew as islands on the substrate and were well-ordered as indicated by a strong polarization-dependence in the NEXAFS spectra. For depositions performed in the drybox, ordered or disordered films grew uniformly over the substrate. Ordered SA films deposited in the drybox exhibited higher average tilt angles and lower coverages of adsorbed material than SA films deposited u...
TL;DR: In this paper, Wang et al. used near-edge x-ray absorption fine structure (NEXAFS) spectroscopy at the oxygen K-edge, in conventional mode, and using the photon-stimulated desorption mode, which is surface sensitive.
Abstract: Vapor-deposited H2O ice films grown between 38 and 150 K under ultrahigh vacuum conditions have been investigated using near-edge x-ray absorption fine structure (NEXAFS) spectroscopy at the oxygen K-edge, in conventional mode—which is bulk sensitive-, and using the photon-stimulated desorption mode (PSD-NEXAFS), which is surface sensitive. By recording simultaneously those two signals, we have evidenced the differences between the surface and bulk electronic and atomic structures, for both amorphous porous ice condensed at 40 K and crystalline ice condensed at 150 K. We have also followed the bulk and surface evolutions of an amorphous ice film annealed from 38 to 147 K. A steep change in the local atomic structure of the bulk is observed, likely related to the high-density amorphous ice→low-density amorphous ice phase transition between 38 and 55 K. We have shown that the surface of crystalline ice is well ordered, but this order is different from that of the bulk. We have evidenced that the H2O–H2O int...
TL;DR: In this article, a modified sol−gel method was used to obtain nanostructured TiO2 catalysts with different crystal sizes (i.e., 3, 5, and 6 nm) but identical aggregate size and shape.
Abstract: Nanostructured TiO2 with different crystal sizes (i.e., 3, 5, and 6 nm) but identical aggregate size (i.e., 100 nm) and shape (sphere) were successfully made using a modified sol−gel method. TiO2 catalysts with crystal size of 5 nm and aggregate size of 100 nm were also prepared. This batch of catalysts has similar phase structure, surface area, band-gap energy, and degree of surface hydroxylation, and differs mainly in their crystallinity. Synchrotron XRD, XANES and EXAFS, Raman spectroscopy and transmission electron microscopy (TEM) were used to characterize the structural properties of the nanometer sized TiO2, whereas ultraviolet, X-ray photoelectron and electron paramagnetic resonance spectroscopy provided important information on the electronic properties of these nanoparticles. The catalytic performance of the nanostructured TiO2 for gas-phase photocatalytic oxidation of trichloroethylene exhibited strong dependency on both crystal size and crystallinity.
TL;DR: In this paper, a new soft X-ray (50-1500 eV) beamline has been constructed at a bending magnet station at the Photon Factory in order to perform photoemission spectroscopy (PES), x-ray absorption fine structure (XAFS), photoelectron diffraction (PED) experiments in surface chemistry.
TL;DR: The combination of quantum and statistical calculations with the XANES spectrum is found to be very fruitful to get insight into the quantitative estimation of structural properties of electrolyte solutions.
Abstract: Extended X-ray absorption fine structure (EXAFS) spectra of Cr3+ and Rh3+ in aqueous solution are analyzed and compared with computed spectra derived from structural results obtained by molecular dynamics (MD) simulation. This procedure quantifies the reliability of the EXAFS structural determination when applied to ions in solution. It provides guidelines for interpreting experimental spectra of octahedrally coordinated metal cations in aqueous solution. A set of relationships among Debye−Waller factors is proposed on the basis of MD results to reduce the number of independent fit parameters. The determination of the second hydration shell is examined. Calculated XANES spectra compare well with experimental ones. Indeed, the splitting observed on the main peak of the Rh K-edge was anticipated by the calculations. Simulated spectra from MD structures of increasing cluster size show a relationship between the second hydration shell and features of the XANES region at energies just above the edge. The combi...
TL;DR: In this paper, the authors used Co K-edge X-ray absorption spectroscopy (XAS) to investigate variations in the local structure during the first electrochemical cycle of the insertion−extraction of lithium into CoO.
Abstract: Cobalt oxide is known to exhibit a large capacity as a negative electrode in lithium-ion batteries. Here, Co K-edge X-ray absorption spectroscopy (XAS) was used to investigate variations in the local structure during the first electrochemical cycle of the insertion−extraction of lithium into CoO. The XANES and EXAFS spectra in LiyCoO (y: lithium content) varied markedly with the lithium content. The initial insertion of lithium leads to the reduction of Co2+ in the pristine CoO to the reduced metallic Co0 state. The systematic variations observed in intensities of the peaks corresponding to the 1s → 3d and 1s → 4p transitions indicate that the mole ratio of Co to CoO increases gradually with the electrochemical insertion of lithium ions. Insertion of lithium causes the local structure around the Co atoms to become asymmetric. The systematic decrease in the magnitude of the Fourier transform (FT) with increasing amount of inserted lithium is closely related to an increase in static disorder due to the pre...
TL;DR: In this article, the authors presented the case for exploiting time-resolved x-ray absorption to study structural dynamics in the liq. phase of H2O photodetachment.
Abstract: The authors present the case for exploiting time-resolved x-ray absorption to study structural dynamics in the liq. phase. With this aim in mind and considering the large differences between absorption coeffs. in the optical and the x-ray domains as well as the x-ray absorption cross sections due to unexcited species, the authors have estd. the anticipated signal-to-noise ratio (S/N) under realistic conditions with femtosecond laser pump pulses and synchrotron radiation x-ray probe pulses. As a model system, the authors examine I- photodetachment in H2O and detect the appearance of laser-generated neutral I atoms by their x-ray near-edge absorption structure (XANES) and by their extended x-ray absorption fine structure (EXAFS). While the S/N ratio critically depends on the photolysis yield, which itself is governed by the optical absorption cross section, the optimum sample concn. varies in a complex fashion as a function of pump laser intensity and optical absorption cross section. However, concns. yielding near total absorption of the pump laser deliver quite optimum S/N ratios. The calcns. presented here provide guidelines for the implementation of time-resolved x-ray absorption expts. in condensed phase chem. systems. [on SciFinder (R)]
TL;DR: In this paper, the coordination of carbon atoms in diamond-like carbon (DLC) thin films formed by Ar gas cluster ion beam (GCIB) assisted deposition using fullerene as the carbon source was investigated by measuring near-edge X-ray absorption fine structure (NEXAFS) spectra of the carbon K-edge over the excitation energy range 275-320 eV, using synchrotron radiation.
Abstract: The coordination of carbon atoms in diamond-like carbon (DLC) thin films formed by Ar gas cluster ion beam (GCIB) assisted deposition using fullerene as the carbon source was investigated by measuring near-edge X-ray absorption fine structure (NEXAFS) spectra of the carbon K-edge over the excitation energy range 275–320 eV, using synchrotron radiation. With attention to the peak corresponding to the transition of the excitation electron from a carbon 1s orbital to a π* orbital, relative sp2 contents of various DLC films were estimated. The sp2 contents of the DLC films formed by the GCIB-assisted deposition were observed to be lower than those of the DLC films formed by other methods. The hardness value measured with a nano-indentation technique was found to be strongly related to the sp2 content of the DLC film.