Showing papers on "Extended X-ray absorption fine structure published in 1989"
TL;DR: In this article, the utility of sulfur K-edge X-ray absorption spectroscopy for the determination and quantification of sulfur forms in petroleum asphaltenes has been investigated and the results represent the first demonstration that nonvolatile sulfur forms can be distinguished and approximately quantified by direct measurement.
Abstract: The utility of sulfur K-edge X-ray absorption spectroscopy for the determination and quantification of sulfur forms in petroleum asphaltenes has been investigated. Both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra were obtained for a selected group of model compounds and for several petroleum asphaltene samples. For the model compounds the sulfur XANES was found to vary widely from compound to compound and to provide a fingerprint for the form of sulfur involved. The use of third derivatives of the spectra enabled discrimination of mixtures of sulfidic and thiophenic model compounds and allowed approximate quantification of the amount of each component in the mixtures and in the asphaltene samples. These results represent the first demonstration that nonvolatile sulfur forms can be distinguished and approximately quantified by direct measurement.
244 citations
TL;DR: X-ray absorption spectroscopy (XAS) was used to follow the evolution of local structural environments around ferric ions during the formation of ferric hydrous oxide gels from 1 M chloride and 0.1 M nitrate solutions as discussed by the authors.
193 citations
TL;DR: In this paper, an absorption spectrum containing both the XANES and the EXAFS region can be recorded in several seconds if x-ray monochromators at synchrotron beamlines are scanned continuously.
Abstract: An absorption spectrum containing both the XANES and the EXAFS region can be recorded in several seconds if x‐ray monochromators at synchrotron beamlines are scanned continuously. The experimental setups are described in detail. The accuracy of the method up to photon energies of 19 keV is demonstrated. Due to its advantages, the proposed approach may be used as an alternative to the energy dispersive EXAFS method, especially in the case of XANES spectroscopy.
168 citations
120 citations
105 citations
TL;DR: In this article, small ensembles of CdSe have been synthesized within the cage system of zeolite Y via ion exchange with Cd(II) and subsequent treatment with H{sub 2}Se.
Abstract: Small ensembles of CdSe have been synthesized within the cage system of zeolite Y via ion exchange with Cd(II) and subsequent treatment with H{sub 2}Se. Cluster size and geometrical arrangements could be determined by comprehensive analysis of Cd- and Se-edge EXAFS data as well as synchrotron X-ray powder diffraction and model calculations. The uptake of Se by the zeolite and bond formation to cadmium ions with a bond length of 2.60 {angstrom} are clearly evident from EXAFS data of both absorption edges. The CdSe molecular clusters are stabilized at ambient conditions through strong interactions with the zeolite host. Rietveld analysis and EXAFS results indicate the presence of 70% of the cadmium ions at SI' and 30% at SIII. Se,O-bridged cadmium dimers and Cd{sub 4}O{sub 4} cubes are formed in the sodalite unit. Cadmium ions present in 12-ring windows are coordinated to one Se and additional oxygen atoms. Small amounts of Se helical chains and CdSe clusters are also detected.
99 citations
TL;DR: In this paper, the Jahn-Teller distortion of the Cu2+ (H2O)6 cluster in aqueous solution has been studied by X-ray near edge structure spectroscopy and it was shown that a conventional EXAFS analysis, even supplied with state-of-the-art theoretical improvements, fails to discriminate between distorted or undistorted clusters in solution.
83 citations
TL;DR: It is experimentally confirmed for the first time that x-ray Raman spectroscopy by using hard x rays can supply the same information as the soft-x-rayEXAFS, and can thus be a substitute for EXAFS to determine the local structure around low-atomic-number elements whose EXAFs study is plagued with inherent experimental difficulties.
Abstract: We have recorded x-ray Raman-scattering spectra from graphite and diamond with high resolution and good signal-to-noise (S/N) ratio by excitation with hard x rays from synchrotron radiation. The scattering spectra show characteristics predicted by the theory. The observed scattering spectrum for graphite was not exactly the same as the absorption spectrum, possibly because of polarization effects in the anisotropic materials. In the case of diamond powder, however, oscillations identical with those found in the extended x-ray-absorption fine structure (EXAFS) spectrum were observed, and from an analysis employing the formula used for EXAFS, interatomic distances were obtained. Thus, it is experimentally confirmed for the first time that x-ray Raman spectroscopy by using hard x rays can supply the same information as the soft-x-ray EXAFS. X-ray Raman spectroscopy can thus be a substitute for EXAFS to determine the local structure around low-atomic-number elements whose EXAFS study is plagued with inherent experimental difficulties.
73 citations
TL;DR: The extended x-ray-absorption fine structure (EXAFS) and near-edge structure (XANES) at the Pd /ital K/ edge were used to observe the interaction of hydrogen with palladium clusters, 5 nm in average size, supported on alumina.
Abstract: The extended x-ray-absorption fine structure (EXAFS) and x-ray-absorption near-edge structure (XANES) at the Pd K edge were used to observe the interaction of hydrogen with palladium clusters, 5 nm in average size, supported on alumina A sample was reduced in flowing dihydrogen at 573 K and atmospheric pressure This sample was then cooled to room temperature (RT) in dihydrogen, allowing for the formation of \ensuremath{\beta}-phase palladium hydride Another sample was reduced in the same way, but then evacuated at 573 K to prevent formation of the hydride This sample was cooled to RT in vacuo and contacted with helium at atmospheric pressure Analysis of the Pd EXAFS recorded at RT showed a 37% increase in the Pd-Pd distance and greater disorder for the hydride compared to the sample free of hydride The XANES results were consistent with a narrowing of the l=1 band features for the hydride sample due to the increased Pd-Pd distance In addition, the line shape of the edge for the hydride may result from hydrogen lowering the number of unoccupied p-like states near the Fermi level of Pd The observed lattice expansion and modified electronic structure have been reported for bulk palladium hydride
71 citations
TL;DR: In this article, photo-acoustic spectroscopy, ESR and EXAFS measurements have been carried out on the Se chains isolated in the channels of mordenite crystal with 6.7 A diameter.
Abstract: Photoacoustic spectroscopy, ESR and EXAFS measurements have been carried out on the Se chains isolated in the channels of mordenite crystal with 6.7 A diameter. The optical gap is estimated to be 2.3 eV at room temperature, which is much larger than that of trigonal Se. At low temperatures, illumination with the light having energy near or above the optical gap induces new absorption bands at 1.85 and 2.25 eV, which are associated with paramagnetic defects. Higher energy light (>2.9 eV) shifts the absorption edge to lower energy. The fluctuations in the covalent bond length increase with illumination, though the helical chain structure is preserved. These changes vanish by annealing at room temperature. The phenomena are reversible in the illumination and annealing cycle. The photo-induced absorption and the edge shift are reduced when the induced bands are excited optically.
65 citations
TL;DR: In this paper, the structure of methyl mercaptide (CH3S-) on Cu(111) has been investigated by surface EXAFS above the S K-edge and by normal incidence standing X-ray wavefield absorption, monitoring the same S Kshell absorption around the (111) Bragg reflection.
TL;DR: An energy-temperature curve is proposed to assist in selection of candidate absorption lines and two techniques, the effective absorption path length method and the direct curve-fit method, are proposed to extract absolute concentrations from absorption data obtained in the presence of boundary layers.
Abstract: The effect of thermal and concentration boundary layers on experimental data must be well understood for a successful diagnostic measurement of quasi-uniform high-temperature gases using line-of-sight absorption spectroscopy. In this paper, an energy–temperature curve is proposed to assist in selection of candidate absorption lines. Two techniques, the effective absorption path length method and the direct curve–fit method, are proposed to extract absolute concentrations from absorption data obtained in the presence of boundary layers.
TL;DR: The optical absorption coefficient for subgap electronic transitions in crystalline and disordered semiconductors is calculated by first-principles means with use of a variational principle based on the Feynman path-integral representation of the transition amplitude with excellent agreement with experimental data.
Abstract: The optical absorption coefficient for subgap electronic transitions in crystalline and disordered semiconductors is calculated by first-principles means with use of a variational principle based on the Feynman path-integral representation of the transition amplitude This incorporates the synergetic interplay of static disorder and the nonadiabatic quantum dynamics of the coupled electron-phonon system Over photon-energy ranges of experimental interest, this method predicts accurate linear exponential Urbach behavior of the absorption coefficient At finite temperatures the nonlinear electron-phonon interaction gives rise to multiple phonon emission and absorption sidebands which accompany the optically induced electronic transition These sidebands dominate the absorption in the Urbach regime and account for the temperature dependence of the Urbach slope and energy gap The physical picture which emerges is that the phonons absorbed from the heat bath are then reemitted into a dynamical polaronlike potential well which localizes the electron At zero temperature we recover the usual polaron theory At high temperatures the calculated tail is qualitatively similar to that of a static Gaussian random potential This leads to a linear relationship between the Urbach slope and the downshift of the extrapolated continuum band edge as well as a temperature-independent Urbach focus At very low temperatures, deviations from these rules are predicted arising from the true quantum dynamics of the lattice Excellent agreement is found with experimental data on c-Si, a-Si:H, a-${\mathrm{As}}_{2}$${\mathrm{Se}}_{3}$, and a-${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ Results are compared with a simple physical argument based on the most-probable--potential-well method
Patent•
21 Dec 1989TL;DR: In this article, a medical treatment laser is disclosed that minimizes absorption of laser energy along the beam path by using a lasing medium having a principal emission at a wavelength shifted from the absorption wavelength.
Abstract: A medical treatment laser is disclosed that minimizes absorption of laser energy along the beam path by using a lasing medium having a principal emission at a wavelength shifted from the absorption wavelength. In the preferred embodiment, a CO 2 laser filled with the 13 C 16 O 2 isotope is used. The 13 C 16 O 2 isotope generates a laser beam having a principal emission wavelength near 11.2 microns. The absorption of this wavelength in the conventional CO 2 purge and insufflation gases is quite small compared to the absorption of the 10.59 micron wavelength emitted by the standard CO 2 isotope. The difference in absorption allows the power generated by the laser to be maximally transmitted to the medical treatment site. In addition, the 11.2 micron line has a greater coefficient of absorption in human tissue, thereby enhancing surgery.
TL;DR: In this article, the structure of the molybdenum site of xanthine oxidase in the complexes with alloxanthine, violapterin, and 6-pteridylaldehyde has been investigated by using x-ray absorption spectroscopy.
Abstract: The structure of the molybdenum site of xanthine oxidase in the complexes with alloxanthine, violapterin, and 6-pteridylaldehyde has been investigated by using x-ray absorption spectroscopy. The strongest component in the EXAFS spectrum is assigned to Mo-S bonds at 2.38 {plus minus} 0.03, 2.40 {plus minus} 0.03, and 2.46 {plus minus} 0.03 {angstrom}, respectively. In all cases, a second EXAFS component was identified as corresponding to a terminal oxo group with a bond length of 1.66-1.71 {angstrom}. A terminal sulfur ligand, with a Mo=S bond length of 2.20 {plus minus} 0.03 {angstrom}, was observed for the oxidized 6-pteridylaldehyde complex. However, the presence of a short Mo=S bond ({le} 2.30 {angstrom}) was ruled out for the alloxanthine and violapterin complexes. The EXAFS results are compared with previous proposals for the alloxanthine-xanthine oxidase complex. 27 refs., 4 figs., 1 tab.
TL;DR: In this article, the application of X-ray absorption spectroscopy (XAS) to the study of diffusion properties of oxide glasses and glass surfaces is considered. And the importance of combining XAS with diffusion measurements and structural modelling is stressed if the interdependence of structure and ionic transport is to be properly elucidated.
Abstract: The application of X-ray absorption spectroscopy (XAS) to the study of diffusion properties of oxide glasses and glass surfaces is considered. Mixed alkali silicates, the chemical resistance of iron-lead-phosphate glasses and the surface structure of uranium in leached borosilicate glasses are discussed. Results are interpreted using the modified random network (MRN) model. The importance of combining XAS with diffusion measurements and structural modelling is stressed if the interdependence of structure and ionic transport is to be properly elucidated.
TL;DR: In this paper, the spin-dependent absorption coefficient of spin-polarized photons of energies between 10.8 and 13.8 keV at the edges of Os, Ir, Pt, and Au impurities (3 at.%) in iron.
Abstract: Large spin-dependent absorption effects have been observed with circularly polarized photons of energies between 10.8 keV and 13.8 keV at theL
2,3-edges of Os, Ir, Pt, and Au impurities (3 at.%) in iron. The largest value of the spin-dependent absorption coefficient (µ
c
/µ
o
∼+0.22) is found at the PtL
2-edge. From the energy dependence of the spin-dependent absorption at theL
2- andL
3-edges the spin-density profiles of thed
3/2-andd
5/2-projected states populated in the absorption process are derived. Thed
5/2-spin densities deduced from theL
3 spin-dependent absorption spectra agree well with spin-polarized band-structure calculations for the ferromagnetic ground state. A comparison of thed
3/2- andd
5/2-spin densities shows a strong contribution of the spin-orbit effects to the exchange splitting in Os, whereas only small spin-orbit effects are indicated for Ir, Pt and Au impurities.
TL;DR: A detailed discussion about the origin of all the different features in the experimental XAS spectra and a method to extract small contributions in the EXAFS part of the spectrum is presented.
Abstract: The local structure around the vanadium site in the oriented V{sub 2}O{sub 5}{center dot}1.6 H{sub 2}O dehydrated xerogel phase is investigated by polarized x-ray-absorption spectroscopy (XAS). A large dychroism is found both in the extended x-ray-absorption fine structure (EXAFS) and in x-ray-absorption near-edge structure (XANES). A joint analysis of EXAFS and XANES data is reported. EXAFS analysis has been performed using a spherical-wave propagator and XANES analysis by full multiple-scattering calculation. A detailed discussion about the origin of all the different features in the experimental XAS spectra and a method to extract small contributions in the EXAFS part of the spectrum is presented. Moreover, the local structure around the vanadium atom in the V{sub 2}O{sub 5} hydrogel phase is derived.
TL;DR: For fused silica a two-photon absorption mechanism is found, while for CaF, LiF, and MgF(2) three-ph photon absorption and absorption due to color-center formation are found as dominant absorption mechanisms.
Abstract: Transmission of fused silica, CaF2, LiF, and MgF2 is measured using 450-fsec, 248-nm pulses in the range 10–120 GW/cm2. Different loss mechanisms such as scattering of transmitted radiation, color-center formation, and multiphoton absorption were studied separately. For fused silica a two-photon absorption mechanism is found, while for CaF2, LiF, and MgF2 three-photon absorption and absorption due to color-center formation are found as dominant absorption mechanisms.
TL;DR: In this paper, the local and average structures of YBa 2 Cu 3 O 7−δ doped with Zn were studied by the combined use of extended X-ray absorption fine structure (EXAFS) analysis and Rietveld refinement of neutron powder diffraction data.
Abstract: The local and average structures of YBa 2 Cu 3 O 7−δ doped with Zn were studied by the combined use of extended X-ray absorption fine structure (EXAFS) analysis and Rietveld refinement of neutron powder diffraction data. X-ray absorption measurements at the Zn K-edge indicate that the Zn atom has four short (2.02 A) and one long (2.25 A) Zn-O bonds. The chemical environments of the Cu and Y atoms agree well with the structure determined by neutron diffraction. The mechanism of T c of depression accompanying Zn doping is discussed.
TL;DR: In this article, a detailed analysis of synchrotron x-ray absorption data of the Pb L{sub III}-edge showed that intrazeolite PbO(sub 2)(O{sub z} = zeolite oxygen) species in Y react with H{sub 2}S to form monomolecular S{sub 1}Pb(I{sub n})-sub 3} species that are still anchored to the Zeolite framework.
Abstract: Molecular-size PbS species have been stabilized in the open-pore structure of zeolite Y and mordenite via ion exchange with Pb(II) and subsequent treatment with H{sub 2}S at 295 K. Detailed analysis of synchrotron x-ray absorption data of the Pb L{sub III}-edge shows that intrazeolite PbO{sub 2}(O{sub z} = zeolite oxygen) species in zeolite Y react with H{sub 2}S to form monomolecular S{sub 2}Pb(I{sub z}){sub 3} species that are still anchored to the zeolite framework. The intrazeolite PbS phase appears to be more ordered at high loading levels of lead in zeolite Y than at low loading levels. The coordination of Pb(II) and the structure of PbS in the mordenite host is less ordered but basically very similar to that of the monomolecular species in Y. Optical absorption data for these samples agree very well with the structural EXAFS results. Larger PbS clusters have been stabilized in 85% ethylene-15% methacrylic acid copolymer films by a similar preparation procedure. EXAFS data indicate that the reaction forms PbS clusters with several Pb coordination shells and that the conversion of PbS is a function of Pb(II) loading levels. 23 refs., 9 figs., 3 tabs.
TL;DR: The extended x-ray-absorption fine-structure (EXAFS) measurements confirm previous diffraction studies of the structure and were also used to determine the EXAFS Debye-Waller factor for a number of Bi bonds.
Abstract: Temperature-dependent x-ray-absorption measurements have been made on the Bi ${L}_{3}$ edge in (${\mathrm{Ba}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{K}}_{\mathrm{x}}$)${\mathrm{BiO}}_{3}$ with x=0 and 0.4. In the near-edge spectra there is clear evidence for Bi(6s) holes that depend on doping, but there does not seem to be a significant amount of Bi disproportionation into the 5+ and 3+ valencies in the undoped material. The extended x-ray-absorption fine-structure (EXAFS) measurements confirm previous diffraction studies of the structure and were also used to determine the EXAFS Debye-Waller factor for a number of Bi bonds. For x=0 the Debye-Waller factor differs strongly for the two types of Bi-O bonds, while for x=0.4 there is significant increase in the temperature-independent contribution. All of the temperature data could be fit well with an Einstein model, except for the Bi-O bond in a superconducting sample that showed a significant deviation from the expected behavior. These results, along with other considerations, are best explained by associating the charge-density ordering in the undoped material with holes on the O lattice and a tendency in the cubic superconducting sample towards the same type of charge-density-driven distortions.
TL;DR: In this paper, high pressure properties of krypton were investigated by energy-dispersive extended x-ray absorption fine-structure spectroscopy in a diamond anvil cell at room temperature.
Abstract: High-pressure properties of krypton were investigated by energy-dispersive extended x-ray absorption fine-structure spectroscopy in a diamond anvil cell at room temperature. The equation of state agrees very well with x-ray diffraction data. The pressure dependence of the Debye-Waller factor was determined and compared with calculations using pair potentials. The analysis of the x-ray absorption near-edge structure part of the spectrum shows the possibility of measuring the pressure in bubbles of krypton implanted in metallic matrices.
TL;DR: A versatile instrument for glancingangle x-ray absorption spectroscopy (XAS) and xray reflectivity in routine use on the Daresbury Synchrotron Radiation Source is described in this paper.
Abstract: A versatile instrument for glancing‐angle x‐ray absorption spectroscopy (XAS) and x‐ray reflectivity in routine use on the Daresbury Synchrotron Radiation Source is described This facility can be used for XAS measurements in both reflectivity and fluorescence modes as well as for qualitative studies of angular dependent x‐ray reflectivity Reflectivity and XAS data obtained with this instrument on the oxidized surfaces of Cu thin films are presented
TL;DR: In this article, the water adsorptivity of activated carbon fibres (ACF) was investigated using the Dubinin-Serpinsky equation and the number of polar sites on the surface was estimated and compared with the data from an analysis of the evolved gas.
Abstract: The Fe K-edge X-ray absorbtion near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) and the water adsorptivity of iron oxide-dispersed activated carbon fibres (ACF) have been investigated. Also, Fe K-edge XANES and EXAFS of various kinds of powdered iron oxides have been measured in order to characterize the species disperesed on the ACF. The XANES and EXAFS indicated that α-FeOOH-like ultrafine particles transform into α-Fe2O3-like particles on the ACF through heating in vacuo. The adsorption isotherms of water on the α-FeOOH-dispersed ACF were of type V. The water adsorption isotherms were analysed by the Dubinin–Serpinsky equation; the number of polar sites on the surface was estimated and compared with the data from an analysis of the evolved gas. The relationship between the water adsorptivity and the states of the iron oxides on the ACF is discussed. A comparison of nitrogen and water adsorption shows that the layer of water adsorbed on iron oxides dispersed on the ACF has a more sparse structure than normal water, and that the iron oxide-dispersed and preoxidized ACF samples exhibit an excess of water adsorptivity owing to both molecular-sieve effects and surface fractal structure.
TL;DR: The amplitude of Fe-Fe backscattering in the EXAFS spectrum indicates that FX may be a [4Fe-4S] cluster and is not a [2Fe-2S) cluster or clusters.
Abstract: We present iron extended X-ray absorption fine structure (EXAFS) spectra of a photosystem I core preparation containing FX, the very low potential iron-sulfur cluster in photosystem I. The preparation lacks FA and FB. The amplitude of Fe-Fe backscattering in the EXAFS spectrum indicates that FX may be a [4Fe-4S] cluster and is not a [2Fe-2S] cluster or clusters.
TL;DR: In this article, the structure and properties of alkali niobosilicate glasses and their interrelationship were discussed on the basis of extended X-ray absorption fine structure (EXAFS) results, Raman spectra and glass properties.
Abstract: On the basis of extended X-ray absorption fine structure (EXAFS) results, Raman spectra and glass properties, this paper discusses the structure and properties of alkali niobosilicate glasses and their interrelationship. The experimental results indicate that these glasses have non-linear properties with increasing Nb2O5 concentration. The Raman spectra show that the peak due to the NbO stretching vibration at 650 cm−1 is strengthened, broadened and shifted to higher frequency as the Nb2O5 content is increased. At the same time, with the introduction of Nb2O5 the peaks due to the SiOSi asymmetric stretching vibration (1100 cm−1) and the SiO symmetric stretching vibration (560 cm−1) for the [SiO4] tetrahedra are gradually weakened. The characteristic peak due to the SiO bond disappears and a new peak (720 cm−1) emerges when the Nb2O5 concentration is 10 mol%.
TL;DR: In this paper, the possibility of direct selective surface activation by photodeposition of autocatalytic Cu particles on photosensitiveTiO2 substrates in an alkaline electroless copper solution has been investigated.
Abstract: The possibility of direct selective surface activation by photodeposition of autocatalytic Cu particles on photosensitiveTiO2 substrates in an alkaline electroless copper solution has been investigated. The nucleation and growth of particleswere characterized by transmission electron microscopy (TEM). Ex situ high resolution TEM and in situ extendedx-ray absorption fine structure (EXAFS) spectroscopy were used to determine the oxidation state of photodeposited particleson thin polycrystalline TiO2 films and suspended TiO2 powders, respectively. It is shown that in the initial stages ofphotodeposition small (
PARC1
TL;DR: In this paper, the first neighbor cation-anion distance remains closer to that in the pure binary compound than to that of the average or virtual crystal distance, determined from the lattice constant, despite a large difference between the two.