Showing papers on "Extended X-ray absorption fine structure published in 1978"
TL;DR: In this article, the interaction of cupric ions with γ-alumina supports was studied by physical characterization of a wide range of catalyst preparations, and the results from different techniques, including extended X-ray absorption fine structure (EXAFS), Xray absorption edge shifts, Xray diffraction, ESR, ESCA, and optical spectroscopy, were combined with prior work to develop a coherent description of the phases present and cation site distribution in the virgin and aged catalysts.
258 citations
TL;DR: An Auger variant of the x-ray-absorption fine-structure (EXAFS) technique has been successfully applied to study the adsorption site and adsorbate-substrate bond length in a single-crystal system as discussed by the authors.
Abstract: An Auger variant of the x-ray-absorption fine-structure (EXAFS) technique has been successfully applied to study the adsorption site and adsorbate-substrate bond length in a single-crystal system. The surface-EXAFS technique should have widespread applications in surface crystallographic studies.
166 citations
TL;DR: The extended X-ray absorption fine structure (EXAFS) as discussed by the authors provides structure information on the local atomic environment surrounding the absorbing atom, without requiring crystallinity of the sample, which makes feasible structure measurements in many systems which have defied previous analysis by standard techniques.
Abstract: The present article describes the basic physics and some applications of a new technique for structure determination using X-ray absorption. The extended X-ray absorption fine structure (EXAFS) on the high energy side of absorption edges contains structure information on the local atomic environment surrounding the absorbing atom. Because EXAFS supplies the local structure about each type of atom in the sample, separately, without requiring crystallinity of the sample, it makes feasible structure measurements in many systems which have defied previous analysis by standard techniques. Some examples of diverse applications of the technique are given such as: characterizing adsorbed surface atoms; studying catalysts; measuring the environment around the metal atom in metalloproteins; determining the structure of liquids, glasses and amorphous solids; and measuring solids under high pressure. The article concludes by pointing out how the intense X-ray sources recently produced by synchrotron radiatio...
120 citations
TL;DR: EXAFS spectra have been obtained of oxy and deoxy complexes of haemoglobin and of the ‘picket fence’ porphyrin, using synchrotron radiation as a source of X rays.
Abstract: EXAFS spectra have been obtained of oxy and deoxy complexes of haemoglobin and of the 'picket fence' porphyrin, using synchrotron radiation as a source of X rays. The fluorescence data were Fourier filtered to obtain distances to the first shell and corrections applied to remove contributions from the axial ligands. In this way, the iron to porphinato nitrogen distances were determined to be 1.98 +/- 0.01 A for both oxygenated complexes and 2.055 +/- 0.01 A for both deoxy forms.
114 citations
113 citations
TL;DR: In this paper, the absorption coefficients of polycrystalline CuInS2 and CuInSe2 thin films have been determined at room temperature using transmission measurements, and the effects of annealing on the absorption coefficient spectra of these chalcopyrite materials are presented.
Abstract: The absorption coefficients, α, of polycrystalline CuInS2 and CuInSe2 thin films have been determined at room temperature using transmission measurements. For each of these semiconductors, an absorption edge corresponding to the direct band‐gapl transition (1.54±0.02 eV for CuInS2 and 1.00±0.02 eV for CuInSe2) is observed in the α vs hν spectrum. In p‐type CuInS2 thin films, another edge is evident at lower energies (1.41×1.42 eV) and is attributed to transitions from a copper vacancy band to the conduction band. The effects of annealing on the absorption coefficient spectra of these chalcopyrite materials are presented. An additional absorption region, appears in the CuInSe2 spectra at higher energies (hν∠1.28 eV), and is critically dependent on the Se concentration of the films. This effect is discussed in terms of band structure, film stoichiometry and structural characteristics of the films.
111 citations
106 citations
TL;DR: In this paper, the carbon $K$ edge in graphite was measured using inelastic-electron-scattering spectroscopy and the extended x-ray absorption fine structure was in good agreement with theory for the first-neighbor atoms at a distance of 1.42 \AA{}.
Abstract: We have measured the carbon $K$ edge in graphite using inelastic-electron-scattering spectroscopy. The extended x-ray absorption fine structure is in good agreement with theory for the first-neighbor atoms at a distance of 1.42 \AA{}. The momentum dependence of the edge structure is in qualitative agreement with a simple band-structure picture. A comparison of the signal counting rates for electron-energy-loss and photoabsorption experiments shows that the energy-loss method is competitive with synchrotron radiation sources up to about 1000 eV.
100 citations
TL;DR: In this paper, extended-x-ray-absorption fine-structure spectra in the region of the Cu K$ edge are presented for Cu, CuO, ${\mathrm{Cu}}_{2}$O, CuS${O}}_{4}$\ifmmode\cdot\else\textperiodcentered\fi{}3${H}}{2}
Abstract: Extended-x-ray-absorption fine-structure spectra in the region of the $\mathrm{Cu} K$ edge are presented for Cu, CuO, ${\mathrm{Cu}}_{2}$O, CuS${\mathrm{O}}_{4}$, CuS${\mathrm{O}}_{4}$\ifmmode\cdot\else\textperiodcentered\fi{}5${\mathrm{H}}_{2}$O, Cu${(\mathrm{OH})}_{2}$, Cu(N${\mathrm{O}}_{3}$)\ifmmode\cdot\else\textperiodcentered\fi{}3${\mathrm{H}}_{2}$O, ${[\mathrm{C}\mathrm{u}{(\mathrm{N}{\mathrm{H}}_{3})}_{4}]}^{2+}$, and Cu${\mathrm{Br}}_{2}$. By the usual Fourier-analysis method, bond lengths for Cu-O, Cu-N, and Cu-Br are determined. Further, a back-transformation into real space is used which allows us to check the consistency of the evaluation for the whole energy range investigated. The advantages of this evaluation are: bond lengths can be taken from regions of high accuracy of the experimental data, the $k$ dependence of the phase shifts can be checked and this presentation gives a criterion on how to fit the reference energy necessary for the energy-momentum conversion. The bond lengths determined with this method agree to within 0.02 \AA{}A with reliable x-ray diffraction data.
91 citations
TL;DR: In this paper, the authors measured the intrinsic luminescence at 4.44 eV due to self-trapped exciton recombination in a single crystal of Ca${\mathrm{F}}_{2}$ at liquid-nitrogen temperature.
Abstract: Excitation spectra of the 4.44-eV intrinsic luminescence in a single crystal of Ca${\mathrm{F}}_{2}$ at liquid-nitrogen temperature was measured using synchrotron radiation in the x-ray region. The intrinsic luminescence at 4.44 eV is due to self-trapped exciton recombination. The intensity of the emitted uv light was measured as a function of the x-ray photon energy from below the calcium $K$ edge to 200 eV above the edge. Dips were observed in the luminescence excitation spectrum corresponding to peaks in the absorption coefficient both in the core excitation region near the edge and in the region of excitation to the continuum far above the edge. The effect is correlated with modulation of the radiative recombination probability of the core hole. The close relationship between the inverse of the luminescence yield and the extended x-ray absorption fine structure (EXAFS) after background subtraction shows that excitation spectra of uv luminescence can be used to measure EXAFS in thick single crystals and biological samples with suitable luminescence centers.
89 citations
TL;DR: In this article, Synchroton radiation has been used to obtain high resolution soft X-ray absorption spectra above the carbon K-edges in CH4, CD4 and the fluoromethanes.
TL;DR: In this paper, the extended x-ray absorption fine structure (EXAFS) above the oxygen K edge (h..nu.. approx. = 535 eV) has been investigated for an oxidized Al surface.
Abstract: The extended x-ray absorption fine structure (EXAFS) above the oxygen K edge (h..nu.. approx. = 535 eV) has been investigated for an oxidized Al surface. The spectra were obtained using monochromatized synchrotron radiation in the 500--800-eV range and detecting the secondary electron yield from the sample. Pronounced EXAFS was observed extending at least 300 eV beyond the edge. Experiments of the present kind appear to have great applicability for the study of the oxidation and catalytic activity of surfaces.
TL;DR: The agreement between the average distances in rubredoxin and the model compounds and the small spread allowable in the rubredox distances lead to the conclusion that any strain energy in the iron — sulfur bonds of Rubox is appreciably less than thermal energy.
TL;DR: The primary coordination environment of the "blue" copper ion in oxidized azurin has been elucidated by x-ray absorption spectroscopy, and there is some evidence that the copper coordination sphere may be completed by a second sulfur.
Abstract: The primary coordination environment of the “blue” copper ion in oxidized azurin has been elucidated by x-ray absorption spectroscopy. The most striking feature is the unambiguous presence of a very short copper-sulfur distance at 2.10 ± 0.02 A. Nitrogen ligands, presumed to be from imidazoles, are found at 1.97 A. There is some evidence that the copper coordination sphere may be completed by a second sulfur, the distance of which is determined with much less certainty.
TL;DR: In this article, small angle inelastic scattering of 2.5 keV electrons was used to study the inner shell excitation of CH4, CH3Cl, CH2Cl2, CHCl3, CCl4 and C2H5Cl in the regions of carbon 1s, chlorine 2p and chlorine 2s excitation.
PARC1
TL;DR: In this article, the authors discuss the theoretical background and practical aspects of EXAFS data analysis and apply them to the analysis of arsenic dopants in amorphous silicon and of PdGe metallic glass.
Abstract: The availability of intense sources of continuous radiation in the X-ray region has stimulated the development of a technique for structure determination which is particularly suited to studies of local environment in complex systems. The absorption cross section for the photoexcitation of an electron from a deep core state to a continuum state exhibits oscillations as a function of photon energy known as the extended X-ray absorption fine structure, or EXAFS. These oscillations result from the interference between the outgoing photoelectron wavefunction and that portion of it scattered back from neighboring atoms, and therefore contain considerable information about the local environment of the excited atom species. Analysis of the EXAFS can yield not only the distance but also the type and number of the nearest neighbors of the excited atom. The purpose of this paper is to discuss briefly the theoretical background and the practical aspects of EXAFS data analysis. The discussion is then illustrated through application of these techniques to EXAFS studies of arsenic dopants in amorphous silicon and of PdGe metallic glass.
TL;DR: In this article, the authors show a local ordering of the Cu and Br ions in planar structure which spreads as the concentration is increased up to saturation, which is a direct confirmation of the local-ordering model proposed recently on the basis of Raman and viscosity measurements.
Abstract: EXAFS (extended x-ray-absorption fine structure) spectra of Cu${\mathrm{Br}}_{2}$ aqueous solutions at various concentrations have been analyzed both for Br and Cu $K$ edges. They show a local ordering of the Cu and Br ions in planar structure which spreads as the concentration is increased up to saturation. Our data give a direct confirmation of the local-ordering model proposed recently on the basis of Raman and viscosity measurements.
TL;DR: In this article, the x-ray absorption edges in solids show extended fine structure up to 30-60 Hartrees (1 or 2 keV) above the edge which is known to be caused by electron scattering from other atoms surrounding the absorbing atom.
Abstract: X-ray absorption edges in solids show extended fine structure up to 30-60 Hartrees (1 or 2 keV) above the edge which is known to be caused by electron scattering from other atoms surrounding the absorbing atom. In addition other structure is sometimes observed, of a slower period, especially nearer to the edge, which are shown to be caused by scattering in the periphery of the absorbing atom. The new structure is closely related to the derivative of the p-phase shift in the case of K-shell excitation, and improved values of the phase shift can be extracted from experiment.
TL;DR: In this article, the authors reported initial measurements on the extended x-ray absorption fine structure (EXAFS) of the Fe $K$ edge in Fe$S$ to 64 kbar and Fe$F$S 2 to 21 kbar.
Abstract: Initial measurements are reported on the extended x-ray-absorption fine structure (EXAFS) of the Fe $K$ edge in Fe${\mathrm{S}}_{2}$ to 64 kbar and Fe${\mathrm{F}}_{2}$ to 21 kbar. With this new technique the Fe-Fe spacings are directly observed to vary in accordance with high-pressure x-ray diffraction measurements of the corresponding lattice parameters. In contrast, the Fe-S spacing in pyrite is found to be much less compressible. Pressure reduction of the mean-square deviations in the iron-ligand bond lengths are also given.
TL;DR: In this article, the authors used Extended x-ray absorption fine structure (EXAFS) spectroscopy to test the binding sites of cis-diammineplatinum and trans-[Pt(NH3)iC!i] bound to calf thymus DNA.
Abstract: The complex cis-dichlorodiammineplatinum(II) (DDP) is an active antitumor drug while the trans-DDP isomer is ineffective, a result that may reflect differences in their ability to bind DNA.[1-5] While various chemical and physical techniques have been used to explore the interactions of these platinum compounds with DNA, there appears to be no direct structural information about the resulting platinum-DNA complex. Recent crystallographic study[5c] of the blue compound formed between cis-diammineplatinum and a-pyridone (1) suggested[5b] that thymine (2, R = CH3) and guanine (3) bases in DNA might bridge two cis-diammineplatinum units using the deprotonated amide nitrogen and the exocyclic oxygen as donor atoms. The resulting complex would have a short Pt-Pt distance, 2.5-3.2 A, depending upon the platinum oxidation state. To test this possibility and to provide information about the binding sites ofDDP, samples of cis- and trans-[Pt(NH3)iC!i] bound to calf thymus DNA, 4 and 5, respectively, were prepared and studied by extended x-ray absorption fine structure (EXAFS) spectroscopy.
TL;DR: Pulsed-dye-laser excitation has been used to investigate the optical absorption and emission spectra of Li atoms trapped in Ar, Kr, and Xe matrices at 10 K as mentioned in this paper.
Abstract: Pulsed‐dye‐laser excitation has been used to investigate the optical absorption and emission spectra of Li atoms trapped in Ar, Kr, and Xe matrices at 10 °K. Attempts to stabilize Li atoms in a Ne matrix at 2 °K were unsuccessful. Results for all three rare gases were qualitatively the same. White light absorption scans showed a single absorption with three peaks centered near the free‐atom 2s→2p transition wavelength. The intensity of fluorescence produced by dye‐laser excitation within this absorption band was measured as a function of emission wavelength. Excitation of the longest‐ and shortest‐wavelength absorption peaks produced identical emission profiles, but no distinct fluorescence signal was detected when the laser was tuned to the central absorption peaks, indicating that the apparent absorption triplet is actually the superposition of a singlet and a doublet absorption originating from two different trapping sites. No additional absorption bands were detected.
TL;DR: In this article, a rate was derived for n-photon absorption which includes all atomic and laser linewidths and experimentally checked the laser linwidth dependence for two-poton absorption.
Abstract: A rate is derived for n-photon absorption which includes all atomic and laser linewidths and experimentally check the laser linewidth dependence for two-photon absorption.
TL;DR: In this paper, the gross absorption structures in the VUV region were analyzed by comparison of the experimental results in photoelectron spectroscopy with the absorption spectra of the sulphur L2,3.
Abstract: Absorption and ionisation efficiencies for SF6 have been measured in the VUV region. An analysis of the gross absorption structures is given by comparison of the experimental results in photoelectron spectroscopy with the absorption spectra of the sulphur L2,3. All the absorption structures in the VUV region observed are interpreted consistently with the two-well potential scheme. The vibrational progressions in the range 550-670 AA are also assigned to the Rydberg series caused by the transitions, 4t1u-nsa1g (n>or=3).
TL;DR: In this article, the authors compared the recombination light intensity produced in GaAs by a 1.06 μm pulse inducing two-photon absorption, with the intensity produced by a 0.53μm pulse.
Abstract: Comparing the recombination light intensity produced in GaAs by a 1.06 μm pulse inducing two-photon absorption, with the intensity produced by a 0.53 μm pulse, we obtain directly the two-photon absorption cross-section. This method can be generalized to other materials.
TL;DR: In this paper, the radial structure function, the envelope function, and the scattering phase of a single Cu shell have been calculated from the yield spectrum, which is similar to those extracted from the absorption coefficient.
Abstract: The variation with the photon energy of the photoelectron yield of Cu has been measured near the K edge. The fine structure of the yield agrees with the fine structure of absorption spectra (EXAFS). The radial structure function, the envelope function, and the scattering phase of a single Cu shell have been calculated from the yield spectrum. The results are similar to those extracted from the absorption coefficient. The yield increases with decreasing glancing angle of the incident photons. A variation of the height of the Cu edge and the amplitude of the EXAFS modulation with this angle is observed. This is explained by the escape mechanism of the electrons.
TL;DR: In this paper, the probability of electron scattering from atomic core states as a function of electron energy, can be extracted from secondary electron yields by differentiation, and fine structure variations above the thresholds for excitation of the vanadium 2p and 2s states are found to extend for several hundred electron volts.
TL;DR: Extended X-ray absorption fine structure (EXAFS) experiments indicate that the nearest-neighbour distribution centred about the As atom of amorphous GaAs peaks at a distance of 0.04 AA greater than that of the crystalline form, while the nearestneighbor distribution centered about Ga is the same as that of a crystal to within 0.015 AA as mentioned in this paper.
Abstract: Extended X-ray absorption fine structure (EXAFS) experiments indicate that the nearest-neighbour distribution centred about the As atom of amorphous GaAs peaks at a distance of 0.04 AA greater than that of the crystalline form, while the nearest-neighbour distribution centred about Ga is the same as that of the crystal to within 0.015 AA. The differences in the two spacings indicates that the chemical disorder must be present in amorphous GaAs.