Showing papers on "Extended X-ray absorption fine structure published in 1981"
TL;DR: In this paper, the authors discuss the theory and experiments dealing with the pulsed optoacoustic effect (i.e., generation of a transient acoustic wave by absorption of an optical pulse) in condensed matter.
Abstract: The authors discuss the theory and experiments dealing with the pulsed optoacoustic effect (i.e., generation of a transient acoustic wave by absorption of an optical pulse) in condensed matter. Their primary interest lies in the measurement of small absorption coefficients (\ensuremath{\ll}${10}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$). At present an experimental capability of measuring absorption coefficients as small as ${10}^{\ensuremath{-}6}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ has been demonstrated, and further improvement is foreseen. The pulsed optoacoustic absorption measurement technique has been applied to the following linear spectroscopic studies: (1) precise measurements of the optical absorption spectra of ${\mathrm{H}}_{2}$O and ${\mathrm{D}}_{2}$O; (b) accurate determination of absorption strengths and profiles of high harmonics ($n=6, 7, \mathrm{and} 8$) of vibrational modes in transparent organic liquids (e.g., benzene); (c) quantitative absorption spectra of thin (\ensuremath{\sim} 1-10 \ensuremath{\mu}m) liquid films; and (d) quantitative absorption spectra of solids and finely powdered crystals. The usefulness of the pulsed optoacoustic technique to nonlinear spectroscopy has been demonstrated in the following studies: (a) quantitative two-photon absorption spectroscopy of the weak two-photon ($^{1}B_{2\ensuremath{\mu}}\ensuremath{\leftarrow}^{1}A_{1g}$) transition in benzene; and (b) optoacoustic Raman-gain spectra for a variety of liquids where an ability to measure Raman gains as small as ${10}^{\ensuremath{-}5}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ has been demonstrated. In addition to reviewing the above studies the authors discuss future possible applications and compare the pulsed optoacoustic spectroscopy technique with other optoacoustic absorption measurement techniques.
568 citations
TL;DR: In this article, a series of copper foils of varying thicknesses were measured to determine the most accurate values of EXAFS amplitude for copper metal which agree well with theory as corrected for the many-body overlap effect.
Abstract: The thickness effect, which is caused by inevitable leakage radiation accompanying the desired radiation, can cause significant decreases of extended-x-ray-absorption-fine-structure (EXAFS) amplitude when the sample is thick enough. The effect is illustrated by measurements of the $K$-edge EXAFS on a series of copper foils of varying thicknesses. Significant distortions in EXAFS amplitudes occur when $\ensuremath{\Delta}{\ensuremath{\mu}}_{0}x\ensuremath{\ge}1.5$, where $\ensuremath{\Delta}{\ensuremath{\mu}}_{0}$ is the $K$-edge step in the absorption coefficient and $x$ is the sample thickness. Therefore, the optimum total sample thickness of ${\ensuremath{\mu}}_{T}x=2.6$ as determined by statistical considerations will introduce errors in EXAFS amplitudes in concentrated samples due to the thickness effect. The measurements presented here determine the most accurate values of EXAFS amplitude for copper metal which agree well with theory as corrected for the many-body overlap effect.
213 citations
206 citations
TL;DR: This chapter is concerned with polarized absorption and linear dichroism spectroscopy of hemoglobin, techniques used to study the optical properties of oriented systems.
Abstract: Publisher Summary This chapter is concerned with polarized absorption and linear dichroism spectroscopy of hemoglobin. Polarized absorption and linear dichroism are techniques that are used to study the optical properties of oriented systems. Unlike solutions, where light polarized in any direction is absorbed equally because the molecules are randomly oriented, the absorption of plane-polarized light by oriented molecules is dependent on the polarization direction of the incident light beam. Anisotropic absorption occurs because molecules fixed in space exhibit maximum absorption when the electric vector of the light is parallel to well-defined directions in the molecule. A polarized absorption experiment in which the spectra are measured in each of three orthogonal directions on a sample of known molecular orientation—such as a crystal of known structure—yields both the complete spectrum and the molecular direction of the transition moment for each absorption band. If, on the other hand, the transition moment directions are already established, the polarized absorption experiment along three orthogonal axes yields the molecular orientation. In a linear dichroism experiment, the difference between the optical densities in two directions is measured directly.
183 citations
127 citations
113 citations
TL;DR: Spectra for the two metals have been analysed using the new multiple scattering formalism and unlike a conventional band structure approach it does not require structural periodicity but works from the local arrangement of atoms.
Abstract: The measurement of X-ray absorption fine structure of metals— both in the extended region (EXAFS) as well as in the near edge region (XANES)—has been widely discussed (see refs 1–6 for Cu and refs 7–9 for Mn). The recent availability of intense X-ray fluxes from storage rings has usually been exploited for EXAFS leaving the XANES often with poorer resolution than earlier work performed on conventional sources (for example, compare the near edge structure for copper in ref. 1 with refs 3 or 6). In addition, whilst the theory and analysis of EXAFS is relatively well-established2,10, a theory for the strong scattering regime near to the absorption edge has only recently been developed11. We report here the first high resolution XANES spectra for Cu and Mn which were performed at the SRS storage ring at Daresbury. Although both metals have close-packed structures consisting of atoms of similar size their local atomic structure is different in detail. Significant differences are found in their respective XANES reflecting the senstivity of this region of the X-ray absorption fine structure to the local atomic structure. Spectra for the two metals have been analysed using the new multiple scattering formalism. This is a real space calculation and unlike a conventional band structure approach it does not require structural periodicity but works from the local arrangement of atoms.
103 citations
TL;DR: In this paper, the diffuse X-ray scattering has been measured from a single crystal of Al-17 at% Cu, aged to contain GP I zones, which are a mixture of single (001) planes ≈ 100% copper and multilayer regions and with the nearest-neighbor spacing near that of the matrix.
91 citations
TL;DR: Linearly polarized synchrotron radiation has been used to investigate the orientation dependence of the K absorption edge of a single crystal of ammonium dithiomolybdate, the crystal structure of which is also reported in this article.
Abstract: Linearly polarized synchrotron radiation has been used to investigate the orientation dependence of the K absorption edge of a single crystal of ammonium dithiomolybdate, the crystal structure of which is also reported herein. Following the collection of spectra with the polarization vector parallel to the oxygen-oxygen interatomic vector, the sulfur-sulfur vector, and the twofold rotation axis, self-consistent field X..cap alpha.. multiple scattered wave (SCF X..cap alpha.. MSW) calculations were done to interpret the observed orientation dependence. It is shown that this orientation dependence can be used to highlight the edge features which derive from molecular orbitals contributed to principally by the oxygen of the sulfur ligands. Anisotropy is also apparent in the extended X-ray absorption fine structure (EXAFS) spectra, which were recorded for orientations along the S-S and O-O interatomic vectors. It is thus demonstrated that polarized single-crystal X-ray absorption spectroscopy can provide orientationally selective information about the absorbing atom. It could, in principle, be used to deduce certain types of geometric information about the x-ray absorbing species.
76 citations
TL;DR: In this paper, it was shown that the problem of determining the function of radial atomic distribution around an absorbing atom by oscillations of the X-ray absorption coefficient belongs to a family of incorrect problems.
Abstract: It is shown that the problem of determining the function of radial atomic distribution around an absorbing atom by oscillations of the X-ray absorption coefficient belongs to a family of incorrect problems. A regularization algorithm is proposed for the problem concerned. Computational schemes realized involving the use of computers are described. Some results of model calculations are given.
Es wird gezeigt, das das Problem der Bestimmung der radialen atomaren Verteilungsfunktion um ein absorbierendes Atom durch Oszillationen des Rontgenabsorptionskoeffizienten zur Familie der inkorrekten Probleme gehort. Ein Regulierungsalgorithmus wird fur das betrachtete Problem vorgeschlagen. Realisierte Berechnungsschemata, die die Benutzung von Computern einschliesen, werden beschrieben. Einige Ergebnisse von Modellberechnungen werden mitgeteilt.
67 citations
TL;DR: In this paper, an investigation was conducted of the extended x-ray absorption fine structure (EXAFS) associated with the Liii absorption edge of osmium and the K absorption edge in silica supported the presence of bimetallic clusters of Osmium-copper catalysts.
Abstract: An investigation was conducted of the extended x‐ray absorption fine structure (EXAFS) associated with the Liii absorption edge of osmium and the K absorption edge of copper in silica supported osmium–copper catalysts with a 1:1 atomic ratio of copper to osmium. The effect of the copper on the Liii x‐ray absorption threshold resonance of the osmium was also investigated. Chemisorption and catalysis studies had earlier indicated a strong interaction between osmium and copper in such catalysts, and led to the proposal that bimetallic clusters of osmium and copper were present on the silica. Information on the structure of the osmium–copper clusters has been obtained from the EXAFS data of the present investigation. The osmium atoms in the clusters are coordinated to a large extent to other osmium atoms, whereas the copper atoms are coordinated extensively to osmium atoms as well as to copper atoms. The results are consistent with a model in which the copper in the clusters is present at the surface and are ...
TL;DR: In this article, the Extended X-ray Absorption Fine Structure (EXAFS) of oxygen on Al(111) at submonolayer coverages was derived for both the chemisorbed phase characterized by a 14 eV chemical shift of the Al 2p level and the oxide-like phase formed upon heating and exhibiting a 27 eV shift.
01 Jan 1981
TL;DR: Extended X-ray Absorption Fine Structure (EXAFS) refers to oscillations of the Xray absorption coefficient on the high energy side of an absorption edge and may have a magnitude of 10% or more.
Abstract: Extended X-ray Absorption Fine Structure (EXAFS) refers to oscillations of the X-ray absorption coefficient on the high energy side of an absorption edge. Such oscillations can extend up to 1000 eV above the edge and may have a magnitude of 10% or more. This phenomenon has been known for half a century and the basic physical explanation has been provided by Kronig1 as being due to modification of the final state of the photoelectron by atoms surrounding the excited atom. More recent work has established that a single scattering short-range order theory is adequate under most circumstances.
TL;DR: In this paper, an iterative fitting algorithm was designed to minimize the difference between the experimental data and an ab initio theoretical calculation of the unapproximated (curved wave) EXAFS expression.
Abstract: The extended X-ray absorption fine structure (EXAFS) of a series of lithium germanate glasses were obtained using synchroton radiation. Structural parameters were extracted from the data using an iterative fitting algorithm designed to minimize the ‘sum of squares’ difference between the experimental data and an ab initio theoretical calculation of the unapproximated (‘curved wave’) EXAFS expression. We identify two distinct co-ordination sites in the glasses with germanium-oxygen bond lengths which correspond closely to the bond lengths found in the crystalline forms of germanium dioxide. With the additional assumption that these sites are four-fold and six-fold co-ordinated, we conclude that the ratio of six-fold to four-fold sites increases with the addition of alkali oxide, up to a maximum of around 34%.
TL;DR: In this article, the relationship of the extended X-ray absorption fine structure (EXAFS) to the fine structure observed in the reflectivity above K edge energy is discussed in view of the evaluation of structural parameters of the surface near regions from reflectivity spectra.
Abstract: The reflectivity of a polycrystalline thin Cu film has been measured around the critical angle of total reflection and around the Cu K edge energy. The relation of the extended X-ray absorption fine structure (EXAFS) to the fine structure observed in the reflectivity above K edge energy is discussed in view of the evaluation of structural parameters of the surface near regions from the reflectivity spectra. The analysis of reflectivity fine structure spectra can be performed by techniques developed for the investigation of EXAFS spectra with additional phaseshift and amplitude functions entering the analysis of the reflectivity spectra. These quantities have been calculated from experiment and agree well with theory. The next-nearest Cu-Cu bond length in the surface region of Cu has been found to agree with the bulk value to within 0.01 AA.
TL;DR: In this article, the optical absorption spectra of small particles of α-, β-, and x-form of metal-free phthalocyanine (H2Pc), surrounded by a dielectric (polymers) have been studied.
Abstract: The optical absorption spectra of small particles of α-, β-, and x-form of metal-free phthalocyanine (H2Pc) and vanadyl phthalocyanine (VOPc) surrounded by a dielectric (polymers) have been studied. The true bulk absorption can be obtained by measuring the difference in transmittance of two films of identical composition but different thicknesses. This approach eliminates effectively light reflection losses. Comparison between the absorption spectra measured by direct vs. difference in transmittance revealed a number of differences: shift in the absorption frequencies, change in absorption intensities, and change in peak-to-valley ratio. These differences are due to light scattering which can be significantly minimized by using the differential transmittance method. The true peak absorption of x-H2Pc particles located at 770 and 615 nm had an absorption coefficient of 35.3 and 34.2 μm−1, respectively. The absorption minimum occurs at 477 nm. The peak-to-valley ratio was 27.The absorption spectra of VOPc p...
TL;DR: In this article, the elastic core effect of Al-Mg and Al-7 was measured on the magnesium $K$ edge using the soft-x-ray beam delivered by the ACO (Anneau de Collision d'Orsay) storage ring, as well as the extended x-ray absorption fine structure (EXAFS) spectra of elemental aluminium (1556 eV) and magnesium.
Abstract: The extended x-ray absorption fine structure (EXAFS) spectra of Al-3 at.% Mg and Al-7 at.% Mg have been measured on the magnesium $K$ edge (1303 eV) using the soft-x-ray beam delivered by the ACO (Anneau de Collision d'Orsay) storage ring, as well as the EXAFS of elemental aluminium (1556 eV) and magnesium. With the use of quasiexperimental phase shifts determined from aluminum and magnesium data, the first-shell radius around a magnesium impurity in an Al-Mg alloy has been determined within \ifmmode\pm\else\textpm\fi{}0.015 \AA{}, yielding a direct measurement of the elastic core effect which turns out to be large \ensuremath{\sim}0.08 \AA{}. It is discussed in the framework of the elastic theory of continuous media and of the lattice static method, both of which fail to give the correct magnitude of the local relaxation.
TL;DR: Using synchroton radiation, the calcium K-edge extended x-ray absorption fine structure (EXAFS) for a number of calcium-containing solids of biological interest was measured as discussed by the authors.
TL;DR: The beat pattern observed in the extended x-ray absorption fine structure can be accounted for only by postulating a combination of sulfur and nitrogen (or oxygen) ligands to the copper.
Abstract: The copper x-ray fluorescence excitation spectrum of cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) has been recorded in the 245—270 K range. The beat pattern observed in the extended x-ray absorption fine structure can be accounted for only by postulating a combination of sulfur and nitrogen (or oxygen) ligands to the copper. The average Cu—S distance is 2.27 ± 0.02 A and the average Cu—N (or Cu—O) distance is 1.97 ± 0.02 A. The amplitudes require ca, 1-1.5 sulfurs and 2 nitrogens (or oxygens) per copper. The distribution of sulfur ligands between CuA and CuB sites is not known, although there is some evidence that two sulfur atoms are bound to CuA.
TL;DR: Comparison of the results shows that bone mineral is appreciably different from crystalline synthetic hydroxyapatite and geological apatites, which are similar to each other, but closely resembles hydroxyAPatite obtained by maturation of amorphous calcium phosphate.
TL;DR: In this article, the Auger-assisted desorption process was shown to be a surface-, site-, and adsorbate-specific probe of electronic and geometric surface structure applicable to a wide range of systems.
TL;DR: In this article, the optical absorption of Cd1−xMnxTe crystals was measured as a function of temperature and Mn content, and the negative temperature coefficient was discussed in terms of possible absorption mechanisms different from the interband transitions which dominate the absorption for lower Mn concentrations.
01 Jan 1981
TL;DR: Extended X-ray absorption fine structure (EXAFS) as discussed by the authors refers to the oscillatory variation of the Xray absorption as a function of photon energy beyond an absorption edge.
Abstract: Extended X-ray absorption fine structure (EXAFS) refers to the oscillatory variation of the X-ray absorption as a function of photon energy beyond an absorption edge. The absorption, normally expressed in terms of absorption coefficient (µ), can be determined from a measurement of the attenuation of X-rays upon their passage through a material. When the X-ray photon energy (E) is tuned to the binding energy of some core level of an atom in the material, an abrupt increase in the absorption coefficient, known as the absorption edge, occurs. For isolated atoms, the absorption coefficient decreases monotonically as a function of energy beyond the edge. For atoms either in a molecule or embedded in a condensed phase, the variation of absorption coefficient at energies above the absorption edge displays a complex fine structure called EXAFS.
TL;DR: The photoacoustic spectra in several semiconductors such as Si, Ge, InSb, GaAs, and GaP have been measured in the region of wavelength shorter than the fundamental absorption edge, where the PA signal is regarded to be independent of the absorption coefficient as discussed by the authors.
Abstract: The photoacoustic (PA) spectra in several semiconductors such as Si, Ge, InSb, GaAs, and GaP have been measured in the region of wavelength shorter than the fundamental absorption edge, where the PA signal is regarded to be independent of the absorption coefficient. We found the dips in the PA spectrain this region which can be ascribed to the optical reflection effect inherent to the band structure.
TL;DR: In this paper, the pair absorption coefficient for the colliding Xe atoms of the molecular fluorine laser radiation was found to be α = (4.32 ± 0.1) × 10-9Torr-2cm-1.
TL;DR: Extended X-ray absorption fine structure (EXAFS) results for amorphous and crystalline Ge at temperatures ranging from 83 to 1085 K were presented in this article.
Abstract: Extended X-ray absorption fine structure (EXAFS) results are presented for amorphous and crystalline Ge at temperatures ranging from 83 to 1085 K. Specific tests for the detection of asymmetry in t...
TL;DR: In this article, a Michelson-type Fourier transform interferometer was used to obtain HNO3 spectral spectra with path lengths of 10.3, 25.5, and 49.8 cm at temperatures of 240, 248, 283, and 294 K. The measurements lead to a total band intensity value of 642 plus or minus 5% per sq cm amagat.
Abstract: Laboratory spectra have been obtained for HNO3 with a Michelson-type Fourier transform interferometer using absorption cells with path lengths of 10.3, 25.5, and 49.8 cm at temperatures of 240, 248, 283, and 294 K. The measurements lead to a total band intensity value of 642 plus or minus 5% per sq cm amagat, which is a temperature independent value after the gas density correction has been made. However, the temperature dependence of the spectral absorption coefficients is apparent in the 885 kayser region.
TL;DR: The far-infrared absorption spectra of H 2 16 O, H 2 17 O, and H 2 18 O have been observed at resolutions up to 0.015 cm −1 and path lengths up to 13 m as discussed by the authors.