Showing papers on "Extended X-ray absorption fine structure published in 1976"
331 citations
TL;DR: In this article, the spectral-line absorption coefficient and radiative transfer expressions appropriate for calculating absorption and emission by atmospheric gases are formulated, and problems associated with the calculation of absorption by these two molecules are discussed.
Abstract: Publisher Summary This chapter focuses on absorption and emission by atmospheric gases. At centimeter and shorter wavelengths, absorption and emission by atmospheric gases can significantly affect the propagation of electromagnetic radiation through the atmosphere. At frequencies from 1 to 300 GHz, referred to as “microwave frequencies,” absorption by atmospheric gases is dominated by water vapor lines at 22 and 183 GHz, oxygen lines near 60 GHz and at 118 GHz, and relatively narrow and weaker ozone lines above 100 GHz. Non-resonant absorption by water vapor and oxygen has significant effects in the window regions away from the dominant lines. The radiative transfer expressions appropriate for calculating absorption and emission by atmospheric gases are formulated. The general expressions for the spectral-line absorption coefficient are provided, followed by specific expressions for calculating absorption by water vapor and oxygen. Problems associated with the calculation of absorption by these two molecules are discussed. The absorption by microwave lines of ozone and other minor constituents is considered. Finally, the results of calculations of atmospheric absorption and emission, as well as the measured values are presented in the chapter.
213 citations
TL;DR: In this article, optical transmission data covering the Γ15V−Γ1C absorption edge are presented, together with photoluminescence (PL) results, for AlxGa1−xAs crystals of high purity [n (293 K) <1017 cm−3] for 0
Abstract: Optical transmission data covering the Γ15V–Γ1C absorption edge are presented, together with photoluminescence (PL) results, for AlxGa1−xAs crystals of high purity [n (293 K) <1017 cm−3] for 0
172 citations
TL;DR: In this article, phase shifts in extended x-ray-absorption fine-structure (EXAFS) measurements have been empirically determined for atom pairs for photoelectron energies g 100 eV, which can be used with EXAFS spectra to determine interatomic distances typically to accuracies of 0.02 \AA{}.
Abstract: Phase shifts in extended x-ray-absorption fine-structure (EXAFS) measurements have been empirically determined for atom pairs. For photoelectron energies g 100 eV it is shown that these phase shifts, because they are essentially independent of chemical environment, can be used with EXAFS spectra to determine interatomic distances typically to accuracies of 0.02 \AA{}.
159 citations
TL;DR: In this article, the authors measured the extended x-ray absorption fine structure (EXAFS) from excitation of the adsorbed atom by monitoring the intensity of the Auger emission line as a function of photon energy and concluded that an average over a hemisphere outside the crystal is not sufficient to reduce the photoemission data to EXAFS.
Abstract: Novel methods for the determination of adsorbate position on surfaces based on final-state interference effects are discussed. The first is the measurement of extended x-ray absorption fine structure (EXAFS) from excitation of the adsorbed atom by monitoring the intensity of the Auger emission line as a function of photon energy. Such an experiment should be feasible with synchrotron radiation. The sensitivity of surface EXAFS to adatom position is demonstrated by calculations appropriate for adsorption of Se on several crystal faces of Ni. We also examine the possibility of measuring EXAFS by monitoring the photoelectron intensity and conclude that an average over a hemisphere outside the crystal is not sufficient to reduce the photoemission data to EXAFS. Relations between EXAFS and angular-resolved photoemission are elucidated and it is shown that the single scattering EXAFS theory includes second-order scattering from the excited atom in photoemission theory.
132 citations
TL;DR: The analysis of the results showed that the metals were present in two distinct phases: metallic with coordination and metal-to-metal distance characteristic of bulk Au, and Pt (particulate phase), and a highly disperse one (dissolved phase) as discussed by the authors.
66 citations
44 citations
TL;DR: In this article, the optical absorption spectra near the fundamental edge has been measured on high quality single crystals of BiI 3, and the absorption cross-section of the indirect transition is very large compared with that observed in indirect semiconductors and ionic crystals.
Abstract: The optical absorption spectra near the fundamental edge have been measured on high quality single crystals of BiI 3 . Above 50 K, the absorption coefficient near the edge is well described by the Urbach's rule. At lower temperatures, the corresponding transitions are of the allowed indirect type involving the creation of free excitons, and absorption components associated with three phonon energies have been resolved. The energies of the phonons are found to be 2.6±0.1, 7.1±0.2 and 13.4±0.4 meV. The absorption cross-section of the indirect transition is very large compared with that observed in indirect semiconductors and ionic crystals. These results are discussed in view of band nature of BiI 3 . Preliminary results on sharp absorption lines near the edge are also given.
42 citations
TL;DR: In this paper, the reflection spectra of BiI s single crystals were measured between 1.5 and 5.5 eV at 6, 77 and 286 K, and the intrinsic absorption coefficient and the real and imaginary parts of the dielectric constants were calculated.
Abstract: The reflection spectra of BiI s single crystals were measured between 1.5 and 5.5 eV at 6, 77 and 286 K. A Kramers-Kronig dispersion analysis of the data was made, and the intrinsic absorption coefficient and the real and imaginary parts of the dielectric constants were calculated. The large peak at 2.0 eV is ascribed to direct excitonic transition near the fundamental absorption edge. The main features observed in the absorption spectra are discussed in terms of two proposed models for anionic and cationic excitons in heavy metal halides. Measurements have also been made on the ordinary refractive index near the absorption edge. The data are well described by a two-oscillator model.
41 citations
TL;DR: In this article, the presence of NO2 absorption features in the ultraviolet, blue, and green regions of the optical spectrum has been considered in precision multiwavelength atmospheric turbidity studies.
Abstract: Nitrogen dioxide (NO2) has absorption features in the ultraviolet, blue, and green regions of the optical spectrum. Values of total columnar NO2 range from 0.4×10−3 to about 5×10−3 cm NO2 (STP) and yield optical depths from 0.008 to 0.087 at 390 nm, the wavelength of maximum absorption. The presence of NO2 absorption must be considered in precision multiwavelength atmospheric turbidity studies. Previous reported values of the Angstrom power law coefficient are probably too large because NO2 absorption was not accounted for.
41 citations
TL;DR: In this article, the dispersion of plasmon type excitations with dispersion between 3.8-4.5 and 8.0-12 eV was investigated.
TL;DR: In this paper, a new type of atomic absorption spectrometry using the Zeeman effect of sample materials is proposed, where a magnetic field was applied to the sample vapor in the direction perpendicular to the propagation of light emitted from an atomic spectral source.
TL;DR: In this paper, a similar fine structure to that in X-ray absorption spectra (EXAFS) is reported in electron energy loss spectra, which fit with the known structure for Al and Al2O3.
Abstract: A similar fine structure to that in X-ray absorption spectra (EXAFS) is reported in electron energy loss spectra. The results, which give an estimate of the interatomic distances for nearest-neighbour atoms, fit with the known structure for Al and Al2O3.
TL;DR: Saturation of optical absorption in InSb has been observed by using near absorption edge radiation of subnanosecond duration at 5.3μm to affect a wavelenght dependence on the optical absorption edge.
TL;DR: In this article, the non-atomic absorption signals obtained from alkali halides atomized from three types of graphite atomizer are examined, and the wavelength dependence of the signals identifies the absorption as that of charge-transfer transitions of the alkyl halide molecules.
TL;DR: In this paper, the authors investigated the nonlinear absorption of single picosecond light pulses (λ = 1.06 μm) in CdS at very high light intensities.
TL;DR: The technique of Doppler free two photon absorption was used to measure the fine structure interval in the 2D states of potassium for principal quantum numbers from 8 to 19 as discussed by the authors.
TL;DR: In this paper, the thickness effect is treated using a simplified form for the window function and the absorption edge and it is shown that for the low absorbing portion of the K edge the relative error caused by the tail of the window functions becomes larger, rather than vanishing, in the limit of zero thickness foils.
Abstract: The thickness effect is treated using a simplified form for the window function and the absorption edge. It is shown that for the low absorbing portion of the K edge the relative error caused by the tail of the window function becomes larger, rather than vanishing, in the limit of zero thickness foils. A means is described and experimentally demonstrated for separating changes in K absorption edge fine structure due to alloying from those due to the thickness effect.
TL;DR: A method for surface structure analysis is proposed, which provides a surface sensitive measure of the photoabsorption cross section in the media through measurement of the variations in the intensity of particular Auger lines as a function of the incident radiation energy.
Abstract: A method for surface structure analysis is proposed The proposed process combines x-ray photoabsorption and Auger electron emission The extended x-ray-absorption fine structure, occurring for photon energies above an atomic absorption edge, contains structural information of the microscopic environment due to the coupling of the photoelectron final state with the atomic initial state Measurement of the variations in the intensity of particular Auger lines, as a function of the incident radiation energy, provides a surface sensitive measure of the photoabsorption cross section in the media Theoretical considerations of the physical processes underlying the proposed experiment and its feasibility, and a discussion of background contributions are presented
TL;DR: In this paper, the absorption coefficient for intensive electromagnetic radiation is calculated for different scattering mechanisms in semiconductors: ionized impurities, polar and nonpolar optical interaction, deformation and piezoelectric interaction with acoustic phonons.
Abstract: The absorption coefficient for intensive electromagnetic radiation is calculated for different scattering mechanisms in semiconductors: ionized impurities, polar and nonpolar optical interaction, deformation and piezoelectric interaction with acoustic phonons — at any temperature using the path-integral method. The dependence on the intensity of partial multiphoton absorption coefficients as well as that of the total coefficient is investigated. In the cases of low and high temperatures the dependence of the absorption nonlinearity form on the scattering mechanism is studied. The possibility isrevealed to identify the dominant scattering mechanism on the base of experimental data on the nonlinearity of absorption.
[Russian Text Ignored].
TL;DR: In this article, the optical absorption spectra of the CuFeS 2 films were measured by means of the close-spacing chemical vapor deposition technique, and a distinctive feature of the spectrum is the existence of an absorption edge at 3.7 eV.
Abstract: The CuFeS 2 films were prepared by means of the close-spacing chemical vapor deposition technique, and the optical absorption spectra of the films were measured. Distinctive feature of the spectrum is the existence of an absorption edge at 3.7 eV in addition to a broad band located between 0.6 eV and 3.7 eV with a maximum around 2 eV. One can conclude from this observation that the absorption edge (0.6 eV) of CuFeS 2 reported previously is the foot of the `charge transfer' transition and that the extra absorption edge (3.7 eV) found in the present work corresponds to the fundamental absorption edge of the nonmagnetic analogs.
TL;DR: The infrared absorption coefficients of NaCl, KCl, NaF, CaF2 and BaF2 have been determined by calorimetric techniques at the laser wavelengths 1.06, 2.7, and 3.8 μm.
Abstract: The infrared absorption coefficients of NaCl, KCl, NaF, CaF2 and BaF2 have been determined by calorimetric techniques at the laser wavelengths 1.06, 2.7, and 3.8 μm. The absorption level of the best crystals can be 10−5 cm−1 or lower at l.06 μm, but no crystal with a coefficient lower than 10−4 cm−1 at 2.7 and 3.8 μm has been found. Possible reasons for these results are discussed.
TL;DR: In this article, the influence of the multimode structure of the radiation of a real laser on resonant many-photon processes (absorption of light and ionization of atoms) is analyzed.
Abstract: An analysis is made of the influence of the multimode structure of the radiation of a real laser on resonant many-photon processes (absorption of light and ionization of atoms). It is shown that the presence of many modes results in a radical modification of the absorption line profiles and in considerable changes of the frequency dependence of the ion yield (in the ionization case).
TL;DR: In this article, the K absorption spectra of chlorine in gaseous CH3Cl, C2H5Cl, CF2Cl2, and C 2H3Cl were recorded with a high resolving curved crystal spectrograph using the continuous radiation of a gold anode.
Abstract: The K absorption spectra of chlorine in gaseous CH3Cl, C2H5Cl, CF2Cl2, and C2H3Cl were recorded with a high resolving curved crystal spectrograph using the continuous radiation of a gold anode. The background radiation accompanying the bremsstrahlung was determined quantitatively. Thus absolute absorption cross sections could be evaluated. The absorption spectra consist of a Rydberg-like series of lines in which the third and higher components are not resolved. A theory for the interpretation of X-ray absorption spectra established by Wainstein et al. (1951) is discussed with regard to the experimental spectra obtained in this investigation.