Extended X-ray absorption fine structure

About: Extended X-ray absorption fine structure is a research topic. Over the lifetime, 10452 publications have been published within this topic receiving 276744 citations.

Absorption Spectra in Irradiated Water and Some Solutions: Absorption Spectra of ‘Hydrated’ Electron

Abstract: The absorption spectra of aqueous solutions after exposure to a pulse of 1.8 Mev electrons reveal a broad transient absorption band that is believed to be due to the hydrated electron, the existence and properties of which are predicted by Platzman. Aqueous ammonia solutions of various concentrations are exposed to 1.8 Mev electrons and their absorption spectra observed. The transient spectrum observed is assumed to be due to an electron trapped in the water. (D.C.W.)

Infra-red Absorption in Semiconductors

Abstract: Infra-red absorption in semiconductors is classified into four different types according to the mechanism: (i) intrinsic absorption associated with electron excitation across the energy gap; (ii) absorption due to the presence of free carriers; (iii) absorption associated with impurities or lattice defects; and (iv) absorption associated with lattice vibration. A general introduction is followed by some theoretical discussions. Electron excitation between different energy bands is discussed with emphasis on the intrinsic absorption edge. For the absorption by free carriers, the effects of electron scattering by lattice vibration and by impurity centres are considered. Absorption associated with localized electronic states is briefly discussed. Experimental results are discussed for four different semiconductors: germanium, silicon, indium antimonide, and tellurium. All four types of absorption have been investigated to some extent for germanium and silicon. The work done on these materials provides a pattern for infra-red studies on semiconductors. The absorption edge in indium antimonide is affected by the carrier concentration. Long wave-length absorption shows interesting behaviour, and the observed effects attributed to lattice vibration have provided information regarding the type of binding in the crystal. Tellurium, having an optical axis, is doubly refracting. Both the absorption edge and the absorption associated with free carriers depend on the direction of polarization of the radiation.

EXAFS Studies on the Size Dependence of Structural and Dynamic Properties of CdS Nanoparticles

Abstract: Size-dependent structural and dynamic properties of CdS nanocrystals with 13−120 A diameter and of molecular crystals consisting of three-dimensional superlattices of these nanoparticles have been determined by extended X-ray absorption fine structure spectroscopy (EXAFS) at the Cd K edge at temperatures between 5 and 290 K. It is shown that these properties are governed by the surface-to-volume ratio and the way of surface stabilization of the nanoparticles. Thiol-capped CdS nanoparticles with diameters from 13 to 40 A show an expansion of the mean Cd−S distance whereas mean interatomic distances in polyphosphate-stabilized particles with 30−120 A diameter are slightly contracted with respect to CdS bulk. By measuring the EXAFS spectra between 5 and 290 K, the total mean-square relative displacement could be separated into a static part which is independent of temperature and into a dynamic temperature-dependent part. The temperature-independent mean-square relative displacement (or static disorder) of t...

Zeeman Effects in the Edge Emission and Absorption of ZnO

Abstract: Of the more than 20 sharp characteristic emission and absorption lines observed in the edge emission and absorption spectra of ZnO platelets, several typical lines have been examined in detail experimentally at low temperatures (\ensuremath{\sim}1\ifmmode^\circ\else\textdegree\fi{}K). Zeeman effects, in magnetic fields up to 45 000 G, have been studied in singlets as well as zero-field-split doublets. In particular, the magnetic splitting of ${I}_{9}$ (an emission line appearing at 3692.64 \AA{}) has been studied as a function of magnetic field orientation (angular orientation of $c$ axis with respect to field direction). In accordance with the Thomas-Hopfield theory, arguments have been presented for the association of ${I}_{9}$ with a bound-exciton complex; this line has been observed to split linearly as a function of field strength, and an isotropic electron $g$ value of -1.93 has been determined at $C\ensuremath{\perp}\mathrm{H}$. The line ${I}_{9}$ is further characterized by an anisotropic hole $g$ value which has been determined to be -1.24 at $C\ensuremath{\parallel}\mathrm{H}$. A zero-field-split fluorescent doublet, ${I}_{2}\ensuremath{-}{I}_{3}$ (3680.63, 3681.59 \AA{}), which splits nonlinearly as a function of field strength, has been studied as a function of field orientation. The ${I}_{2}\ensuremath{-}{I}_{3}$ doublet has been attributed to an ionized exciton complex, and effective electron and hole $g$ values have been determined. Electron $g$ values are isotropic and essentially the same for all of the lines (about -1.95), while the hole $g$ value is not only anisotropic for each line, but also assumes different values in the different complexes (lines), indicating that the hole is sensitive to its state of binding in the exciton complex.

Electron Transfer Effects in Ozone Decomposition on Supported Manganese Oxide

Abstract: Manganese oxide catalysts supported on Al2O3, ZrO2, TiO2, and SiO2 supports were used to study the effect of support on ozone decomposition kinetics. In-situ laser Raman spectroscopy, temperature-programmed oxygen desorption, surface area measurements, and extended and near-edge X-ray absorption fine structure (EXAFS and NEXAFS) showed that the manganese oxide was highly dispersed on the surface of the supports. The EXAFS spectra suggested that the manganese active centers on all of the surfaces were surrounded by five oxygen atoms. These metal centers were found to be of a monomeric type for the Al2O3-supported catalyst and multinuclear for the other supports. The NEXAFS spectra for the catalysts showed a chemical shift to lower energy, and an intensity change in the L-edge features which followed the trend Al2O3 > ZrO2 > TiO2 > SiO2. The trends provided insights into the positive role of available empty d-states required in the reduction step of a redox reaction. The catalysts were tested for their ozon...