EXAFS FOR EVERYONE PDF

Background[ edit ] EXAFS spectra are displayed as plots of the absorption coefficient of a given material versus energy , typically in a — eV range beginning before an absorption edge of an element in the sample. The x-ray absorption coefficient is usually normalized to unit step height. This is done by regressing a line to the region before and after the absorption edge, subtracting the pre-edge line from the entire data set and dividing by the absorption step height, which is determined by the difference between the pre-edge and post-edge lines at the value of E0 on the absorption edge. These spectra can be used to determine the average oxidation state of the element in the sample. The XANES spectra are also sensitive to the coordination environment of the absorbing atom in the sample. Finger printing methods have been used to match the XANES spectra of an unknown sample to those of known "standards".

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Background[ edit ] EXAFS spectra are displayed as plots of the absorption coefficient of a given material versus energy , typically in a — eV range beginning before an absorption edge of an element in the sample. The x-ray absorption coefficient is usually normalized to unit step height.

This is done by regressing a line to the region before and after the absorption edge, subtracting the pre-edge line from the entire data set and dividing by the absorption step height, which is determined by the difference between the pre-edge and post-edge lines at the value of E0 on the absorption edge.

These spectra can be used to determine the average oxidation state of the element in the sample. The XANES spectra are also sensitive to the coordination environment of the absorbing atom in the sample. Finger printing methods have been used to match the XANES spectra of an unknown sample to those of known "standards". Linear combination fitting of several different standard spectra can give an estimate to the amount of each of the known standard spectra within an unknown sample. X-ray absorption spectra are produced over the range of — 35, eV.

The dominant physical process is one where the absorbed photon ejects a core photoelectron from the absorbing atom, leaving behind a core hole. The atom with the core hole is now excited.

The ejected photoelectron interacts with electrons in the surrounding non-excited atoms. If the ejected photoelectron is taken to have a wave -like nature and the surrounding atoms are described as point scatterers, it is possible to imagine the backscattered electron waves interfering with the forward-propagating waves.

The resulting interference pattern shows up as a modulation of the measured absorption coefficient, thereby causing the oscillation in the EXAFS spectra. The wavelength of the photoelectron is dependent on the energy and phase of the backscattered wave which exists at the central atom.

The wavelength changes as a function of the energy of the incoming photon. The phase and amplitude of the backscattered wave are dependent on the type of atom doing the backscattering and the distance of the backscattering atom from the central atom. The dependence of the scattering on atomic species makes it possible to obtain information pertaining to the chemical coordination environment of the original absorbing centrally excited atom by analyzing these EXAFS data.

Experimental considerations[ edit ] Since EXAFS requires a tunable x-ray source, data are always collected at synchrotrons , often at beamlines which are especially optimized for the purpose. The utility of a particular synchrotron to study a particular solid depends on the brightness of the x-ray flux at the absorption edges of the relevant elements.

Applications[ edit ] XAS is an interdisciplinary technique and its unique properties, as compared to x-ray diffraction, have been exploited for understanding the details of local structure in:.

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