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EXAFS spectra are displayed as plots of the absorption coefficient of a given material versus energy, typically in a 500 – 1000 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.
EXAFS, resulting from the interference in the single scattering process of the photoelectron scattered by surrounding atoms, provides information on the local structure. Information on the geometry of the local structure is provided by the analysis of the multiple scattering peaks in the XANES spectra. The XAFS acronym has been later introduced ...
X-ray absorption near edge structure (XANES), also known as near edge X-ray absorption fine structure (NEXAFS), is a type of absorption spectroscopy that indicates the features in the X-ray absorption spectra of condensed matter due to the photoabsorption cross section for electronic transitions from an atomic core level to final states in the energy region of 50–100 eV above the selected ...
In the high kinetic energy range of the photoelectron, the scattering cross-section with neighbor atoms is weak, and the absorption spectra are dominated by EXAFS (extended X-ray absorption fine structure), where the scattering of the ejected photoelectron of neighboring atoms can be approximated by single scattering events.
It contains self-consistent real space multiple-scattering code for simultaneous calculations of x-ray-absorption spectra and electronic structure. Output includes extended x-ray-absorption fine structure ( EXAFS ), full multiple scattering calculations of various x-ray absorption spectra ( XAS ) and projected local densities of states ( LDOS ).
The fine structure energy corrections can be obtained by using perturbation theory.To perform this calculation one must add three corrective terms to the Hamiltonian: the leading order relativistic correction to the kinetic energy, the correction due to the spin–orbit coupling, and the Darwin term coming from the quantum fluctuating motion or zitterbewegung of the electron.
EvAX fits experimental EXAFS data by minimizing the difference between Morlet wavelet transforms [29] thus taking into account the representation of EXAFS spectra in k- and R-spaces simultaneously. The code accounts all important multiple-scattering paths with user-specified precision and is able to fit a single structure model to a set of ...
His research specialties are in condensed matter theory, particularly in the field of excited state electronic structure and the theory of X-ray and electron spectra. [ 8 ] [ 9 ] One of Rehr's major accomplishment was the theoretical solution of the EXAFS problem, [ 10 ] [ 11 ] and quantitative theories of core-level x-ray and electron ...