1,721,011 research outputs found
Exact thermal and structural damping of the multiple scattering contributions to the XANES
No full textThermal and structural damping of the multiple-scattering contributions to the x-ray-absorption coefficient
No full textX-ray absorption spectroscopy and n-body distribution functions in condensed matter (I): theory
No full text
X-ray-absorption spectroscopy and n-body distribution functions in condensed matter .1. Theory
No full textThe general theoretical framework underlying the GNXAS multiple-scattering (MS) data-analysis method for x-ray absorption spectroscopy (XAS) is presented. The main approximations leading to the reduction of the many-body process in that of a photoelectron scattering in an effective potential are summarized. The methods available to expand the extended x-ray-absorption fine-structure chi(k) into physically meaningful terms are described, In particular, emphasis is given to the definition of the irreducible n-body signals gamma((n)) that can be calculated directly by means of linear combinations of continued fractions, or by using their respective multiple-scattering series. It is found that even for an infinite system the expansion of the chi(k) signal in terms of gamma((n)) has a better convergence rate than the MS series. Simple expressions for performing the configurational averages of the structural signals in the presence of thermal and structural disorder are derived. These can be used for the structural analysis of molecular, crystalline, or moderately disordered systems. It is shown that in the case of highly disordered systems the expansion in terms of the gamma((n)) signals is the natural framework for the interpretation of the XAS signal. General equations for the ensemble-averaged chi(k) signal as a function of a series of integrals over the n-body n > 2 distribution functions g(n) an provided and the possible use of advanced strategies for the inversion of the structural information is suggested
Structure of Oriented V2O5 Gel Studied by Polarized X-Ray-Adsorption Spectroscopy at theVanadium K Edge
No full textThe local structure around the vanadium site in the oriented V2O5⋅1.6 H2O dehydrated xerogel phase is investigated by polarized x-ray-absorption spectroscopy (XAS). A large dychroism is found both in the extended x-ray-absorption fine structure (EXAFS) and in x-ray-absorption near-edge structure (XANES). A joint analysis of EXAFS and XANES data is reported. EXAFS analysis has been performed using a spherical-wave propagator and XANES analysis by full multiple-scattering calculation. A detailed discussion about the origin of all the different features in the experimental XAS spectra and a method to extract small contributions in the EXAFS part of the spectrum is presented. Moreover, the local structure around the vanadium atom in the V2O5 hydrogel phase is derived
Orientational Disorder In Amorphous-silicon Probed By Xanes (x-ray Absorption Near Edge Structure)
No full textThe difference between the K-edges XANES (X-ray Absorption Near Edge Structure) spectra of crystal and amorphous silicon is discussed. We show that the multiple scattering signal gives a large contribution to the total absorption in crystalline silicon in an energy range of about 70eV. The double scattering term probing the triplet distribution function gives the major contribution to the XANES. We show that the difference between the crystalline and amorphous absorption spectra is due mainly to the crystalline multiple scattering signal which is quenched in the amorphous spectrum. The suppression of the signal due to the triplet distribution function in the amorphous silicon is assigned to the large orientational disorder
- …
