XANES backscattering amplitude

Final detennination of the structure was made by proposing a structural model with Cu sitting in threefold hollow sites and O atoms on atop sites with respect to the Cu atoms (Fig. 27.16). A program, FEFFIT, was used to analyze the data (Stem et al., 1995). This calculates the phase and amplitude parameters for the various backscatters. The EXAFS for the parallel polarization could be fitted six Cu-Cu interactions at a bond distance of 2.67 A and three Cu-Pt interactions at 2.6 A. For the perpendicular polarization, the data could be fitted one Cu-0 interaction at 1.96 A and three Cu-Pt interactions at 2.6 A. The Cu-Pt bond length is shorter than the sum of the metallic radii of Cu and Pt, which is 2.66 A. This indicates a Cu oxidation state different from zero, which agrees with the XANES results. 

The intensity of the EXAFS osdllation is dependent on a number of factors. First, the number and nature of backscattering atoms is a major contributor to the intensity of the oscillations. Different absorbers have different backscattering powers so the amplitude is dependent on the element which is the next nearest neighbor to the absorber atom. Depending on the absorber and the system, not all ejected electrons take part in the scattering process-up to 30% of the photoelectrons go into shake-up/down processes and are not available for EXAFS or XANES spectroscopy (see below). 

---