EXAFS backscattering power

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). 

Materials Characterization. Regarding education in the characterization or analysis of materials—a central topic of materials chemistry—there is a similar hierarchy of importance of subjects that chemistry students (and faculty) will need to have learned. Reference 7 treats this topic systematically, and Roy and Newnham (11) presented a comprehensive (albeit somewhat outdated) presentation of the architecture of materials characterization. Thus Rutherford backscattering and extended X-ray absorption fine structure (EXAFS) are excellent characterization research tools, but in the sequence of tools used every day on every sample, they are insignificant. Thus for structural characterization, X-ray powder diffraction reigns supreme, yet the full power of the modern automated search routines that can be universally applied are taught only to a minuscule fraction of even the materials science student body. 

X-ray absorption spectroscopy is a powerful tool for nanoparticle analysis due to its selectivity and independence of sample physical state. It is limited in range to the region within about 0.5-0.7 nm of a particular (chosen) absorber atom in the structure, but can be applied to amorphous or even liquid samples. The basic theory behind the origins and analysis of the extended X-ray absorption fine structure (EXAFS) has been well described by Sayers et al. (1970, 1971) and Lee et al. (1981). with mineralogical applications detailed by Brown et al. (1988). The crucial aspect of the EXAFS spectrum is that it is formed by an electron backscattering process in the vicinity of the absorber... 

For excitation from core states of atoms to a final continuum state in the solid, an important observation is the occurrence of quasiperiodic modulations in the intensity of the observed continuous spectrum. These modulations are readily explained as arising from interference between the wave of the escaping electron, and a backscattering off the nearest neighbour atoms. They are called extended X-ray absorption fine structure or EXAFS for short. They are very important, because they can be rather simply analysed to yield the distance between the atom on which the core excitation has taken place and its nearest neihbours. There is an extensive literature on this technique [643] which is a very powerful one, since it can be applied to all kinds of compounds each atom has its own particular, quasiatomic core states, and so the method is atom-specific. The only complication is when the same atom can occupy two different sites with different nearest neighbours. 

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