EXAFS Theory and Applications

X-ray absorption spectroscopy is a technique that depends on the absorption of the radiation by a selected type of atom within the material. A typical X-ray absorption spectrum is pictured in figure 7. The abrupt change in the absorption coefficient p, called absorption edge, occurs when the incident X-ray photon energy is sufficient to ionize an inner electron shell from the absorbing atom (K-edge when the ejected electron is a 1 s electron). 

Above this threshold, the absorption coefficient shows a modulation known as Extended X-ray Absorption Fine Structure (EXAFS). The origin of this modulation can be qualitatively explained as follows  

This modulation depends on the chemical nature of the neighbouring atonjs, the structural environment of these atoms and their distances to the absorber. 

Details of EXAFS theory and analysis are given in numerous reviews and books The main features only will be recalled in this paper. 

For moderate thermal or static disorders, the modulation of the absorption coefficient is given by  

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