Sexafs: New horizons in surface structure determinations

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Abstract
As early as the 1930s, it had been observed that the absorption cross section in the X-ray regime had a complex structure as a function of energy extending as far as 1000 eV above an absorption threshold.1 These measurements were made by using a low‐power conventional X-ray tube, a dispersive Bragg spectrometer, and film as a detector. After some correct and incorrect speculation concerning the origin of this extended X-ray absorption fine structure (EXAFS), the field remained essentially dormant through the 1950s. In the late 1960s the measurements were revived,2 this time using modern counting and automation techniques. The previous interpretation3–5 of the structure as arising from the backscattering of the ejected photoelectron from the atom near the absorbing site was strongly supported. The idea that this phenomenon might be used as a local structural probe was born. However, even with the experimental advances the measurements were difficult and time-consuming because of the low power of the X-ray source. This limited the application of the technique to highly concentrated systems and also inhibited the systematic study of the phenomenon that was necessary to turn the semiquantitative interpretations into quantitative evaluations.