New Perspectives in SEXAFS

In the past years SEXAFS has made significant contributions to the study of ordered overlayers on substrates. This has been possible by exploiting two powerful characteristics of the SEXAFS technique: atom specificity and bond orientation sensitivity. The intrinsic anisotropy of an ordered interface makes full use of the polarization dependence of the photoabsorption cross section, whereas the (ad)atom specificity inherently provides surface sensitivity. Nevertheless, such SEXAFS studies of ordered overlayers do not utilize another important feature of EXAFS spectroscopy, i. e., the short-range character which makes it possible to study disordered systems. Recently, results(1) from reactive interfaces have shown that SEXAFS can determine site geometries in disordered systems without the assistance of polarization dependence. This is a marked departure from previous studies on ordered overlayers where the polarization dependence has played an important role for structure determination.