XAFS studies of glass structure

X-ray absorption fine structure (XAFS) spectroscopy has become one of the most important techniques to characterise the local coordination of specific atomic species present in condensed matter. The possibility of investigating the structure of noncrystalline materials has made XAFS very attractive for the study of the short range structure of the glassy state. The XAFS acronym denotes the structure present above the x-ray absorption edges; such a structure is distinguished as x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS). XANES carries information on the atomic arrangement around the absorbing species: distances and bonding angles. XANES also provides information on the electronic states in the proximity of the conduction band: different chemical environments may be identified from known features in the spectrum. EXAFS provides information on the average distance and radial distribution function of the nearest neighbours of the absorbing species. In the last decade, the enormous progress of experimental techniques and the excellent quality of experimental spectra, consequent to the development of the synchrotron radiation facilities, have stimulated the evolution of the XAFS theory and analysis procedures. This paper is a survey on the theoretical development of XAFS and on the methods for determining the short range information in disordered materials. Applications of XAFS to some vitreous systems are reported.