X-Ray Absorption Fine Structure (XAFS) Spectroscopy - A Review

Abstract

X-ray absorption spectroscopy (XAS) refers to the details of how X-rays are absorbed by an atom at energies near and above the core-level binding energies of that particular atom. The absorption of X-rays on the high energy side of absorption edges does not vary monotonically in condensed matter but has a complicated behavior which extends past the edge up to about ~1 keV. This non-monotonic variation has received the name of X-ray absorption fine structure (XAFS). The X-ray absorption fine structure is typically divided into two regimes: X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). This review describes the basic phenomenon of XAFS, theory of EXAFS and the method of extracting structural parameters by EXAFS which relate to the local environment surrounding the absorbing atom. Also, it has been pointed out that XANES can be used to extract information about the oxidation state, three dimensional geometry, and coordination environment of elements under investigation. There are numerous examples of the applications of the XAFS in various fields in the literature. Some selected examples are cited here and discussed so as to give the reader a glimpse of the usefulness and versatility of the XAFS. The two types of EXAFS beamlines available at the synchrotron facilities have been described. The details of BL-8 dispersive EXAFS beamline at 2 GeV Indus-2 synchrotron source at Raja Ramanna Center for Advanced Technology (RRCAT), Indore, India have been given. For the last fifty years research workers in India have been doing XAFS experiments on laboratory set-ups. Now, it is hoped that research workers from Indian laboratories will do experiments on synchrotrons. Hence, details regarding experiment and analysis of the XAFS data have been given in this review so that any one who wants to do research work in the field of XAFS may get necessary information at one place. This is important because the EXAFS beamlines at the Indus-2 synchrotron have become easily available to Indian workers which were not available until now.