Anomalous X-Ray Scattering and its Relationship to EXAFS

Abstract

X-ray anomalous scattering techniques are described which utilize the strong energy dependence of the atomic scattering factor near an atom’s absorption edge to separate the total radial distribution function (RDF) into more species-specific distribution functions. Differential anomalous scattering (DAS) techniques and transmission EXAFS have been applied to sputtered amorphous Mo₄₂Ge₅₈ films. Although each approach yeilds, in principle, a description of the average coordination distances and numbers of the atomic species whose absorption edge is utilized, there is a significant discrepancy between the EXAFS radial structure functions (RSF) and the DAS differential distribution functions (DDF). The RSF’s indicate shorter first neighbor distances and markedly narrower first shells than do the DDF’s. The DDF’s show more distant coordination shells clearly, whereas the RSF’s do not. We attribute these differences to the different k-space ranges accessible to the two experiments and to the significant spreads in interatomic distances. With the combination of experiments, chemical short range order is demonstrated in this material.