Diffraction anomalous fine structure: Xafs with virtual photoelectrons

Abstract

This paper discusses a new x-ray structural technique, Diffraction Anomalous Fine Structure (DAFS), which combines the long-range order sensitivity of diffraction with the short-range order sensitivity and chemical selectivity of x-ray absorption (XAFS). Because absorption and scattering are related by causality, the absorption information available from XAFS is also accessible from DAFS measurements of the elastic, fixed momentum transfer, Bragg reflection intensities. These DAFS measurements exhibit a fine structure versus photon energy analogous to XAFS. DAFS provides all of the usual information of XAFS: the near neighbor bond lengths, numbers, types and disorders around the specifically excited atoms. In addition, because DAFS unifies all of the capabilities of diffraction and XAFS into a single technique, it provides advantages that neither technique possesses separately: (1) Spatial selectivity. DAFS provides short-range order information about the specific subset of long-range ordered atoms selected by the diffraction condition. (2) Site selectivity. DAFS provides site specific short-range order information for inequivalent sites of a single element. (3) Valence sensitivity. DAFS provides valence specific features in the near edge region. © 1993 The Japan Society of Applied Physics.