DAFS ANALYSIS METHODS

For the work described in this chapter, systems with well known structures were chosen so we could demonstrate the enhanced sensitivities of DAFS. The goals of the DAFS analysis were to isolate the fine structure oscillations and, from them, to obtain the detailed wavevector and site selected XAFS-like short-range order information and XANES-like structural, valence and empty orbital information. This section describes the methods that we have developed to isolate the DAFS signals and to analyze the isolated signals. The main steps are listed schematically:

1. Measure the Bragg intensities versus photon energy and apply the standard absorption and diffraction corrections.

   (a) Measure and subtract the background.

   (b) Apply the area, Lorentz-polarization, instrument and absorption corrections.

   (c) Remove any Bragg glitches from the XAFS and determine .

2. Isolate the fine structure using method 2a or 2b.

   (a) Isolate the effective fine structure term directly from the diffracted intensity using spline methods analogous to conventional XAFS analysis.

   (b) Impose the Kramers-Kronig relation between the real and imaginary components of the DAFS signal, and use an iterative method to extract the real and imaginary components, f'(E) and f''(E), from the data.

3. Use FEFF to analyze the isolated fine structure signals.

The following subsections describe some of the important aspects of these analysis methods. The detailed analysis procedures are described in reference [11].

 
• Absorption corrections
• Two methods of isolating the diffraction fine structure
  • The direct spline method
  • The iterative Kramers-Kronig method
• FEFF analysis of the isolated EDAFS oscillations
• Information content of DAFS compared to XAFS