Understanding EXAFS: The Role of Phase Correction and Analysis Tools

Extended X-ray Absorption Fine Structure (EXAFS) is a powerful technique used to study atomic structures and interactions in materials. A critical aspect of this methodology is phase correction, particularly through the backscattering phase shift of absorber-neighbor pairs. This process helps to correct the observed distances in the radial structure function while highlighting contributions from specific pairs of neighboring atoms, ensuring accurate structural interpretation.

In EXAFS analysis, the absence of phase correction can lead to substantial inaccuracies, such as peak positions in the radial structure function appearing approximately 0.5 Å too short. By applying the Fourier transform on the radial structure of a platinum (Pt) atom within a face-centered cubic (fcc) lattice, researchers can identify the arrangement and distances of surrounding atoms, typically observing a structured arrangement of neighbors across various shells.

Various software tools play a significant role in fitting EXAFS data to the theoretical models necessary for accurate interpretation. The University of Washington's UWXAFS package, Daresbury Laboratory's EXCURVE98, and the commercial XDAP program are among the most commonly utilized. Each software offers unique functionalities, from phase shift calculations to comprehensive fitting of experimental data using theoretical standards.

The FEFF program, for instance, conducts ab initio calculations of phase shifts and backscattering amplitudes, accommodating both single and multiple scattering events. This is crucial for constructing accurate theoretical models, especially in complex materials where higher coordination shells are involved. Meanwhile, EXCURVE98 integrates rapid curved wave theory for efficient data fitting in k-space and assesses error estimates, allowing researchers to refine their parameters systematically.

Finally, XDAP enhances the fitting process by utilizing both theoretically derived and experimentally obtained backscattering data. This flexibility helps in accurately characterizing the structures of reference compounds, ultimately leading to a deeper understanding of materials' properties. Access to a robust suite of EXAFS analysis programs underscores the importance of computational tools in complementing experimental techniques in material science research.