Introduction to EXAFS

 

 

This page gives a short introduction to the EXAFS phenomenon, its causes and the process of data analysis. Users familiar with these topics can directly move on to Tutorial Overview by clicking on the right arrow.

 

What is EXAFS?

 

EXAFS (Extended X-ray Absorption Fine Structure) is the oscillating part of the X-ray Absorption Spectrum (XAS) that extends to about 1000 eV above an absorption edge of a particular element of a sample.

 

What causes EXAFS?

 

Electrons are knocked out of an atom when the energy value of incident X-rays surpasses the ionization threshold (the edge energy). The interference of these outgoing photoelectrons with the scattered waves from atoms surrounding the central atom causes EXAFS. The regions of constructive and destructive interference are respectively seen as local maxima and minima giving rise to the oscillations in EXAFS.

 

 

Significance of EXAFS

 

EXAFS gives us information about

·         Distances between central and neighboring atoms.

·         The number of neighboring atoms.

·         The nature of neighboring atoms (their approximate atomic number)

·         Changes in central-atom coordination with changes in experimental conditions

 

The main advantage of EXAFS analysis over X-ray Crystallography is that structures can be studied in non-crystalline forms (including liquid and frozen solutions).  Among other applications, EXAFS has proven helpful in studying the behavior of non-crystalline materials, environmental samples, and metallo-proteins in their naturally occurring states.

 

The EXAFS equation

 

Click anywhere on the equation to view explanation of the terms.

 

 

Additional resources

 

There is a lot of material on EXAFS available online. Below is a set of links that might be of interest.

 

The IXS (International XAFS Society) Home page

 

Grant Bunker's Tutorial on EXAFS

 

EXAFS Analysis Using FEFF and FEFFIT by Bruce Ravel

 

 

To start the Tutorial for EXAFS123, click on the right arrow.