X-ray absorption spectroscopy

X-ray absorption spectroscopy (XAS) is a widely used technique for determining the local geometric and/or electronic structure of matter.

[2] XAS data is obtained by tuning the photon energy,[3] using a crystalline monochromator, to a range where core electrons can be excited (0.1-100 keV).

The edges are, in part, named by which core electron is excited: the principal quantum numbers n = 1, 2, and 3, correspond to the K-, L-, and M-edges, respectively.

There are three main regions found on a spectrum generated by XAS data which are then thought of as separate spectroscopic techniques (Figure 2): XAS is a type of absorption spectroscopy from a core initial state with a well defined symmetry; therefore, the quantum mechanical selection rules select the symmetry of the final states in the continuum, which are usually a mixture of multiple components.

The most obvious means of mapping heterogeneous samples beyond x‐ray absorption contrast is through elemental analysis by x‐ray fluorescence, akin to EDX methods in electron microscopy.

Figure 1: Transitions that contribute to XAS edges
Figure 2: Three regions of XAS data for the K-edge