Quantum Mechanics/X-Ray Diffraction Techniques/XANES

XANES or X-Ray Absoption Near Edge Structure is an X-Ray abosorption technique. The tehchnique allows for the study of the chemical species in the sample and the concentration. The use of high energy X-Rays is available at syncrotron sources around the world. The older 2nd generation light sources are strong enough to provide for excellent analysis. However, EXAFS is demanding of the newer 3rd generation light sources such as APS.

Edge energy range
In the absorption edge region of metals the photoelectron is excited to the first unoccupied level above the Fermi level. Therefore its mean free path in a pure single crystal at zero temperature is as large as infinite, and it remains very large increasing the energy of the final state up to about 5 eV above the Fermi level. Beyond the role of the unoccupied density of states and matrix elements in single electron excitations, many-body effects appear as an "infrared singularity" at the absorption threshold in metals.

In the absorption edge region of insulators the photoelectron is excited to the first unoccupied level above the chemical potential but the unscreened core hole forms a localized bound state called core exciton.