X-ray absorption spectroscopy

The X-ray absorption spectroscopy is currently a widely used technique giving information on the local structure and on the electronic states in gas-phase, molecular and condensed matter.

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X-ray absorption spectra are obtained by tuning the photon energy in a range where bound electrons can be excited (0.1-100 keV photon energy). This technique is usually applied at synchrotron radiation facilities providing intense and tunable x-ray beams.

Different acronyms are currently used in the literature depending on the particular applications therefore more details on methods, technique, and significance can be found searching XAFS (X-ray Absorption Fine Structure) or EXAFS (Extended XAFS).

The spectral region near a core excitation (near-edge region) is usually called XANES (x-ray absorption near-edge structures) or NEXAFS (Near-Edge X-ray Absorption Fine Structure).

Applications

XAS is an experimental technique used in different scientific fields including molecular and condensed matter physics, material science, chemistry, earth science, biology, and more. In particular, its unique sensitivity to the local structure, as compared to x-ray diffraction, have been exploited for studying:

• glass, amorphous and liquid systems
• solid solutions
• Doping and ionic implantation materials for electronics
• local distortions of crystal lattices
• organometallics compounds
• metalloproteins
• metal clusters
• vibrational dynamics
• ions in solutions
• speciation of elements

History

An informative account about the history of XAS and EXAFS (originally called Kossel's structures) is given in the paper "A History of the X-ray Absorption Fine Structure} by R. Stumm von Bordwehr", Ann. Phys. Fr. vol. 14, 377-466 (1989) (author's name is C. Brouder).

Relevant Websites

• International XAFS Society, official organization promoting XAS
• FEFF Project, University of Washington, Seattle
• GNXAS project and XAS laboratory, Università di Camerino