EXAFS

Shell fitting of extended X-ray absorption fine structure (EXAFS) is commonly done in Artemis, part of the Demeter package. Athena turns an experimental spectrum into a file Artemis can import. Artemis then lines the measured oscillation up with scattering paths from FEFF, and from that estimates the coordination number $N$, a distance correction, the disorder $\sigma^2$, and the energy-origin shift $\Delta E_0$. The interface, the order of operations, and three examples are kept apart below....

Synchrotron radiation (SR) and X-ray absorption spectroscopy (XAS) are often mentioned together, but they are not the same object. A synchrotron is a light source. XAS is an experiment that uses X-rays interacting with matter to analyse a sample. The synchrotron: a source of tunable X-raysSynchrotron radiation is the electromagnetic radiation emitted along the tangent when a fast charged particle is deflected in a magnetic field. In 1947, researchers saw the intense radiation produced when hi...

An XAS scan from low energy to high energy looks like a flat line, then a step, then a wobble. The usual split is: XANES (X-ray absorption near-edge structure): the pre-edge, the edge, and roughly the first 50 eV above it. EXAFS (extended X-ray absorption fine structure): the decaying oscillations from about 50 eV above the edge out to several hundred electronvolts. In soft X-ray and surface-science papers, the near-edge region is often called NEXAFS (near-edge X-ray absorption fine structu...