Thirteen ways to read a XANES spectrum
The near-edge structure (XANES) of an X-ray absorption spectrum can be used to discuss the local chemical environment of the absorbing atom. The thirteen questions below are grouped as structure and speciation, quantitative analysis, and how a spectrum changes. The thirteen questions Approach What is observed Example or question Coordination edge and near-edge shape separate valence, coordination number, or geometry Crystallinity spectral shape crystalline versus amorphous $\mathrm{SiO...
A synchrotron is the light source; XAS is the measurement
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...
XANES and EXAFS: two ways to read one absorption spectrum
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...
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