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What is X-ray Absorption Spectroscopy?
X-ray absorption spectroscopy (XAS) is an analytical technique that relies on the variable absorption of x-rays by matter to probe its chemical state and local structure. A beam of x-rays of nearly one energy is put onto a sample, and the change in x-ray absorption is measured as the energy of the beam is varied.
For each element of the periodic table, every electron shell in an atom of that element has a unique energy required to eject it from the atom. In an XAS measurement, the energy of the incident x-rays is first tuned just below the energy of a particular electron shell, then the energy is gradually increased until eventually the x-ray has enough energy to eject that electron and is absorbed.
