X-ray Absorption Spectroscopy (XAS) is a technique that measures the absorption of X-rays as a function of energy. When X-rays are absorbed by a material, they excite core electrons to higher energy states. This process provides information about the local electronic and geometric structure around specific atoms in the material. XAS is divided into two regions: X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS).