Röntgenabsorptiospektroskopia

Röntgenabsorptiospektroskopia, often abbreviated as XAS, is a spectroscopic technique used to investigate the elemental composition and electronic structure of materials. It relies on the absorption of X-rays by atoms in a sample. When X-rays of a specific energy strike an atom, they can excite an electron from a core energy level to a higher energy state or even eject it from the atom. The energy required for this excitation is characteristic of the element and the specific electronic shell involved.

The technique measures the amount of X-ray absorption as a function of X-ray energy. Typically, a beam of tunable X-rays is passed through a sample, and the transmitted intensity is measured. The resulting spectrum shows sharp increases in absorption, known as absorption edges, at energies corresponding to the binding energies of core electrons. Above the absorption edge, the absorption coefficient generally decreases with increasing energy, but it can exhibit fine structures called X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS).

XANES provides information about the oxidation state and local coordination geometry of the absorbing atom. EXAFS, occurring at higher energies, reveals details about the distances and types of neighboring atoms to the absorbing atom, essentially mapping out the local atomic environment. XAS is a non-destructive technique and can be applied to a wide range of materials, including solids, liquids, and gases, and is widely used in fields such as materials science, chemistry, physics, and biology for elemental analysis and structural determination.