röntgenabsorptiometrillä

Röntgenabsorptionsspektroskopie, often abbreviated as XAS, is a powerful spectroscopic technique used to investigate the electronic and structural properties of matter. It relies on the interaction of X-rays with atoms. When X-rays of specific energies are incident on a sample, electrons in the core shells of atoms can absorb these X-rays, leading to their excitation to higher energy levels or their ejection from the atom. This absorption process is highly dependent on the energy of the incident X-rays and the chemical environment of the absorbing atom.

The core principle of XAS is to measure the absorption of X-rays as a function of their energy. By scanning the X-ray energy across the absorption edge of a particular element, a spectrum is generated that contains valuable information. Near an absorption edge, which corresponds to the binding energy of a core electron, the absorption coefficient of the material changes dramatically. The fine structures observed above and below the absorption edge provide insights into the local atomic structure, oxidation state, and bonding characteristics of the absorbing element.

XAS can be broadly divided into two main regions: X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS). XANES, occurring at energies close to the absorption edge, is sensitive to the oxidation state and local coordination geometry. EXAFS, observed at higher energies beyond the absorption edge, provides information about the distances to neighboring atoms, their identity, and their number. This makes XAS a versatile tool applicable in fields such as materials science, chemistry, physics, biology, and environmental science for characterizing a wide range of samples, including solids, liquids, and gases.