The method is based on the absorption of X-ray photons by the studied materials. When the energy of the incident photons approaches the excitation energy of electrons in certain atoms (absorption edge), the absorption coefficient rises significantly. This energy is characteristic for a given element and electronic shell, therefore the method can be used to study the chemical composition of the complex compounds. Thanks to the subtle variation of the absorption coefficient near the absorption edge, which can be probed by varying the energy of the incoming X-ray radiation, chemical properties (such as oxidation state) and local geometric arrangement of the atoms surrounding probed element (distance to the nearest neighbors and their number) can be studied.

Depending on the choice of a detection method, signal can be collected either from the surface of the samples (depth up to a few nanometers, in case of the total electron yield detection), or from the bulk (depth from a few hundred nanometers, when using soft X-ray radiation up to a few hundred micrometers, when using hard X-ray radiation, in case of the fluorescence or transmission detection). It is also possible to study time-dependent change in the adsorption coefficient of the studied materials.

XAS method can be used in the following industrial sectors:

• catalysis (local structure of the catalytic active sites, chemical reactions and their optimization, ageing and regeneration of the catalysts)
• thin films and coatings (chemical reactions in the anti-corrosion coatings, studying the deposition and ageing of various coatings)
• environmental engineering (deactivation of the toxic substances, identification and quantification of heavy metals in the environment, applications of the biomass to absorb heavy or precious metals)
• biomaterials (local structure and the interactions of various biomaterials, structure and properties of biopolymers, hydrogels, biosorption processes)
• pharmaceutics (bioavailability and interactions of drugs with the environment, accumulation of drugs in tissues, local structure of the active substances).

XAS method is available on the following beamlines: ASTRA, DEMETER, PHELIX, PIRX. The basic parameters of the experimental stations and restrictions with regard to sample type are shown in table.