X-ray absorption near edge structure

When the x-ray photon energy resonantly connects a core level with a narrow final state in a solid, such as an exciton, readily identifiable characteristic peaks will appear in the spectrum.

These narrow characteristic spectral peaks give the NEXAFS technique a lot of its analytical power as illustrated by the B 1s π* exciton shown in the second Figure.

The angle dependence of the x-ray absorption tracks the orientation of resonant bonds due to dipole selection rules.

Because soft x-rays are absorbed by air, the synchrotron radiation travels from the ring in an evacuated beam-line to the end-station where the specimen to be studied is mounted.

Specialized beam-lines intended for NEXAFS studies often have additional capabilities such as heating a sample or exposing it to a dose of reactive gas.

Beyond the role of the unoccupied density of states and matrix elements in single electron excitations, many-body effects appear as an "infrared singularity" at the absorption threshold in metals.

The fine structure in the x-ray absorption spectra in the high energy range extending from about 150 eV beyond the ionization potential is a powerful tool to determine the atomic pair distribution (i.e. interatomic distances) with a time scale of about 10−15 s. In fact the final state of the excited photoelectron in the high kinetic energy range (150-2000 eV ) is determined only by single backscattering events due to the low amplitude photoelectron scattering.

by the following relation: which means that for high energy the wavelength is shorter than interatomic distances and hence the EXAFS region corresponds to a single scattering regime; while for lower E,

Because NEXAFS can also determine the chemical state of elements which are present in bulk in minute quantities, it has found widespread use in environmental chemistry and geochemistry.

The acronym XANES was first used in 1980 during interpretation of multiple scattering resonances spectra measured at the Stanford Synchrotron Radiation Laboratory (SSRL) by A. Bianconi.

In 1982 the first paper on the application of XANES for determination of local structural geometrical distortions using multiple scattering theory was published by A. Bianconi, P. J. Durham and J.

The fundamental processes which contribute to XANES spectra: 1) photoabsorption of an x-ray into a core level followed by photoelectron emission, followed by either 2) (left) filling of the core hole by an electron in another level, accompanied by fluorescence; or (right) filling of the core hole by an electron in another level followed by emission of an Auger electron.
Normal-incidence boron 1s x-ray absorption spectra for two types of BN powder. The cubic phase shows only σ-bonding while the hexagonal phase shows both π and σ bonding.
Pictorial view of photoelectron scattering processes in the single-scattering regime, EXAFS (this assumes the single scattering approximation... multiple scattering can be considered with EXAFS), and in the multiple scattering regime, XANES. In EXAFS the photoelectron is scattered only by a single neighbour atom, in XANES all the scattering pathways, classified according to the number of scattering event (3), (4), (5) etc. contribute to the absorption cross section.
The XANES experiments done on plutonium in soil , concrete and standards of the different oxidation states .