X-ray absorption spectroscopy

X-ray absorption spectroscopy measures a material’s X-ray absorption as photon energy varies, revealing the local electronic structure and atomic environment around selected elements.

X-ray absorption near-edge structure: The near-edge portion of an X-ray absorption spectrum, sensitive to oxidation state, symmetry, and unoccupied electronic states. Its edge position and shape provide chemical-state information within the measured spectrum.
X-ray absorption spectroscopy of catalysts: The use of X-ray absorption spectra to probe catalyst composition and local structure during preparation or reaction. Catalysts can be studied under working conditions even when their active sites lack long-range order.
Core electron: An electron occupying an inner atomic shell, tightly bound to the nucleus compared with valence electrons. The absorption process begins by exciting a core electron into an unoccupied state or continuum.
X-ray diffraction: A method that infers ordered structure from the angles and intensities of X-rays scattered by a material. Unlike diffraction, absorption spectroscopy can probe local order without crystallinity.
Extended X-ray absorption fine structure: Oscillations beyond an absorption edge caused by interference between an excited photoelectron and waves scattered by neighboring atoms. Its oscillations reveal distances and coordination around the absorbing atom.
Operando spectroscopy: Spectroscopic measurement of a material while it performs its intended function under relevant operating conditions. X-ray absorption can track changing catalyst states during reaction.
Photoelectron: An electron emitted from a material after absorbing a photon with sufficient energy. Its scattering from nearby atoms generates the oscillatory fine structure.
X-ray photoelectron spectroscopy: A surface-sensitive technique that measures the kinetic energies of electrons emitted by X-ray irradiation. It analyzes emitted electrons, whereas absorption spectroscopy measures incident-beam attenuation.
X-ray absorption edge: The sharp rise in X-ray absorption that occurs when photon energy can eject a core electron from an atom. The edge identifies the absorbing element and often shifts with its chemical state.
X-ray absorption spectroscopy in biology: The use of element-specific X-ray absorption measurements to study metal centers in biological molecules and systems. It probes metal coordination in enzymes without requiring crystalline samples.

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