NEXAFS

NEXAFS (Near‑Edge X‑ray Absorption Fine Structure) is a spectroscopic technique that probes the electronic structure of materials by measuring the absorption of X‑rays near the ionization edge of a specific element. When X‑ray photons with energies just above an element’s core‑level binding energy are absorbed, electrons are excited to unoccupied molecular or conduction‑band states. The resulting fine structure in the absorption spectrum, occurring within a few tens of electronvolts of the edge, reflects the density of these states and the local chemical environment.

The method is element‑specific because the core‑level energy is characteristic of each atom, allowing selective investigation of particular constituents in complex systems. Polarization dependence of the incident X‑ray beam provides information on the orientation of chemical bonds, making NEXAFS valuable for studying anisotropic materials such as thin films, polymers, and nanostructures. Compared with traditional X‑ray absorption spectroscopy, NEXAFS offers higher surface sensitivity when detected in electron yield mode, while fluorescence detection extends the probing depth for bulk analyses.

Applications span surface science, catalysis, energy storage, and organic electronics, where NEXAFS helps elucidate adsorption geometries, oxidation states, and electronic band alignment. Data are typically interpreted using ab‑initio calculations or reference spectra, facilitating quantitative assessments of bond hybridization and electronic structure. The technique is commonly implemented at synchrotron radiation facilities equipped with monochromators and suitable detection schemes.