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X-ray Photoelectron Spectroscopy (XPS)

Photoelectrons result from the interaction of electromagnetic radiation with matter. Useful energy ranges for the exciting radiation go from UV (Ultraviolet Photoelectron Spectroscopy, UPS, leading to valence electrons excitation) to soft X-Rays (X-Ray Photoelectron Spectroscopy, XPS, leading to core level electrons excitation and hence to elemental selectivity). Excited photoelectrons are analyzed according to their kinetic energy, which is, at least for core electrons, a fingerprint of the emitting element.

Elemental identification is possible (except for H and He) for core level photoemission (5-1at%, the typical detection limit for most elements). Elements' relative abundance can be calculated in semi-quantitative or quantitative mode. Information on chemical bonds is derived either from core level shifts or from changes in the valence band electronic structure. Characteristic of the technique is its surface sensitivity (10 nm), which, combined with an etching process (usually through sputtering by accelerated noble ions) allows to measure elemental depth distributions.

Our laboratory features two XPS equipments: