X-ray Photoelectron Spectroscopy gives elemental and compositional information from the top few surface atomic layers. Incident soft X-rays induce photoelectron emission from the sample, and kinetic energy analysis of the electrons emitted without experiencing energy losses enables identification of the atom and orbital of origin. Information on bonding, oxidation states and chemical environments is derived from small “chemical” shifts in the binding energies of these electrons. Sampling depth is characterised by an exponential decay length of typically a few monolayers. Surface sensitivity can be further enhanced by use of shallow take-off angles, and depth profiling can be carried out using ion sputtering.

Auger electron spectroscopy (AES) is also available if small-area (e.g. down to ca. 1 micron area) surface analysis is required.