X-RAY-INDUCED REDUCTION EFFECTS AT CEO2 SURFACES - AN X-RAY PHOTOELECTRON-SPECTROSCOPY STUDY

XPS techniques are used to study the effects of Al K-alpha x-rays on the surface chemical composition of CeO2. We find that prolonged exposures cause the formation of some Ce3+ oxidic species at the surface. We have studied the Ce 3p, Ce 3d, O 1s, Ce 4p, Ce 4d, and valence band regions in an attempt to localize the depth of damage. Consideration of published formulations for electron attenuation lengths and electron inelastic mean free paths indicates that the chemical reduction occurs mainly in the first 15-20 angstrom from the surface. Our results show that some of the XPS features, usually referred to as excited electronic states of ceria, are in fact induced by prolonged exposures to the x rays.