The electronic structure of stoichiometric and reduced CeO2 surfaces: an XPS, UPS and HREELS study

The influence of Ce3+-related defects on the electronic structure of stoichiometric CeO2 surfaces is studied by means of detection angle-dependent XPS, UPS and HREELS. Argon sputtering and hydrogen exposure at elevated temperatures lead to high concentrations of Ce3+ at surface and subsurface sites. The latter are identified by the binding energies of the Ce 3d core levels, additional emissions of C4f1-derived electronic states in the band gap, and characteristic changes in the electronic transitions from occupied into empty electronic states in the valence band region. UPS is found to show in particular a high sensitivity for intrinsic surface point defects, even if small concentrations are adjusted in the order of XPS and HREELS detection limits by high-temperature treatment of the CeO2 surfaces under UHV conditions or by hydrogen exposure at medium temperatures