A photoemission study of the ceria and Au-doped ceria/Cu(111) interfaces

The photoelectron spectroscopy (PES) study compares electronic states in three different ceria thin film surfaces prepared on a Cu(111) single-crystal surface by vapour deposition under different conditions: at 250 °C, at room temperature and finally Au-doped ceria film obtained by simultaneous deposition of Au and CeO₂ at room temperature (RT). Electronic properties of the layers and interaction of gold with CeO₂ were investigated using synchrotron-radiation-excited PES and resonant photoemission (Ce 4d → 4f transitions). We observed partial Ce⁴⁺ → Ce³⁺ reduction induced by the decrease of deposition temperature to RT instead of 250 °C and also by doping ceria with gold, accompanied by a 4f resonance enhancement of the Ce³⁺ species. In the case of the Au-doped sample the surface reduction degree is stronger and can be explained by the possible creation of a new ionic Au⁺ state observed in the Au 4f spectra.