Photoelectron Spectroscopy Study of Oxidation of Ce Films

Photoelectron spectroscopy has been used to study oxidation of Ce films at room temperature.The Ce oxidation state and work function changes were investigated at different oxygen exposures.The results show that there exist two kinds of Ce oxides during oxgyen adsorption.At low exposures,a fast oxgyen adsorption on Ce surface is related to the formation of Ce₂O₃ and the Ce3d and O1s core levels shift to lower binding energy with increasing oxygen exposure.At high exposures,a slow oxygen adsorption is due to the oxidation of Ce₂O₃ on the top layer,forming CeO 2.The dioxide can be converted into sesquioxide again by annealing.Work function change displays an initial decrease at low exposure,followed by an increase.