Unusual Peak Shifts in the Core Levels of CeO2 Films Deposited on Si(100)

Abstract

X-ray photoelectron spectroscopy has been used to study 20, 100 and 1000 nm evaporated cerium oxide films on Si(100) single-crystal wafers. Upon exposure to the x-ray source there was loss of oxygen and generation of Ce3+. Furthermore, for the 20 nm coating, there was evidence of a shift to higher binding energies of the C 1s peak and a high binding energy O 1s component relative to the oxygen anion peak at 529.7±0.1 eV with increased exposure time to the x-ray source. No similar shift was observed in the O KLL Auger lines, suggesting that the effect was not due to differential charging of the surface with respect to the bulk of the coating. Hence the relative shift is explained in terms of electronic effects resulting from the formation of anion vacancies in the surface. These include a shift of the Fermi level due to defect states in the bandgap as well as band bending due to the positive charge set up from the anion vacancies.