Radiation-Induced Reduction of Ceria in Single and Polycrystalline Thin Films

The effect of radiation on the oxidation state of Ce in high-quality single and polycrystalline ceria thin films is presented. The films were synthesized by molecular beam epitaxy and irradiated with high energy ionizing radiation of 2 MeV He+ ions with varying flux density. The surface chemistry of the irradiated ceria thin films was characterized by in situ X-ray photoelectron spectroscopy (XPS). Upon irradiation, the concentration of Ce3+ increased by 13 and 19% in single and polycrystalline ceria, respectively. Molecular dynamics simulation of thermal spikes and displacement cascade damage provide details of radiation induced defects at the end of the range of the ions that can contribute to the observed reduction.