Effects of crystal quality, grain-size and oxygen vacancy of nanocrystalline CeO2 films under 1.5 MeV Au ion irradiation

Abstract

Nanocrystalline CeO2 films with thickness of approximate 250 nm were grown on Si substrates using a sol-gel process with spin-coating method. The films were then irradiated with 1.5 MeV Au ions to the doses of 2.5, 15.0 and 35.0 dpa at room temperature. Electron microscope results show that the surface of the as-grown CeO2 film is very smooth, and no any cracks are detected. The as-grown CeO2 film is cubic fluorite structure with an average grain-size of 6.4 nm. The nanocrystalline CeO2 films remain cubic structure under all irradiation conditions. The crystallinity and average grain-size of the CeO2 film decrease with the increase of irradiation dose, which is due to the competing effects of electronic and nuclear energy loss. As the irradiation dose is up to 35.0 dpa, the crystal quality is obviously deteriorated as well as the surface microstructure. Raman spectra also confine that the grain-size of the nanocrystalline CeO2 films decreases with the irradiation dose increase. X-ray photoelectron spectroscopy (XPS) results reveal that parts of Ce4+ in the nanocrystalline CeO2 films change to Ce3+, and oxygen vacancy concentration also increases after irradiation. All these samples exhibit two emission bands in the photoluminescence (PL) spectra, and the relative emission intensity of the defect peak centered at 500 nm is enhanced by ion irradiation, which also indicates that irradiation introduces oxygen vacancies into the nanocrystalline CeO2 films. This work provides a useful way to control the grain-size and oxygen vacancy of the nanocrystalline CeO2 films through ion implantation technique.