Nucleation and growth of nanophasic CeO2 thin films by Plasma-Enhanced Chemical Vapor Deposition

Nanophasic CeO2-based thin films were grown at low temperatures on SiO2 and Si(100) by plasma-enhanced (PE) CVD from a Ce(IV) beta-diketonate first generation precursor. Film depositions were carried out in low-pressure Ar-O2 plasmas at temperatures between 150 and 300°C. The film microstructure was investigated by glancing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM), while their surface and in-depth chemical composition was studied by X-ray photoelectron spectroscopy (XPS) and by secondary ion mass spectrometry (SIMS) respectively. Optical properties were analyzed by UV-vis optical absorption. Nanostructured CeO2-based films, with crystal size less than 6 nm and a controllable Ce(IV)/Ce(III) ratio, were obtained at temperatures even lower than the one required for precursor vaporization (170°C). In particular, TEM analyses evidenced an island growth mode and different microstructural features as a function of the substrate used.