Relationship between the nanostructures and the optical properties of CeO2 thin films

CeO2 nanostructured thin films have been deposited on Al2O3(1-102) and TiO2(001) single-crystal substrates through metal-organic chemical vapor deposition (MOCVD) using the Ce(III) 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato diglyme adduct (Ce(hfa)(3).diglyme). Structural and morphological characterizations have been carried out by X-ray diffraction pattern (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) measurements. It has been found that the deposition temperature and the lattice mismatch with the substrate have a strong impact on the film nanostructure. X-ray diffraction patterns of samples grown at low deposition temperature point to the formation of <100> oriented CeO2 films, while films deposited at higher deposition temperatures have <111> texture. Furthermore, SEM cross section images clearly point to relevant effects of deposition temperatures both on the structural alignment of CeO2 grains as well as on the film/substrate interfaces. Spectroscopic ellipsometric measurements provide a suitable rationalization of correlations between nanostructures and optical properties of the CeO2 films. Moreover, combination of SEM and spectroscopic ellipsometric measurements provide an in-depth interpretation of growth modes.