Morphology and microstructure of (111) crystalline CeO₂ films grown on amorphous SiO₂ substrates by pulsed-laser ablation

The surface morphology and microstructure of (111)-oriented CeO₂ thin films, grown on amorphous fused silica (SiO₂) substrates by low-energy-ion-beam assisted pulsed laser ablation, have been studied by atomic force microscopy (AFM) and x-ray diffraction (XRD). These CeO₂ films are aligned with respect to a single in-plane axis despite being deposited on an amorphous substrate. There is a honeycomb-like growth morphology to the films and island-growth can be observed in thicker films. These islands, inside of which are high density of honeycomb-like clusters, are separated by a void network with approx.700nm width. However, on the surface of the thinnest film (approx.3nm), only very small clusters (diameter <60nm) appear, and the boundaries of the void network are undefined, which implies that the film is just beginning to coalesce into clusters (grains). The combined AFM images and XRD pattern suggest these clusters probably are the initial seeds for the subsequent island growth. Based on these results, the growth mechanism of oriented CeO₂ films on amorphous fused silica substrates is discussed.