Comparative studies of nanostructural and morphological evolution ofCeO2 thin films induced by high-temperature annealing

Abstract

High-temperature annealing performed at∼1000 °C orhigher in an oxidizing atmosphere is a simple technique to significantly modify the as-grown nanostructuresof CeO2 films, which are typically granular with high surface roughness.We evaluated the effect of high-temperature annealing on variousCeO2 films deposited by three deposition methods, namely standard pulsed laser deposition (PLD),large-area pulsed laser deposition, and electron-beam evaporation. High-temperature annealingpromotes high epitaxy and crystallinity, as well as stabilization of the flat (001) surfaces ofCeO2. This is most commonly observed on the annealedCeO2 film grown by standard PLD, which is usually atomically smooth and pore-free. In contrast,CeO2 films grown by large-area PLD and electron-beam evaporation are characterized bysimilarly flat surfaces but are discontinuous due to the presence of pores. Depending on thelength of the annealing time, the pores range from small-sized nanopores with widths of∼30–100 nm anddepths of ∼3–5 nm, up to relatively large-sized pores with widths of∼100–500 nm anddepths of ∼10–20 nm. The differences in the nanostructural and morphological evolution of theCeO2 films are further correlated to their as-grown properties, including grain size, orientation,and possibly the initial porosity of the film.