Quantum confinement effect in high quality nanostructured CeO2 thin films

High quality crystalline nanostructured CeO(2) thin films were fabricated by pulsed laser deposition on R-cut sapphire substrates. As-grown and postannealed (in oxygen) films were investigated by atomic force microscopy, x-ray diffraction, and optical transmission and reflectance spectroscopy. The optical spectra changed as the microstructure varied from small grains to large quasi-two-dimensional islands. Hence, the band gap energy (E(g)) was found to increase systematically with the decrease in the grain size and ranged from 3.58 to 3.71 eV for the direct and from 3.01 to 3.26 eV for the indirect transitions. This is consistent with the quantum confinement model and, up to now, not observed in a convincing manner in the CeO(2) thin films. Results indicate that E(g) can be controlled in nanostructured thin films through thickness control and postannealing. (C) 2008 American Institute of Physics.