Optical properties of CeO2 films prepared from colloidal suspension

Optical absorption of nanocrystalline thin films can be influenced by the p resence of both porosity and grain size effects. If both are present simult aneously, their effects are difficult to separate. In this study it is show n that the combination of uv-vis transmittance and reflectance measurements on porous CeO2 films provides enough data to make this separation. The CeO 2 films were prepared by deposition of nanosized (similar to5 nm) particles from a water colloidal suspension onto sapphire and subjecting these films to sintering temperatures sufficiently high to provide a series of films w ith a typical thickness of 0.6 mum with a wide range of grain sizes and por osity. X-ray diffraction, scanning electron microscopy, ellipsometry, and p rofilometry were used to characterize the films and to compare the observed grain sizes and porosity with that obtained from optical measurements. All of the techniques used gave results on porosity and grain size which were in good agreement, from 15% to 50% and 5 to 65 nm, respectively. For these porous films it was found that the changes in absorption which are normally explained by quantum confinement effects due to the small crystallite size can be attributed primarily to changes in porosity rather than in grain si ze. (C) 2001 American Institute of Physics.