Variable angle spectroscopic ellipsometry (VASE) has been used in the photon energy range 1.25–5.0 eV to study the structure and optical properties of cerium dioxide (CeO2) films. Both amorphous and highly oriented crystalline films were grown on sapphire by rf magnetron sputtering. The crystallinity, chemical structure, and surface morphology of the films were studied by x-ray diffraction, x-ray photoelectron spectroscopy, and atomic force microscopy, respectively. The measured VASE spectra on a series of films with different thicknesses were analyzed by using multiple optical models. In this way, the complex refractive index N=n+ik of CeO2, the film thicknesses, and the surface roughness of the different films could be determined. The ellipsometrically deduced refractive index spectrum was observed to be strongly dependent on the film structure. Highly oriented crystalline CeO2 films exhibited a higher refractive index and a higher band gap energy than the amorphous film. The surface roughness of the crystalline films increased with film thickness. The optical dispersion relations have also been analyzed by line-shape fitting with a modified Lorentz oscillator model.

No abstract

CeO2 films with thicknesses ranging from 8.8 to 199 nm were grown on Al2O3 (1102) (R-cut) substrates by off-axis rf magnetron sputtering. X-ray diffraction showed an epitaxial relationship with the CeO2 (001) planes parallel to the Al2O3 (1102) planes for all film thicknesses. Atomic force microscopy (AFM) revealed a rough surface morphology consisting of crystallites with lateral dimensions of 10–90 nm. In the thinnest film, these crystallites were regularly shaped and uniformly distributed on the substrate, while they were rectangularly shaped and oriented mainly in two directions, orthogonal to each other, in the thicker films. The surface roughness of the films increased with increasing layer thickness. Characterization of the microstructure was done by cross-sectional transmission electron microscopy (XTEM) and showed a polycrystalline, highly oriented, columnar structure with a top layer terminated by (111)-facets. High-quality YBa2Cu3O7−δ (YBCO) thin films were deposited directly onto the CeO2 layers. XTEM, rather surprisingly, showed a smooth interface between the YBCO and CeO2 layer. Postdeposition ex situ annealing was carried out on two CeO2 films and evaluated by AFM. Upon annealing samples at 930 °C, a relatively smooth morphology without facets was obtained. Annealing films at 800 °C caused no appreciable change in surface morphology, whereas igniting a YBCO plasma during a similar anneal clearly altered the sample surface, giving facets that were rounded.

No abstract

Sr-deficient and stoichiometric epitaxial (001) SrTiO3 films, deposited on (110)rhombohedral LaAlO3 substrates by rf magnetron sputtering, have been characterized using high-resolution transmission electron microscopy. A subsequent heat treatment in oxygen had a positive influence on the dielectric properties. Sr-deficiency had a large negative impact on the microwave dielectric constant of the films. These changes were correlated to changes in lattice parameters. In all samples, at the film/substrate interface, were misfit dislocations present. The residual elastic strain compressed the SrTiO3 unit cell in the substrate surface plane and expanded it an equal amount in the [001] direction. X-ray diffraction revealed that the tetragonal distortion, due to the mismatch strain, was concentrated to a narrow region closest to the film/substrate interface.