Microstructure of electron-beam-evaporated epitaxial yttria-stabilized zirconia/CeO₂ bilayers on biaxially textured Ni tape

Transmission and scanning electron microscopy, atomic force microscopy, X-ray pole figure analysis and Auger electron spectroscopy were used to characterize the micro structure and surface topography of epitaxial yttria-stabilized zirconia (YSZ) and CeO₂ thin films deposited by electron beam evaporation on rolling-assisted biaxially textured Ni substrates (RABiTS™). The as-deposited YSZ layer is composed of highly crystallographically aligned, slab-shaped columnar grains with sharply defined, rectangular cross sections and average dimensions of 10 nm by 50 nm by the film thickness. The faces of the YSZ slabs lie on the {110} planes that contain the surface normal. Their caps are roof-shaped with a peak-to-valley height of about 10 nm and a RMS roughness, measured by atomic force microscopy, of 1.3 nm. The resultant surface morphology is rough, but shows a regular, cross-hatched pattern on the length scale of about 10 nm. The length scale and crystallographic directionality of the YSZ micro structure is retained when YBa₂Cu₃O_7-δ is pulsed laser deposited on it, but the YSZ columns appear to have sintered into a less angular, more distinctly porous microstructure. The CeO₂ layer also is columnar, but appears to be denser, with a flatter, less directional surface topography. Auger sputtering-depth profiling experiments revealed that the compositions of both films are constant through the film thickness and that interdiffusion along the surface normal is not extensive.