Re-orientation of graphoepitaxial fluorite films towards small-index crystallographic planes

Graphoepitaxial CeO₂ and Y:ZrO₂ (YSZ) thin films showed re-orientation towards (012), (013) small-index crystallographic planes (SIPCs) due to surface energy minimization effects, with deviation from the expected tilt angles up to 4.5º. Re-orientation of the CeO₂ films towards the (012) plane was obtained for the intermediate range of deposition rate and oxygen partial pressure, providing high plasticity of the lattice of the film due to formation of oxygen vacancies, and the relatively low bonding strength of the film-substrate interface. The realization of re-orientation of the YSZ graphoepitaxial films demanded intentional suppression of the epitaxial bonding between the film and the substrate. The effect was observed both for (012) and (013) SICPs. The re-orientation is obtained easier when the film experiences additional tilting towards the substrate plane, reaching inclination angles of 2.5-4.5º. The re-orientation from the substrate plane is also possible, but such films are usually re-oriented partially, and the observed inclination angle is limited to ~0.3º. The re-oriented films show a lower spread of orientations of domains, observed as a decrease of the width of the rocking curve. The reason is the co-orienting effect of the substrate surface during growth, opposite to the mis-orienting effect of dislocations generation for ordinary graphoepitaxial films. The lattice constant normal to the epiplane experiences distortion near the surface of the film, contractive for a decrease of the final tilt angle and tensile for re-orientation from the substrate surface.