Nanostructured Sapphire Vicinal Surfaces as Templates for The Growth of Self-Organized Oxide Nanostructures

Vicinal substrates of sapphire with miscut angle of 10° from the planes towards the direction have been annealed in air in the range from 1000 to 1500 °C. The behaviour of these surfaces has been characterized as a function of the temperature and the thermal treatment time by Atomic Force Microscopy observations. A thermal treatment at 1250 °C allows to stabilize a surface made of periodically spaced nanosized step-bunches. Such stepped surfaces were used as template to grow self-patterned epitaxial oxide nanoparticles by thermal annealing of yttria-stabilized zirconia thin films produced by sol–gel dip-coating. Grazing Incidence Small Angle X-ray Scattering and High-Resolution Transmission Electron Microscopy were used to study the morphology of the nanoparticles and their epitaxial relationships with the substrate.

Crystallization behaviors of sol—gel-derived LiNbO3 films, on sapphire and on MgO-doped LiNbO3 substrate, were observed by in situ TEM and high-resolution TEM. It was found that heterogeneous nucleation and growth of the crystalline LiNbO3 occurred with epitaxy on the interfaces between the films and the substrates, and the resulting epitaxial films were formed by coalescence of the crystallites. The difference in the crystallization behaviors, further, was observed between the films on the substrates. On MgO-doped LiNbO3 substrate which has small lattice mismatch with the film, the nucleation arose easily and the crystallites grew along the interface and towards a surface of the film. However, on sapphire substrate with the large lattice mismatch, the crystallites predominantly grew towards the surface of the film. The resulting film on sapphire substrate contained a large amount of structural defect at the grain boundary. The difference in the crystallization behaviors were discussed.


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