Transmission electron microscopy study on epitaxial growth behaviors of sol-gel-derived LiNbO3 films

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.