MICROSTRUCTURAL EVOLUTION AND EPITAXIAL ALIGNMENT OF THIN-FILMS OF LITHIUM-NIOBATE DEPOSITED ONTO SAPPHIRE BY METALLOORGANIC DECOMPOSITION

LiNbO3 films were prepared by spin coating and thermal decomposition o f a solution of metallo-organic precursors on single-crystal [0001] or iented Al2O3 substrates, followed by heat treatment in a quartz tube f urnace at temperatures ranging from 500 to 1000 degrees C. X-ray diffr action and ion-channeling analyses reveal that the LiNbO3 grows epitax ially aligned with respect to the Al2O3 substrate. The degree of epita xial alignment depends on the heat treatment temperature, with the bes t films obtained on heat treatment at 900 degrees C for 30 min to 1 h. The morphology of the films appears to depend on the kinetics of the decomposition process. Films pyrolyzed by slow heating from room tempe rature to about 500 degrees C, and subsequently heat treated at higher temperatures, tend to be non-uniform, breaking into a network of grai ns and partially uncovering the substrate. Interestingly, pole-figure analysis shows that all the grains share the same in-plane as well as out-of-plane epitaxial orientation. Films prepared by rapid thermal de composition of the precursor solution at 500 degrees C. followed by he at treatment at 900 degrees C, are continuous, smooth, and epitaxially aligned.