Specific mechanism for strain relaxation dependent on crystallization route of LiNbO3 films on Al2O3(0001)

Abstract

Distinct channels for relaxing strain were identified in epitaxial LiNbO3 thin films depending on whether the film was crystallized during or after sputter-deposition on an Al2O3(0001) substrate. When LiNbO3 continuously crystallizes during deposition, pseudomorphic growth continues with a build up of strain as the thickness increases. The primary process for relieving strain is achieved by dividing the crystal into small mosaic grains. Crystallization by postannealing amorphous films, in contrast, produces nearly dislocation-free, relaxed crystals with a wider domain of 100–200 nm. Introducing lattice disorder at antiphase positions that correspond to matching between 12 lattice units of LiNbO3 and 13 lattice units of Al2O3 in the a-direction limits the chemical interaction with the Al2O3 lattice within a short range and efficiently accommodates misfit strain. This results in atomic-scale grapho-epitaxy sustaining disordered lattice regions at the interface.