Influence of thickness on the epitaxial stabilisation of SmNiO 3 thin films

Abstract

SmNiO 3 thin films have been prepared by liquid injection Metal Organic Chemical Vapour Deposition on SrTiO 3 (100) and LaAlO 3 (100) single crystalline substrates. The influence of the film thickness on the epitaxial stabilisation has been studied for both substrates by X-ray diffraction and Atomic Force Microscopy (AFM). In the case of SmNiO 3 on LaAlO 3, the nickelate is obtained as a single phase up to a thickness of 200 nm; the surface remains smooth in agreement with the small lattice mismatch between film and substrate. In the case of the SrTiO 3 substrate, SmNiO 3 is never stabilised as single phase: NiO and Sm 2O 3 single oxides both appear beside the perovskite. We show that the strain state is driven by the choice of the substrate and the thickness of the film. Two different relaxation mechanisms of the film are evidenced depending on the substrate used. For LaAlO 3, the good in-plane lattice match leads to a relaxation only in the growth direction. On the contrary, in the case of SrTiO 3 which presents a strong lattice mismatch with the film, the out-of plane lattice parameter remains constant and constraints are relaxed through the chemical dissociation of SmNiO 3 into single oxides.