Strain Relaxation in Buried SrRuO$_{3}$ Thin Film under a Biaxial Compression: CaZrO$_{3}$/SrRuO$_{3}$/SrTiO$_{3}$ System

We have observed a novel strain relaxation phenomenon in the buried thin film that develops during the deposition of an overcoat layer. In SrRuO$_{3}$/SrTiO$_{3}$ (100) system, the SrRuO$_{3}$ film is initially in biaxial compression, but the strain relaxation develops after a CaZrO$_{3}$ overcoat is deposited, manifested as misfit dislocations at the CaZrO$_{3}$/SrRuO$_{3}$ interface and a cross-hatch pattern of surface corrugation on the CaZrO$_{3}$ surface. This arises because CaZrO$_{3}$ (0.4012 nm) has a larger lattice parameter than those of SrRuO$_{3}$ (0.393 nm) and SrTiO$_{3}$ (0.3905 nm), thus contributing to the strain energy. By increasing point defect population in CaZrO$_{3}$ to accommodate the misfit strain, this phenomenon can be avoided and atomically flat thin film stacks obtained.