Microstructure of epitaxial Ba0.7Sr0.3TiO3∕SrRuO3 bilayer films on SrTiO3 substrates

Abstract

The thickness evolution of the microstructure of epitaxial ${\mathrm{Ba}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Ti}{\mathrm{O}}_3$ thin films grown on $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_3∕\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ was investigated by means of transmission electron microscopy. Within the ${\mathrm{Ba}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Ti}{\mathrm{O}}_3$ layer, a layered structure (three sublayers) is distinguished as for the configuration of lattice strain and defects. The first sublayer extends for $3\mathrm{nm}$ from the lattice-coherent ${\mathrm{Ba}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Ti}{\mathrm{O}}_3∕\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_3$ interface. The second $13\text{-}\mathrm{nm}$ -thick sublayer forms a semicoherent interface with the first sublayer due to the creation of a misfit dislocation network. The third sublayer extends beyond the second sublayer exhibiting a structure characterized by compact columnar features. Planar defects are formed at the boundaries between such features. The formation of a layered structure within the ${\mathrm{Ba}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Ti}{\mathrm{O}}_3$ films is discussed in the light of the growth modes of films on lattice-mismatched substrates.