Growth dynamics and strain relaxation mechanisms in BaTiO3 pulsed laser deposited on SrRuO3/SrTiO3

The atomic structure of epitaxial BaTiO3 films grown on SrRuO3-covered (001)SrTiO3 substrates by pulsed laser deposition has been studied by transmission electron microscopy. It revealed a three-layered structure, each layer with a different morphology, remaining strain, and density of defects. These results pointed to the existence of two growth regimes with distinctive strain-relaxation mechanisms: (i) A first dislocation-free layer extending 3 nm from the coherent interface with SrRuO3. (ii) Beyond it, a second 7 nm thick semicoherent layer exhibiting a high density of misfit dislocations with a Burger vector a < 010 >. The structures of both layers are the outcome of a two-dimensional layer-by-layer growth regime. (iii) A third layer extending throughout the rest of the BaTiO3 film, showing a columnar structure of stoichiometric grains encapsulated by amorphous Ti-enriched boundaries, as disclosed by energy-dispersive x-ray spectroscopy. The structure of this third layer reflects its three-dimensional-featured growth habit. By considering both regimes as a single mode, the growth dynamics of the BaTiO3 films is discussed in relation to strain-relaxation mechanisms potentially responsible for the Stranski-Krastanov growth mode of this system.