Microstructure of strontium titanate thin film grown by the hydrothermal-electrochemical method

Microstructures of SrTiO₃ thin films grown on Ti substrates by the hydrothermal-electrochemical method have been studied by transmission electron microscopy. The grown films consisted of a thin surface layer having an isotropic polycrystalline structure and a thick inner layer having a columnar structure. Pores of the order of several tens of nanometers were found at boundaries of columnar grains constituting the inner layer. A 20- or 30-nm-thick polycrystalline layer of Ti oxides contaminated with a small amount of Sr was also found at the SrTiO₃ film/Ti substrate interface. During the film growth at this interface, the observed pores are considered to act as short-circuit paths for mass transport from the film surface to the interface.