Growth of ultrathin BaTiO3 films on SrTiO3 and MgO substrates

Epitaxial BaTiO3 thin films were successfully grown on SrTiO3 (001) and MgO (001) substrates by molecular beam epitaxy. These 50 ML thickness BaTiO3 films were prepared under the same growth conditions on both substrates. The films were characterized by in situ reflection high-energy-electron diffraction observations and ex situ X-ray diffraction measurements. The epitaxial relationship between the BaTiO3 films and both substrates was cube-on-cube, though the cubic lattice parameter of BaTiO3 was larger than that of SrTiO3, and smaller than that of MgO at the growth temperature (700 degrees C). In addition, the films on both substrates were found to have a highly c-axis-oriented tetragonal phase at room temperature. However, despite the finding that the lattice parameters of these films were very close to the bulk value of the tetragonal phase, the crystal quality as found to depend strongly on the magnitude of the lattice mismatch. (C) 1998 Elsevier Science B.V. All rights reserved.