Ultrathin BaTiO₃ templates for multiferroic nanostructures

The structural, electronic and dielectric properties of high-quality ultrathin BaTiO₃ films were investigated. The films, which were grown by ozone-assisted molecular beam epitaxy on Nb-doped SrTiO₃ (001) substrates and have thicknesses as low as 8 unit cells (u.c.) (3.2 nm), are unreconstructed and atomically smooth with large crystalline terraces. A strain-driven transition to three-dimensional (3D) island formation is observed for films of 13 u.c. thickness (5.2 nm). The high structural quality of the surfaces, together with dielectric properties similar to bulk BaTiO₃ and dominantly TiO₂ surface termination, makes these films suitable templates for the synthesis of high-quality metaloxide multiferroic heterostructures for the fundamental study and exploitation of magneto-electric effects, such as a recently proposed interface effect in Fe/BaTiO₃ heterostructures based on Fe-Ti interface bonds.