  Structural, electronic and dielectric properties of high-quality ultrathin
BaTiO3 films are investigated. The films, which are grown by ozone-assisted
molecular beam epitaxy on Nb-doped SrTiO3 (001) substrates and having
thicknesses as thin 8 unit cells (3.2 nm), are unreconstructed and atomically
smooth with large crystalline terraces. A strain-driven transition to 3D island
formation is observed for films of of 13 unit cells thickness (5.2 nm). The
high structural quality of the surfaces, together with the dielectric
properties similar to bulk BaTiO3 and dominantly TiO2 surface termination, make
these films suitable templates for the synthesis of high-quality metal-oxide
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.
