Epitaxial growth and dielectric properties of BaTiO3 films on Pt electrodes by reactive evaporation

Abstract

Thin films of BaTiO₃ have been epitaxially grown on Pt(001)/MgO(100) substrates by reactive evaporation. Structural and electrical properties were investigated as a function of film thickness. In situ reflection high‐energy electron diffraction and cross‐sectional transmission electron microscope observations have revealed that the BaTiO₃ films are epitaxially grown on Pt/MgO substrates from the initial stage without any other phase formation. From the images of an atomic force microscope, it has been found that islands of BaTiO₃ are present on the bare Pt surface at the initial stage of deposition; the island structure changes to a continuous layer above 1.2 nm in thickness and BaTiO₃ grows in a two‐dimensional mode. The lattice parameters and the dielectric properties are dependent on the film thickness. Thermodynamic theory was introduced to explain the thickness dependence of the relative dielectric constant ε_r. Good agreement between the experimental results and the theoretical calculations leads to the conclusion that the thickness dependencies of the lattice parameters and the dielectric constants are caused by the two‐dimensional stress due to the lattice mismatch between Pt and BaTiO₃ and/or the difference in the thermal expansion coefficients of BaTiO₃ and the MgO substrate.