Polar distortion in ultrathin BaTiO3 films studied by in situ LEED I-V

Phase stability in nanoscale ferroelectrics is governed by the interplay of electrostatic depolarization energy, domain formation, adsorption, and surface band bending. Using in situ low-energy electron-diffraction intensity versus voltage (LEED I-V), we have characterized 4 and 10 ML BaTiO3 films, grown using pulsed laser deposition with fully compressive strain on a SrRuO3/SrTiO3 substrate. LEED I-V reveals a single surface dead layer and a monodomain vertically polarized state below. The single orientation is attributed to the intrinsic imprint asymmetry and the stability of a polarized phase to compensation of depolarizing charges by dipoles induced by surface stress.