title: Studies of local structural distortions in strained ultrathin BaTiO3 films using scanning transmission electron microscopy.
abstract: Ultrathin ferroelectric heterostructures (SrTiO3/BaTiO3/BaRuO3/SrRuO3) were studied by scanning transmission electron microscopy (STEM) in terms of structural distortions and atomic displacements. The TiO2-termination at the top interface of the BaTiO3 layer was changed into a BaO-termination by adding an additional BaRuO3 layer. High-angle annular dark-field (HAADF) imaging by aberration-corrected STEM revealed that an artificially introduced BaO-termination can be achieved by this interface engineering. By using fast sequential imaging and frame-by-frame drift correction, the effect of the specimen drift was significantly reduced and the signal-to-noise ratio of the HAADF images was improved. Thus, a quantitative analysis of the HAADF images was feasible, and an in-plane and out-of-plane lattice spacing of the BaTiO3 layer of 3.90 and 4.22 Å were determined. A 25 pm shift of the Ti columns from the center of the unit cell of BaTiO3 along the c-axis was observed. By spatially resolved electron energy-loss spectroscopy studies, a reduction of the crystal field splitting (CFS, ΔL3=1.93 eV) and an asymmetric broadening of the eg peak were observed in the BaTiO3 film. These results verify the presence of a ferroelectric polarization in the ultrathin BaTiO3 film.
authors.forename: Daesung
authors.initials: D
authors.lastname: Park
authors.forename: Anja
authors.initials: A
authors.lastname: Herpers
authors.forename: Tobias
authors.initials: T
authors.lastname: Menke
authors.forename: Markus
authors.initials: M
authors.lastname: Heidelmann
authors.forename: Lothar
authors.initials: L
authors.lastname: Houben
authors.forename: Regina
authors.initials: R
authors.lastname: Dittmann
authors.forename: Joachim
authors.initials: J
authors.lastname: Mayer