Probing the Electronic Structures of BaTiO3/SrTiO3 Multilayered Film with Spatially Resolved Electron Energy-Loss Spectroscopy

A multilayered film of BaTiO 3 /SrTiO 3 was grown on a LaAlO 3 substrate using dual-target pulsed laser deposition technique. High-resolution scanning transmission electron microscopy observations show that the nine unit-cell BaTiO 3 layer and the three unit-cell SrTiO 3 layer are alternatively arranged in the epitaxial film where a sharp interface exists between the BaTiO 3 and SrTiO 3 layers. Electron energy-loss spectroscopy analysis demonstrates that the O- K edge spectra of SrTiO 3 and BaTiO 3 layers are quite distinct; in particular, the energy-loss peak at 547 eV in the SrTiO 3 spectrum splits into two peaks in the BaTiO 3 spectrum. The multiple-scattering calculations of O- K edge spectra for BaTiO 3 and SrTiO 3 agree well with the experimental results. The low-energy region (<542 eV) of the O- K edge spectra for both BaTiO 3 and SrTiO 3 is mainly caused by the hybridization of the O 2p with Ti 3d orbitals. The splitting peaks between 542 and 552 eV in the O- K edge spectra of BaTiO 3 are attributed to its complex crystal structure including two unequal oxygen sites and low site symmetry.