Electron energy loss spectroscopy investigation of Pb and Ti hybridization with O at the PbTiO3/SrTiO3 interface

Studies of oxide interfaces, and how they affect physical properties, have recently gained large attention. For ferroelectric materials, the evolution of the order parameter close to an interface is important to understand regarding the stability of the ferroelectric phase, and how to optimize devices taking advantage of the polarization at the interface. Here we employ electron energy loss spectroscopy (EELS) in scanning transmission electron microscopy to compare the electronic and structural properties in both bulk and interface regions of epitaxial PbTiO3 thin films grown on SrTiO3 substrates. At the interface, changes in EELS spectra of the Ti-L-3,L-2 and O-K edges, as compared to the bulk of the thin film, reveal a reduction in the hybridization of Ti 3d and Pb 6sp states with O 2p, and thus tetragonal distortion of the TiO6 octahedron. Real-space multiple-scattering calculations of the O-K edge support the experimental results. Moreover, the analysis of the Ti-valence reveals that the change is gradual over similar to 2-3 nm. The data implies a decreasing ferroelectric order parameter over similar to 2-3 nm close to the PbTiO3 SrTiO3 interface with a nonzero value at the interface with an additional screening of the polarization over similar to 1-2 nm into the SrTiO3 substrate from the Ti atoms. (C) 2011 American Institute of Physics. doi:10.1063/1.3544416]