Aberration-corrected HRTEM of defects in strained La2CuO4 thin films grown on SrTiO3

The structure of lattice defects in thin La2CuO4 films grown under tensile strain on SrTiO3 (001) is investigated by the combination of state-of-the-art medium voltage aberration-corrected transmission electron microscopy together with numerical exit-plane wavefunction reconstruction. The interfacial reconstruction, the coordination in planar shear defects evolving from surface steps and misfit dislocations of the b = a[010] type are atomically resolved and analysed. Quantitative mapping and evaluation of peak data related to cation atom columns reveal the formation of a perovskite-like layer of lanthanum copper oxide analogous to the thermodynamically instable LaCuO3-delta phase and a distortion in the octahedral coordination of copper at the interface to the substrate. The planar shear defects embody extra sites for cations and oxygen in a three-dimensional periodic arrangement which are partially filled and provide paths for vacancy hopping transport. The central structure of the misfit dislocation does not exhibit mirror symmetry around a plane containing the dislocation line owing to the asymmetric arrangement of cation columns.