Microstructure of strained La2CuO4+δ thin films on varied substrates

Layered perovskite La2CuO4+δ (LCO) thin films were epitaxially grown on SrTiO3 (STO) and LaSrAlO4 (LSAO) substrates by atomic-layer-by-layer molecular beam epitaxy. The lattice de- fects and residual strain in these films were investigated by means of transmission electron mi- croscopy and electron energy loss spectroscopy. The LCO films showed a high epitaxial quality with flat interfaces and top surfaces. Misfit dislocations with Burgers vector a<010> and shear defects were frequently observed at or near the film/substrate interfaces and in the films, respec- tively, for all the LCO films. In one LCO film, grown on STO at the highest temperature, 700 oC, was a two layered structure. The top layer was identified as rhombohedral LaCuO2 by electron energy loss spectroscopy combined with electron diffraction. In addition, stacking faults were observed in plane-view micrographs of one LCO film grown on the STO substrate. The residual strains were evaluated from the spacing of misfit dislocations at the film/substrate interface and