Microstructure and residual strain in La2CuO4 thin films on LaSrAlO4-buffered SrTiO3 substrates -: art. no. 075416

The microstructure and residual strain of bilayer films of La2CuO4/LaSrAlO4 on SrTiO3 substrates are investigated by means of electron-diffraction analysis and high-resolution transmission electron microscopy. In two samples containing LaSrAlO4 buffer layers with thicknesses of 37 and 75 nm, a compressive strain is measured in the La2CuO4 layers. From the presence of lattice defects close to interface imperfections it can be concluded that the thickness of these La2CuO4 layers is close to the critical value for mismatch-strain relaxation. The strain level in the layer on the 37-nm-thick buffer is lower than that in the layer on the 75-nm buffer. A high density of planar shear defects is observed which can be introduced by steps of the substrate surface and by stacking faults in the film. Interfacial stacking faults are found at the interface between the La2CuO4 and the LaSrAlO4 layers. Interface roughening can hinder the formation of these faults. In addition, a strong roughness of the interface is found to induce strong lattice bending and extra strain in the La2CuO4 layer.