Microstructures of La1−xAx(A = Ca or Sr)MnO3−δthin films by liquid-delivery metalorganic chemical vapor deposition

Abstract

The microstructure of La1–xAx(A = Ca or Sr)MnO3–δthin films grown by liquid-delivery metalorganic chemical vapor deposition on (001) MgO and (110)pseudo-cubicLaAlO3were studied by transmission electron microscopy. The La1–xCaxMnO3–δthin film on large lattice mismatched MgO exhibited very defective microstructures and consisted of two typical regions. The first region was close to the film–substrate interface and had an epitaxial relationship to the substrate with many differently oriented domains nucleated on the substrate surface. The second region consisted of columnar grains with some degree of texture. In contrast, the smaller lattice-mismatched La1–xSrxMnO3–δ/(110)pseudo-cubicLaAlO3film had good crystalline quality with highly oriented columnar grains but exhibited complicated dislocation structures. Apart from the misfit dislocations formed at the film–substrate interface, two types of anomalous dislocations with limited contribution to relieving misfit stresses were also observed. One type of dislocation had extra planes in the film and some climbed into the substrate. These dislocations were considered to form from dislocation loops during nucleation of the film. The other type of dislocations had extra planes parallel to the film–substrate interface and glided into the substrate side resulting in a 2° tilt of the film with respect to the substrate. The complicated dislocation configurations present in the sample were related to the complex strain field in the film. The relative strains along the interface measured in the film were heterogeneous. The variations of the strains in the film were related to the local Curie temperature changes and second-order phase transitions of the film.