HREM OBSERVATIONS OF (SR, CA)CUO2 INFINITE-LAYER THIN-FILM PREPARED BY RF THERMAL PLASMA EVAPORATION

(Sr, Ca)CuO2 infinite-layer thin films prepared by RF thermal plasma evaporation are investigated by high-resolution electron microscopy. Perfect infinite-layer thin films with the lattice parameter c ranging from 3.3 to 3.4 angstrom are found epitaxially grown on SrTiO3 substrate before plasma annealing. Only one type of planar defect due to double SrO layers is found perpendicular to the substrate surface in all films. The doping of Na is found to cause planar defects parallel to the substrate surface with average spacing about 8 times the c parameter in the c direction in which the density of planar defects is related to the doping content of Na. After plasma annealing below 300-degrees-C, the infinite-layer structure of the film is found to change into a 2 square-root 2a(p) X 2 square-root 2a(p) X c structure, where a(p) = 3.90 angstrom and c = 3.6 angstrom. The diffraction conditions combined with analysis of the sample preparation process suggest the partial appearance of apical oxygen in the Sr layer in the film with the superstructure.