Preparation of BiSrCaCuO thin films by atomic layer-by-layer molecular-beam-epitaxy and high-resolution transmission electron microscopy analysis of the film/substrate interface and of growth defects

By means of atomic layer-by-layer molecular-beam-epitaxy (MBE) we have prepared BiSrCaCuO thin films and vertical S-N-S (2212/2201/2212) junctions on SrTiO3 and LaAlO3 substrates at 720 degrees C in 2.10(-5) mbar ozone pressure. 40 nm thick Bi-2212 films show an inductively measured T-c of 84 K. The period of RHEED intensity oscillations, observed during growth, is correlated with the growth of half a unit cell. By means of HRTEM we have investigated the defect structure of the atomic layer-by-layer grown films. The films contain twins and interfacial dislocations. and some precipitates. Most prominent are Bi-rich precipitates of various size. interfacial dislocations were found to be located in the films at a distance of up to 3 nm from the film/substrate interface. The analysis showed that the film/substrate interface in the films is considerably sharper and has a better planarity, if the layer-by-layer MBE process starts with a Sr-O layer instead of a Bi-O layer.