HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY STUDY OF INTERFACE STRUCTURES AND GROWTH DEFECTS IN EPITAXIAL BI2SR2CAN-1CUNO4+2N+DELTA FILMS ON SRTIO3 AND LAALO3

The defect structure of epitaxial, c-oriented Bi2Sr2Can-1CunO4+2n+delt a (BSCCO) thin films grown by dc-sputtering and layer-by-layer MBE on SrTiO3 and LaAlO3 single crystal substrates was investigated by high-r esolution transmission electron microscopy (HRTEM). Particular emphasi s was put on the structure of the film/substrate interface. The films grown by dc-sputtering show a rather perfect structure involving a reg ular stacking of the unit cells. In spite of this regularity, there ar e many defects, such as twins, chemical stacking faults, and precipita tes, as well as interfacial dislocations accommodating the film/substr ate lattice misfit. The MBE-grown films contain twins and interfacial dislocations, but most prominent are precipitates of various size and rather high number density. Composition and structure of the precipita tes were analyzed. Interfacial dislocations were found to be located i n the films at a distance of up to 3 nm from the film/substrate interf ace. The experiments showed that the quality of the film/substrate int erface in MBE-grown films is considerably higher with respect to smoot hness, sharpness, and regularity, if the layer-by-layer MBE process st arts with a Sr-O layer instead of a Bi-O layer. This observation is in correspondence to the observed interface structure of the dc-sputtere d films, where the first film layer was a Sr-O layer, not a Bi-O layer , in spite of the films being sputtered from a composite target, A str ucture model of the Bi2Sr2Can-1CunO4+2n+delta/(100)SrTiO3 interface is proposed. The prolonged MBE process was shown to imply a chemical int eraction between the SrTiO3 substrate and the growing film, resulting in the formation of Sr-rich phases in the near-interface substrate reg ions.