SURFACE-TOPOGRAPHY AND BULK STRUCTURE OF BI2SR2CACU2O8-TUNNELING-MICROSCOPY AND HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY(DELTA FILMS OBSERVED BY SCANNING)

The surface topography of thin Bi2Sr2CaCu2O8+delta films prepared on S rTiO3 (001) substrates by DC sputtering and layer-by-layer molecular-b eam epitaxy (MBE) growth was investigated by scanning tunneling micros copy. The films were smooth but displayed a number of fine-scaled surf ace features, among them steps of unexpected height and domains of the incommensurate lattice modulation. The modulation period varied in de pendence on the oxygen content of the films. High-resolution transmiss ion electron microscopy investigations of cross sections were undertak en in order to identify the origin of the surface features and to corr elate them with the bulk structure of the films. The surface steps on the DC sputtered films were shown to originate from the interplay of t he island growth mode with nanometer-scale fluctuations of the chemica l composition. The domains of the incommensurate modulation and the va riation of its period were also found in the bulk of the films, as wel l as misfit dislocations near the Bi2Sr2CaCu2O8+delta/SrTiO3 interface .