STM OBSERVATION OF DISLOCATION CHAINS SUITABLE FOR FLUX-PINNING IN YBA2CU3O7-X FILMS

Systematic variations of the film-growth conditions during pulsed-lase r deposition (PLD) with regard to substrate temperature, oxygen partia l pressure and substrate quality, allow us to establish correlations b etween the as-grown defect structure and the current transport propert ies of c-axis oriented YBa2Cu3O7-x films. By investigating the film su rface with scanning electron microscopy (SEM) and scanning tunneling m icroscopy (STM) the nature and the density of various defects as well as the general film-growth mode were determined. SEM pictures show the overall surface roughness and the presence of other phases (outgrowth s), while higher-resolution STM pictures reveal small-scale defects do wn to the nm range. Transport current measurements on patterned parts of the same films show differences in the magnitude of J(c) as well as in its field and angle dependence. Influences of the defect structure on intrinsic pinning, weak-link properties and special features in th e angular dependence of J(c) are discussed. Dislocation chains extendi ng over several layers along the c-axis within the terraces of growth spirals are of special interest with regard to flux pinning. The exist ence of these dislocation chains can be directly implied from the pres ent data. A higher substrate roughness and a faster growth speed of th e terraces along the ab plane seem to favor the appearance of the disl ocation chains.