STM observation of dislocation chains suitable for flux pinning in YBa 2Cu 3O 7− x films

Abstract

Systematic variations of the film-growth conditions during pulsed-laser deposition (PLD) with regard to substrate temperature, oxygen partial pressure and substrate quality, allow us to establish correlations between the as-grown defect structure and the current transport properties of c-axis oriented YBa 2Cu 3O 7− x films. By investigating the film surface with scanning electron microscopy (SEM) and scanning tunneling microscopy (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 (outgrowths), while higher-resolution STM pictures reveal small-scale defects down 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 the angular dependence of J c are discussed. Dislocation chains extending over several layers along the c-axis within the terraces of growth spirals are of special interest with regard to flux pinning. The existence of these dislocation chains can be directly implied from the present data. A higher substrate roughness and a faster growth speed of the terraces along the ab plane seem to favor the appearance of the dislocation chains.