SURFACE MICROSTRUCTURES AND PROPERTIES OF YBA2CU3O7-X FILMS BY BIAS-MASKED ON-AXIS RF-SPUTTERING

YBa2Cu3O7-x films were deposited on LaAlO3 (001) substrates by masked on-axis sputtering with growth rates as high as 210 nm/h. Superconduct ing properties and surface morphologies of these films can be optimize d by applying an appropriate positive substrate bias. Scanning tunneli ng microscopy and atomic force microscopy (AFM) analyses of these film s reveal all the films described have a screw dislocation growth mecha nism. High screw dislocation densities (almost-equal-to 2 x 10(9) disl ocations/cm2) are observed on films grown with +27 and +30 V substrate biases respectively. In addition, AFM observations also reveal insula ting 10 nm size nanoparticles on films growth with a +27 V bias. Such +27 V biased films display high normal state resistivities around 280 muOMEGA cm at 300 K and high critical currents of about 3 x 10(6) A/cm 2 at 77 K and zero applied field. Finally, we have observed the growth of double screw dislocation pairs which may be associated with line d efects on the substrate. As far as we know this is the first direct ob servation of such clockwise and anticlockwise pairs of screw dislocati ons.