SURFACE-RESISTANCE AND MORPHOLOGY OF YBCO FILMS AS A FUNCTION OF THICKNESS

We have examined the thickness dependence of the growth morphology and surface resistance R-s of laser ablated YBa2Cu3O7-x films with transi tion temperatures over 89 K and critical current densities greater tha n 10(6) A/cm(2) at 76 K. The thickness was varied from 50 to 1600 nm w hile all other deposition conditions were maintained constant. The mic rostructure has been characterized by scanning electron microscopy and scanning tunneling microscopy (STM). The films exhibit two-dimensiona l island growth at all thicknesses and the island density continuously decreased with film thickness as a power law with an exponent of -0.5 . The surface resistance was measured at 76 K with a dielectric rod re sonator. for films less than 300 nm thick, the fields penetrated the s uperconducting films, causing a rapid increase in the apparent R-s wit h decreasing film thickness. Films thicker than 800 nm showed microcra cks and the R-s increased sharply, and no resonance was observed above 1000 nm.