Scanning tunneling microscopy of the surface morphology of YBa2Cu3O<i>x</i> thin films between 300 and 76 K

Abstract

Scanning tunneling microscopy (STM) images of YBa2Cu3Ox (YBCO) thin films show different growth mechanisms depending on the deposition method and substrate material. We present images of YBCO films sputter deposited onto MgO and SrTiO3, and laser ablated onto LaAlO3 showing screw dislocation and ledge growth mechanisms. At room temperature we observed an anomalous tunneling conductance near the edge of growth steps which causes a large apparent step-edge height in the STM image. This effect decreases with decreasing temperature, so that the step height approaches the expected value for one unit cell of 1.2 nm at 76 K. This phenomenon reflects changes in either the surface tunneling barrier or tunneling density of states upon cooling.