Pulsed laser deposition and nanometer scale characterization of YBa2Cu3O7−δ thin films by scanning probe methods

Scanning probe methods (SPM) are applied to study YBa2Cu3O7−δ (YBCO) thin films grown on SrTiO3(100) substrates by pulsed laser deposition (PLD). Prior to deposition the surface of the SrTiO3 substrates is investigated by scanning force microscopy (SFM). The misorientation of the substrates as determined from SFM images is less than 0.2° off the (100) plane. Since the misorientation of the substrates varies from wafer to wafer a special half-shadow technique is applied yielding YBCO thin films with a gradient in thickness in order to study the growth morphology as a function of film thickness by scanning tunneling microscopy (STM). At a coverage of less than one YBCO monolayer we observe by STM the nucleation of YBCO islands at SrTiO3 steps. Up to a film thickness of about 40 nm two-dimensional islands are spreading whereas at larger film thickness growth hills are observed.