Superconducting YBa₂Cu₃O₇ films grown on TiO₂ buffer layers derived from various processes

YBa₂Cu₃O₇ (YBCO)/TiN and YBCO/TiO₂ bilayer structures have been prepared on SrTiO₃ (STO)(100) substrates by in situ pulsed laser deposition (PLD). The TiN films were originally intended to serve as the lower contact electrode for studying the c-axis transport properties of YBCO thin films. It was found that, under the optimum conditions of depositing YBCO thin films, the TiN(100) layer was oxidized and transformed into rutile TiO₂(110) film. On the other hand, pure anatase TiO₂(001) films were prepared by PLD using a rutile TiO₂(110) substrate as the target. YBCO films grown on both phases of TiO₂ films show virtually the same transport properties of typical good quality single-layer YBCO films. Comparative studies of depositing YBCO films directly onto a dc-sputtered TiO₂ template commonly used in the selective epitaxial growth process have, however, resulted in formation of a nonsuperconducting YBCO top layer. Experiments including interfacial X-ray absorption spectroscopy for determining the possible interactions occurring at the YBCO and TiO₂ interface are reported.