Pits on the surfaces of epitaxial c-axis YBa2Cu3O7-delta thin films grown on vicinal SrTiO3 substrates

The reoccurrence of pits has been found on the surfaces of c-axis YBa2 Cu-3 O7-delta (YBCO) films grown epitaxially on 10 degrees vicinal SrTiO3 subst rates by pulsed laser deposition. They are always associated with films wit h a step-terrace structure, while polycrystalline films have no pits. Pit f ormation is attributed to the large interfacial stress induced by vicinal s ubstrate and oxygen deficiency of the YBCO film during the tetragonal-to-or thorhombic (TO) phase transition, which cannot be released by forming twins , and leads to rupturing of the film surface. By reducing the oxidation par tial pressure for the T-O phase transition to 80 Pa, no pits were formed, a nd the YBCO film is superconducting at 60 K.