Pits on the Surfaces of Epitaxial c-Axis YBa₂Cu₃O_7-δ Thin Films Grown on Vicinal SrTiO₃ Substrates

The reoccurrence of pits has been found on the surfaces of c-axis YBa₂Cu₃O_7-δ (YBCO) films grown epitaxially on 10°vicinal SrTiO₃ substrates by pulsed laser deposition. They are always associated with films with a step-terrace structure, while polycrystalline films have no pits. Pit formation is attributed to the large interfacial stress induced by vicinal substrate and oxygen deficiency of the YBCO film during the tetragonal-to-orthorhombic (T-O) phase transition, which cannot be released by forming twins, and leads to rupturing of the film surface. By reducing the oxidation partial pressure for the T-O phase transition to 80Pa, no pits were formed, and the YBCO film is superconducting at 60K.