I n s i t u epitaxial growth of Bi2(Sr,Ca)3Cu2Ox films by ion beam sputtering with an atomic oxygen source

I n situ epitaxial growth of Bi2(Sr,Ca)3Cu2Ox films was performed by ion beam sputtering in atomic oxygen ambience at the substrate temperature of 640 °C. The films showed an epitaxial growth in which the a and b axes were parallel to 〈100〉 MgO, and the superstructure according to the incommensurate modulation along the b axis was also observed. The superconducting properties of the as-grown films seemed to sensitively depend on the oxidation treatment during the cooling down process. The zero resistivity temperature Tc(R=0) of a 600-Å-thick film cooled down in the same atomic oxygen density as the film growth ambience was 60 K, but it increased up to 80 K after a post-deposition annealing at 500 °C for 1 h in air. In contrast, as-grown films cooled down in insufficient oxidation ambience showed the Tc(R=0) of 76 K without post-deposition annealing. The control of the oxygen concentration is critical for the superconductivity of as-grown films.