PREPARATION OF ULTRATHIN BI-SR-CA-CU-O SUPERCONDUCTING FILMS BY METALORGANIC CHEMICAL VAPOR-DEPOSITION

Ultrathin Bi-Sr-Ca-Cu-O films close to a single unit cell [c = 3.1 nm for Bi2Sr2CaCu2Ox (2212) phase] were grown on a (100) MgO substrate by metalorganic chemical vapor deposition. The ultrathin film, having an average thickness of 3.5 nm, exhibited a zero-resistance superconducting transition, T(c,0) = 64 K, comparable with the T(c,0) of much thicker films, whereas the superconducting property of thinner films than 3.5 nm was drastically deteriorated. The x-ray diffraction (XRD) measurement of the ultrathin films showed that the reflection peaks from 00l contributed to a 2212 phase were observed even in the 2.2-nm-thick film, and that its c-axis lattice constant was consistent with that of a bulk 2212 phase. On the other hand, the thicker films than 5.5 nm mainly consisted of the Bi2Sr2Ca2Cu3Ox (2223) phase with a trace amount of the 2212 phase from the XRD patterns.