Superconductivity in Superstructure of Bi-based Oxide Thin Films

Bi2Sr2Can−1CunO4+2n superstructure films have been synthesized by three target RF magnetron sputtering by the alternate deposition of BiO, SrCu0.5O1.5 and CaCuO2 layers. Layered structure of the completely c-textured films formed on the MgO substrate are characterized quantitatively by x-ray techniques. By x-ray specular reflection and the Laue’s oscillatory pattern in x-ray diffraction, the number of units in the films can be analyzed. The ratio of the intergrowth mixture of succeeding phases is evaluated by applying the concept of superlattice to the analysis of x-ray diffraction pattern. The feed back can be applied to the growth condition (deposition time for each layer) using these results in combination with the Rutherford backscattering composition analysis. A control of the film thickness within a scale of monolayer and a control of phase purity as high as 99% can be achieved by these methods. It is shown that the T c of the artificial films can be understood by the hole concentration in the CuO2 layers in each structure which decreases with the increase of the number of CuO2 layers in a unit. It is suggested that the T c of intergrowth and superstructure films can be explained by the charge transfer which results in the change in the hole concentration in the Cu layers.