Microstructure of Interfaces in YBa2Cu3O7-x Thin Films

Highly oriented, high-quality thin films of the high-temperature superconductor, YBa2Cu3O7-x (henceforth referred to as 123 or YBCO), are now successfully and routinely produced by a variety of in situ deposition techniques [1–12]. In particular, the techniques of laser ablation [1, 2] and off-axis sputter deposition [4, 6], both using a single, composite target, have emerged as the most reliable in situ physical processes producing uniform, high-quality films over relatively large substrate areas. The best films are c-axis oriented and have T c ’s as high as 90 K with transition widths of less than 1 K and J c (77 K) > 106 A/cm2. Organometallic chemical vapor deposition has also produced large area films with comparable properties [11, 12]. These thin films, although highly oriented and exhibiting superior superconducting properties, are not single crystals. Rather they exhibit a rich microstructure of grain boundaries, stacking faults, second phases, dislocations, and other crystallographic defects and interfaces, the characteristics of which depend on the orientation and composition of the films, as well as on the processing parameters. Thin-film processes offer the capability of controlling microstructures on a fine scale by varying these synthesis conditions; because of the two-dimensional nature of film growth these processes also allow for synthesis of artificially layered structures. We therefore have the opportunity to design thin films with specific, controlled sets of interfaces.