In Situ Oxidation of Superconducting YBCO Films by a Supersonic ${\rm O}_{2}$ Beam

We report on the successful implementation of a supersonic molecular oxygen (O₂) beam for the in situ oxidation of superconducting YBCO films. The beam is produced by a specially designed array of conical nozzles that were laser machined in a platinum foil. The array was mounted in proximity of the deposition area of a thermal co-evaporation system for YBCO film deposition. After a brief description of the basic concepts underlying the physics of supersonic beams, we describe the design of the nozzle implemented in our system. Then, we illustrate and discuss the preliminary results obtained by varying a number of key parameters of the supersonic beam. Most important parameters turn out to be the input O₂ pressure and the nozzle-film distance. We show that excellent electrical properties with zero-resistance superconducting critical temperatures, T_c, in excess of 90 K are reproducibly obtained over the entire 20 cm X 20 cm deposition area. These results were obtained using various types of substrates relevant to coated conductor fabrication, including Zr-doped CeO₂ buffered cube-textured Ni-W and MgO buffered hastelloy substrates.