In-situ formation of BSCCO thin films by plasma assisted thermal evaporation

Thin films of the superconductor Bi-Sr-Ca-Cu-O (BSCCO) have been prepared by thermal evaporation in an evaporator featuring an RF-excited oxygen plasma generator. Formation of the 2212 phase is obtained in situ, as confirmed by X-ray analysis. The films require postannealing, however, in order to exhibit a superconducting transition. Specifically, postanneals are required to obtain critical temperatures of up to 75 K; 1330 Pa is the minimum annealing pressure. The authors report the study of the superconducting properties as a function of oxygen annealing pressure as well as a characterization of the oxygen plasma. An investigation of the surface morphology was performed using a force microscopy (AFM) and a tunneling microscopy (STM). The latter clearly shows terraces and steps with a height of 1.5 nm, or multiples thereof, corresponding to one-half of the c-axis lattice constant of the 2212 compound. The AFM, on the other hand, shows a drastic difference between as-grown and annealed films, even when the former are sometimes insulating.