Properties of sputtered superconducting films of Bi2Sr2CaCu2Ox made by low-temperature in situ growth

Superconducting films of Bi2Sr2CaCu2Ox have been fabricated on single-crystal MgO substrates by a low-temperature in situ process. Using a substrate temperature Ts∼645 degree C, metallic films with a superconducting onset of 90--100 K and an extrapolated Tc0=56 K have been obtained. X-ray diffraction shows the films to be c-axis oriented. Electron microscopy reveals that the films are not significantly smoother than films which were post-annealed at 865 degree C, and that some segregation into nonsuperconducting phases had occurred. The exact mechanism by which crystallization and superconductivity occurs at such low temperatures is not yet known, but it can be speculated that the surface atoms are less constrained and thus have a smaller energy barrier to overcome in forming a crystal structure