MOLECULAR-BEAM EPITAXY DEPOSITED THIN-FILMS OF BISMUTH COMPOUND SUPERCONDUCTORS

Thin films of superconducting BiCaSrCuO have been grown by molecular beam epitaxy depositions of Bi, Cu, and CaF2/SrF2 on MgO and SrTiO3 followed by a high-temperature oxygen anneal. The films showed a fairly wide transition of 20 K at a Tc of 80 K. Residual amounts of fluorine, detected with secondary-ion mass spectrometry, are believed to cause the broad superconducting transition. X-ray diffraction analysis of the superconducting films revealed strongly c-axis oriented films consisting of Bi2CaSr2Cu2O8 and Bi 2Sr2Cu1O6 phase. Surface structure studies, with scanning electron microscopy and scanning tunneling microscopy, show oriented 1 μm sized very smooth flat grains of superconducting phase in the plane of the film with islands of CuOx scattered on top of these.