In-situ annealing effects on MgB/sub 2/ thin films fabricated by electron beam deposition

Although the as-grown method is becoming the main current for fabrication of MgB/sub 2/ thin films, the in-situ annealing method is still indispensable and effective for obtaining thin films with a high zero resistivity temperature and current density. We have investigated the effects of in-situ annealing on the superconducting properties of MgB/sub 2/ thin films. MgB/sub 2/ thin films were fabricated by electron beam epitaxy on C-plane sapphire (Al/sub 2/O/sub 3/) substrate. Thin films were produced by simultaneously evaporating B and Mg metal in a high vacuum of 3/spl times/10/sup -7/ Pa. Substrate temperature was 265/spl deg/C. The zero resistivity temperature of the as-grown thin films was 31 K. Electron beam deposition was followed by in-situ annealing in a high vacuum. In the optimal annealing process (a thin film is heated at 600/spl deg/C for one hour) we have consistently obtained thin films with a zero resistivity temperature of 35 K. In contrast, the critical current density of MgB/sub 2/ thin films was decreased by annealing. This suggests that the crystal grain boundaries in the MgB/sub 2/ thin films are working as a flux pinning site, and crystal growth from annealing brought about the reduction of current density.