Superconducting MgB2 thin films were prepared on Al2O3(00▪1) substrates using the 2-step method. B thin films were deposited by electron-beam evaporation followed by ex situ annealing in a Mg vapour environment. With proper annealing conditions, the TC of MgB2 thin films was about 39K and their JC values were above 107A/cm2 at 15K. Furthermore, JC was increased on reducing the thickness of as-grown MgB2 film by the Ar ion milling below a certain temperature although TC and its transition width were slightly degraded. Through detailed study of the microstructural evolution of the MgB2 layer during the ex situ annealing with scanning electron microscopy and transmission electron microscopy, MgB2 was found to nucleate at the amorphous B layer and then grow into and out of the a-B film simultaneously, resulting in 2 different MgB2 layers with different grain morphologies.

Superconducting Properties and Microstructures of MgB2 Thin Films Prepared by the ex situ Annealing Process. S.H.Moon, H.M.Kim, S.S.Yim, K.B.Kim, Y.W.Kim, S.I.Yoo, H.N.Lee: Superconductor Science and Technology, 2004, 17, S15-9