MgB2 superconducting thin films on Si and Al2O3 substrates

Thin films of the superconductor MgB2 were prepared by three different proc edures on sapphire and silicon substrates. Boron thin films, ex situ anneal ed in magnesium vapour, resulted in textured polycrystalline films with cry stal dimensions below about 1 mum, onset critical temperature T-con near 39 K and width of phase transition DeltaT less than or equal to 1 K. Both, ex situ and in situ annealed co-deposited boron and magnesium thin films on s apphire and silicon substrates give smooth nanocrystalline films. DC proper ties of nanocrystalline MgB2 films co-deposited on silicon substrate reache d T-con = 33 K and zero resistance T-c0 = 27 K, the highest values received until now on Si substrates. In addition, microwave analyses prove the exis tence of unconnected superconducting parts of the film below 39 K. This res ult confirms the possibility to synthesize nanocrystalline superconducting MgB2 thin films on silicon substrate with critical temperature near 39 K, p repared by vacuum co-deposition of boron and magnesium films. (C) 2001 Else vier Science B.V. All rights reserved.