MgB2 superconducting thin films on Si and Al2O3 substrates

Thin films of the superconductor MgB2 were prepared by three different procedures on sapphire and silicon substrates. Boron thin films, ex situ annealed in magnesium vapour, resulted in textured polycrystalline films with crystal 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 sapphire and silicon substrates give smooth nanocrystalline films. DC properties of nanocrystalline MgB2 films co-deposited on silicon substrate reached 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 existence of unconnected superconducting parts of the film below 39 K. This result confirms the possibility to synthesize nanocrystalline superconducting MgB2 thin films on silicon substrate with critical temperature near 39 K, prepared by vacuum co-deposition of boron and magnesium films. (C) 2001 Elsevier Science B.V. All rights reserved.