As-grown MgB2 thin films deposited on Al2O3 substrates with different crystal planes

Abstract

We present the results of an investigation of the crystal structures and superconducting properties of as-grown MgB2 superconducting thin films deposited on Al2O3 substrates having different crystal planes (C- and R-planes). The MgB2 thin films were prepared by a multiple-target sputtering method without performing a post-annealing process. The MgB2 films deposited on the C-plane Al2O3 substrates were found to have a c-axis orientation, from the results of 2θ/θ x-ray diffraction (XRD) measurements. However, there were no MgB2 peaks for the films grown on the R-plane Al2O3 substrates. Even though the maximum Tc values of both films deposited on the C- and R-plane Al2O3 substrates were nearly the same, Tc,onset ∼ 28 K and residual resistivity ratio ∼ 1.2, it is very interesting to note that the resistivity of the films on the C-plane Al2O3, ρ ∼ 70 μΩ cm at 40 K, was lower than that on the R-plane Al2O3, ρ ∼ 300 μΩ cm at 40 K. These results indicate that the grain size of MgB2 in the films deposited on the C-plane Al2O3 substrates was larger than that on the R-plane Al2O3, indicating a good agreement with the XRD measurements. The surface morphology of the as-grown MgB2 thin films was investigated using scanning electron microscopy. The surfaces of the films on the C- and R-plane Al2O3 substrates were found to be very flat and smooth. This result indicates the high potential for fabricating Josephson tunnel junctions using as-grown MgB2 thin films.Presented at the IUMRS-ICEM conference, Xi'an, China, 10–14 June 2002.