Properties of superconducting vanadium nitride sputtered films

Abstract

High-quality films of VN were prepared by reactive dc sputtering with the use of a triode source. The films were characterized by x-ray diffraction, temperature-dependent electrical resistivity, and superconducting ${T}_{c}$. Deposition onto single-crystal sapphire substrates heated to 600 \ifmmode^\circ\else\textdegree\fi{}C resulted in uniaxial growth of grains along the [111] direction. Residual resistance ratios as high as 5 were obtained and ${T}_{c}$ up to 8.9 K. The dependence of ${T}_{c}$ on a lattice parameter differs considerably from previous reports in the literature. The temperature-dependent resistivity was found to be consistent with the parallel-resistor model. Tunnel junctions were fabricated by direct plasma oxidation of the film surface and preliminary quasiparticle results confirm that VN exhibits strong electron-phonon coupling. Josephson junctions utilizing an artificial CdS barrier display diffraction characteristics leading to an upper-bound estimate of the penetration depth of \ensuremath{\lambda}\ensuremath{\sim}1300 A\r{}. .AE