Superconducting Properties and Structure of Reactively Sputtered Niobium Carbide Thin Films

Abstract

Niobium carbide thin films have been sputter deposited in a reactive argon and methane plasma at substrate temperatures of 700 °C. The background pressure prior to sputtering was typically in the low 10−7-Torr range, the total sputtering pressure was maintained at 2×10−3 Torr and the partial pressure ratios of argon and nitrogen were monitored and controlled with a residual gas analyser. Jc–H characteristics were measured by applying a pulsed field and pulsed current method and transition temperatures were determined by recording resistivity versus sample temperature. The structure was studied by x-ray diffraction. Hc2 is about 40 kOe and the highest Tc is 9.6 K. Several carbide phases and their mixtures were observed and have been correlated to the partial pressure ratios of the plasma.