Tunneling, resistive and structural study of NbN and other superconducting nitrides

A straightforward method for producing metal nitrides, which we call Thin Film Diffusion (TFD), has been developed. With this technique we produced films of cubic nitrides (NbN, ZrN, VN, TiN) with superconducting transition temperatures up to 17.25K in NbN (equal to the highest known in this material), and up to 9.4K in VN (0.6K higher than the highest previously reported value). Resistive transitions are less than 0.1K in width, indicating, together with x-rays, that the samples are homogeneous and essentially single BI phase. In NbN the relatively low resistivity ρ(20K) = 65 μΩcm and metallic resistance ratio ρ(300K)/ρ(20K) - 1.2 were found. TFD films open up new possibilities in tunneling and other experiments on cubic nitrides. Our present results include determination of the strong coupling parameter 2Δ(0)kTc= 4.31 and of the electron-phonon coupling function in NbN. is found to have a peak at ∼13 meV, which explains the strong-coupling nature of NbN. In resistive studies we found an interesting similarity between the low temperature resistivity behavior of cubic nitrides and A-15 superconductors.