Effect of the nitrogen-argon gas mixtures on the superconductivity properties of reactively sputtered molybdenum nitride thin films

We report on the superconducting properties of nanocrystalline molybdenum nitride thin films grown by reactive DC sputtering at room temperature with a N2:Ar mixture. Thin films grown using 5% N2 concentration display Tc = 8 K, which is gradually reduced to 5.8 K for 30% N2 concentration, producing changes in nitrogen stoichiometry of the samples from Mo2N to Mo2N1+x (0 ≤ x < 0.4). The Tc is abruptly reduced and disappears for N2 concentration between 30% and 40%, which can be attributed to an increment in the disorder due to phase coexistence between cubic γ-Mo2N and non-superconducting amorphous MoN (dominant for N2 concentration >40%).