Effects of nitrogen gas addition on superconductivity of tin cluster-assembled films

Abstract Sn cluster-assembled films have been produced by a plasma-gas-condensation (PGC) cluster deposition apparatus with and without N2 gas addition in the cluster source. The Sn clusters prepared without N2 gas agglomerated on a substrate and formed larger islands. They exhibited a broad superconducting transition below 3.7 K, suggesting that Tc depended on the cluster size. When N2 gas was introduced in the cluster source, the cluster size became smaller and the agglomeration was prevented. The Sn cluster-assembled film prepared with the N2 gas flow rate, R N 2 = 0.20 sccm , showed a sharp superconducting transition at Tc=3.8 K. The sample prepared with R N 2 = 0.40 sccm had no superconducting transition down to 1.8 K. The magnetization measurements indicated that these films prepared with R N 2 ⩽ 0.3 sccm were type II superconductors.