Effects of oxygen addition on superconductivity of sn cluster-assembled films

Sn cluster-assembled films have been produced using a plasma-gas-condensation cluster deposition apparatus with and without 02 gas addition in a sputtering chamber. The Sn clusters prepared without 02 gas addition agglomerated On the substrate and formed larger islands. They exhibited a broad superconducting transition below 3.7K, suggesting that their transition temperature T-c depends on their cluster size. When 02 gas was added to the cluster source, cluster size decreased and the agglomeration was prevented. The Sn cluster-assembled film prepared at an O-2 gas flow rate R-O2 = 0.05 sccm showed a sharp superconducting transition at T-c = 4.0K, which was higher than the T-c of bulk beta-Sn (T-c(b) = 3.7 K). Magnetization measurements indicated that the Sn cluster-assembled films prepared at R-O2 <= 0.1 sccm were type II superconductors.