The observation of tin islands in Nb3Sn thin films deposited by magnetron sputtering

Superconducting Nb3Sn thin films have been produced on copper substrate by dc magnetron co-sputtering technique successfully. XRD and magnetic moment measurement demonstrate the exist of Nb3Sn crystal. By changing the ratio between niobium target sputtering current to tin target, the tin concentration in different films is varied. However, the experiment results indicate critical temperature T-C of different Nb3Sn thin film are nearly invariable while the composition of Nb-Sn of those are changed. Highest T-C of those films annealing at 650 degrees C are around 12K, while 750 degrees C annealing increase it to 15K. The SEM and element analysis results manifest inhomogenous distribution of tin atoms, where some tin islands appear over the film. The exist of tin-rich areas like tin islands is responsible for such particular performance of Nb3Sn films.