Improvements of performance on sputter-coated niobium films for superconducting cavities by adding a NbN interlayer

A new type of superconducting film is studied at Peking University in order to improve the properties of sputter-coated films for superconducting cavities. NbN film and NbN–Nb film have been prepared by DC diode sputtering technology at certain nitrogen content and temperature. NbN film is prepared between copper and Nb film as a barrier against copper diffusion into Nb. Micro-structure analyses show that the NbN–Nb films grow well on the copper substrate. The Tc of the Cu–NbN–Nb increases to 9.5 K compared to the 9.2 K transition temperature of bulk Nb.