Reactively sputtered superconducting niobium nitride surfaces

Recently niobium nitride has been attracting attention for stabilizing Nb surface. While it is a thin protective layer, the NbN itself is an interesting superconductor. RF characteristics of the NbN films are not clear yet, however. The reactive DC sputtering deposition of NbN on cavity surface has been studied experimentally. In this method, glow discharge is built up in nitrogen atmosphere between a Nb cathode and a Cu (or Ta) anode. Niobium is sputtered from the cathode, and reacts with N2 on a substrate surface. Nb is a very good material for substrate, and anodized aluminum layer can be used as a substitute. The film deposition on plane and cylindrical substrates was tested. Promising results were obtained especially as to the method to prepare the good, uniform NbN films. (Mori, K.)