Microwave surface resistance of reactively sputtered NbN thin films

The surface resistance of niobium nitride (NbN) thin films has been measured at 7.78 and 10.14 GHz in the temperature range of 1.5 to 4.2 K. The films were reactively sputtered on sapphire substrates to a thickness of approximately one micron. The surface resistance was determined by measuring the quality factor (Q) of the TEO11 mode of a lead-plated copper cavity where the NbN served as one end-cap of the cavity.