Influence of the nature of the substrate on the growth of superconducting niobium films

The superconducting properties of niobium films sputtered onto the inner walls of radiofrequency cavities, including their surface resistance to 1.5 GHz microwaves, have been studied as a function of the nature of the substrate. Films grown on oxide-free copper or niobium behave differently from films grown on other substrates. The results are analysed in terms of the film texture and internal stresses.