THICKNESS DEPENDENCE ON THE SUPERCONDUCTING PROPERTIES OF THIN NB FILMS

The thickness dependence of the superconducting properties of Nb films has been studied by resistance and ac magnetic susceptibility measure ments. The film thickness was varied from 825 to 200 angstrom by anodi zing a single dc sputtered film in order to minimize any sample-to-sam ple preparation variations. For films 400 angstrom thick and greater, the normal-state resistivity at 10 K is constant and the suppression o f the superconducting transition temperature T(c) with decreasing thic kness is explained in terms of both the proximity effect and weak loca lization. The magnetic susceptibility results show that the diamagneti c transition broadens with decreasing thickness and increasing ac fiel ds as a result of the effective fields becoming greater than the criti cal field H(c1) of Nb.