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 measurements. The film thickness was varied from 825 to 200 angstrom by anodizing a single dc sputtered film in order to minimize any sample-to-sample preparation variations. For films 400 angstrom thick and greater, the normal-state resistivity at 10 K is constant and the suppression of the superconducting transition temperature T(c) with decreasing thickness is explained in terms of both the proximity effect and weak localization. The magnetic susceptibility results show that the diamagnetic transition broadens with decreasing thickness and increasing ac fields as a result of the effective fields becoming greater than the critical field H(c1) of Nb.