Enhanced Suppression of Superconductivity in Amorphous Films with Nanoscale Patterning

We have measured the thickness dependence of the superconducting critical temperature, $T_c(d_{\rm Bi})$, in amorphous Bi/Sb films patterned with a regular array of holes as well as nanoscale thickness variations. We find that the mean field $T_c$ is suppressed relative to simultaneously produced unstructured films of the same thickness. Surprisingly, however, the functional form for $T_c(d_{\rm Bi})$, remains unaffected. The role of the thickness variations in suppressing $T_c$ is compared to the role of the holes, through parameterization of the surface, as measured through AFM/SEM and a proximity effect calculation. These results suggest that these two nanoscale modifications suppress $T_c$ about equally and are consistent with $T_c$ being determined on a microscopic length scale.