Tcsuppression and critical fields in thin superconducting Nb films

Thin Nb films from 30 to 150 Å thick have been electron-beam evaporated onto sapphire substrates with aluminum overlayers, then deposited to protect the surface. $T_c\text{'}\mathrm{s}$ and magnetoresistance were found to be consistent with localization models, and measured parallel critical fields fit a generalized Ginzburg-Landau theory. Perpendicular critical fields, however, were found to have an anomalous curvature near $T_c$. These results, we believe, are due to the disorder of the film and have also been seen in other systems.