Properties of Very Thin Aluminum Films

Thin films of aluminum have been produced in the thickness range of 1000–30 Å in small area samples with photoetched edges. The superconducting transition temperature Tc, the critical magnetic field Hc, and the room-temperature conductivity have been measured as a function of thickness d. The results indicate that films as thin as 30 Å act essentially as uniform layers in which the crystal size is approximately equal to the film thickness. The transition temperature was found to vary linearly with d−1. Hc (T) was measured from Tc to 0.4°K. For thickness from 1000 to 200 Å, Hc∼d−3/2, as expected from the Ginzburg-Landau theory. For d 200 Å, Hc is paramagnetically limited to about 49 kOe = 19.6Tc, slightly above the Clogston limit.