Critical Temperatures of Thin Aluminum and Lead Superconducting Films.

The critical temperatures (T sub c) were measured resistively. The Al films were evaporated from Al2O3 boats onto cold substrates (approximately 4.5 K) of z-cut crystalline quartz and poly(n-vinylcarbazole) (PVK). The maximum T sub c for Al films on quartz was 5.3 K. Al films on PVK show less enhancement of T sub c than the films on quartz. The Pb films were evaporated onto cold substrates (4.5 K and 77 K) of z-cut crystalline quartz, epitaxially grown PbTe and amorphous PbTe. Films were also formed by co-evaporation of Pb and PbTe. Depressed T sub c's were observed for very thin Pb films in close contact with PbTe. No evidence of a superconducting state in pure PbTe was observed. The results may be understood within the frame- work of existing phonon-induced superconductivity theories and are in general agreement with trends observed by other investigators.