Superconductor-insulator transitions in quench-condensed Bi films on different underlayers

We report on thickness-tuned superconductor-insulator transitions in amorphous Bi films quench-condensed onto underlayers of Ge, Sb, and SiO. Bi films on Ge and SiO have almost the same values, similar to 5.2 k Omega of the critical resistance per square at temperatures down to 0.9K, whereas those on Sb have a larger value of 7.5 k Omega. On the insulating side, the conductance of Bi films on Sb depends logarithmically on temperature in contrast to the thermally activated form of those on SiO and Ge. The results suggest that the peculiar temperature dependence of the resistance per square of Bi films on Sb is the behavior characteristic of an Sb underlayer which becomes insulating from semimetal by quench-condensation. (C) 2007 Elsevier B.V. All rights reserved.