Observation of the insulator-superconductor transition on solid inert gas and other substrates

Observations of the insulator-superconductor transition in amorphous ultrathin films of Bi deposited on solid xenon are presented. The resistance separatrix is found to be close to h/4e² and the crossover thickness close to 25 angstrom for all substrates. I-V studies and Aslamazov-Larkin analyses indicate that the superconductivity is inhomogeneous. Screening effects are observed, with the transition temperature increasing as the relative permeability of the substrate is increased, when studying films on quartz and Ge. The resistance separatrix that defines the transition remains unaffected. These results may be qualitatively understood in terms of a percolation-type model.