Influence of the SiO underlayer on the superconductor-insulator transition in amorphous Bi films

We have measured the temperature (T) dependence of the resistance per square R for a series of ultrathin Bi films quench-condensed onto different SiO underlayers ranging in thickness from zero to approx. 2 angstrom. The R-T characteristics of Bi films on a 4.3 angstrom-thick layer of SiO are different from those on the layers thicker than 10 angstrom, possibly because of the inhomogeneity in Bi films. The results suggest that insufficient thickness of an underlayer causes a larger value of the critical resistance for the superconductor-insulator transition in quench-condensed Bi films.