The Proximity Effect in Systems of Ultrasmall Superconducting Grains

We compare transport and proximity effect measurements on granular systems in which the grains are about 40-80 A in diameter to those of systems reported in the past where the films were either uniform or granular with grain diameters on the order of 200 A. These systems show unique characteristics which lead to the speculation that their properties are determined by the fact that many of the grains are too small to sustain bulk superconductivity.