METALLIC AND NONMETALLIC CONDUCTIVITY OF THIN EPITAXIAL SILVER FILMS

The conductivity of thin epitaxial Ag films on Si(111) surfaces is studied as a function of film thickness [0-125 monolayers (ML)] and temperature (20-300 K) under ultrahigh vacuum conditions. Different regimes of conductance can be distinguished. Films thicker than 2 ML behave metallically with small corrections due to weak localization effects. The thickness dependence of the elastic mean free path is given by electron scattering at the surfaces and at bulk defects. The electron states in films thinner than 2 ML are obviously localized. The conductance measured during the deposition of Ag on Si(111) at 50 K may be described in terms of a two-dimensional percolation problem.