NONMETALLIC CONDUCTIVITY OF EPITAXIAL MONOLAYERS OF AG AT LOW-TEMPERATURES

Epitaxial metallic monolayers are models for two-dimensional conductio n. They provide well-ordered monatomic films with an atom distance as in the bulk. Measurements of the de conductivity of epitaxial Ag films on a clean Si(111) 7 x 7 substrate at about 100 K reveal that the con ductance for a thickness down to nearly a monolayer is well described by a simple Drude model with a mean free path given by the film thickn ess. For lower temperatures (down to nearly 4 K) the conductance of ve ry thin films is reversibly decreased by orders of magnitude. Whereas annealing increases the mean free path for thick films up to twice the thickness, the films with a thickness of less than 2 monolayers show no annealing effect. The results may be discussed with models of amorp hous or granular films. The lack of agreement with theoretically predi cted temperature dependences may be due to the special structure of ep itaxial films. [SO163-1829(98)01639-7].