Electronic transport in ultrathin epitaxial Pb films on Si 111/ surfaces

Epitaxial metallic films are candidates for two-dimensional 2D.electronic systems. In that respect, the DC conductivity is a good tool to check the electronic structure for quantum phenomena. The annealed Pb films on the Si 111.7=7 and on the Si 111.ʹ3 =ʹ3 Pb surfaces show a very contrary behavior to that of classical metals. Whereas at 8 K and a coverage above 6 monolayers ML.the conductivity is well described by the classical Drude model with the mean free path in the order of the film thickness, at low coverages, a metal–insulator transition MIT.is observed. The conductivity shows different regimes pointing to strong localization, weak localization or classical behavior depending on film thickness, annealing and measuring temperature. Structural changes modify directly the conductivity. Superconductivity with the critical temperature close to the bulk value is observed in annealed films with a thicknesses down to 4 ML. Resistivity oscillations during the growth of the film on Si 111.-ʹ3 =ʹ3 Pb with 1 ML and 2 ML period are reported. q2000 Elsevier Science B.V. All rights reserved