Electronic transport in ultrathin gold films on Si(111)

The morphology and electronic transport of ultrathin Au films with thicknesses d = 1 − 5 monolayers (ML) deposited on Si(111)7 × 7 surfaces is investigated by in situ scanning tunneling microscopy and electrical resistance measurements for temperatures T = 2 − 300 K. With decreasing film thickness, i.e. decreasing sheet conductance Gs, a transition from a weakly conducting regime described by a logarithmic temperature dependence to an insulating regime occurs. In the insulating regime, the temperature dependence is described by Gs ∝ exp[−(T 0 /T) n] with an exponent n which gradually changes from 0.69 to 1 with decreasing film thickness. In contrast, for the Si(111)6 × 6-Au reconstruction obtained after annealing, an exponent n = 1/2 is found suggesting the formation of a soft Coulomb gap due to electron-electron interaction. PACS numbers: 68.37.-d, 68.55.-a, 73.50.-h, 73.25.+i,
81.15.-z