Electrical transport through ultrathin ordered K3C60 films on Si Original Research Article

The electronic transport properties of K-doped C60 mono- and multi-layers are reported with focus on the superconducting transition. The films were deposited on the 7×7 reconstructed Si(111) surface in UHV and showed a well-ordered growth structure. We have measured the electrical resistivity of films with thicknesses between 1 and 6.5 monolayers (ML) in a four-probe arrangement. All films show a semiconducting temperature dependence of the resistivity even though they are doped with 3 K atoms per C60. Nevertheless, we find a transition to a superconducting state for films as thin as 2.4 ML. Normal and superconducting properties are discussed in the context of disorder and film thickness.