Graphene-Contacted Single Molecular Junctions with Conjugated Molecular Wires

In this study, we have determined the electrical properties of amine- and thiol-terminated poly(p-phenylene) molecular wires bound either between two gold electrode contacts (Au/Au) or between a gold contact and a graphene electrode (Au/graphene). These different junctions were studied using a scanning tunneling microscopy (STM) and a noncontact method for forming the molecular bridges (the I(s) technique, where I = current and s = distance). We show that for these molecular targets, junctions formed with Au/Au electrodes have higher conductance than those formed with Au/graphene electrodes. The measured conductance decays exponentially with an increase in the number of phenyl rings, giving a decay constant that is similar for amine- and thiol-terminated molecular junctions with the Au/graphene system. This work reveals that poly(p-phenylene) chains present similar electronic properties when coupled to either gold or graphene electrodes, independently of whether the anchoring group is amine or thiol(ate), and that the transport properties are essentially dominated by the intrinsic molecular properties.