Probing Lateral Charge Transport in Single Molecule Layers: How Charge is Transported Over Long Distances in Fullerene Self-Assembled Monolayers

摘要

Self-assembled monolayers (SAMs) are good candidates for electronic molecular devices as they are compatible with flexible substrates, show reliable film-forming behavior, fit well with the miniaturization concept and can be easily functionalized by changing the constituent molecular components. Most studies on the electrical properties of SAMs have focused on the conduction along the molecular axis even though this is a minor aspect of the electrical transport in SAMs as they are inherently intended to operate through lateral charge transport which instead depends strongly on intermolecular packing. Several approaches, some of which are outlined in Figure 1, have been proposed to study the lateral electrical transport in SAMs. Field-effect transistor devices in which the semiconductor channel is a single sheet of molecules formed on the gate dielectric (SAMFETs, Figure 1 a) are the most common approach and allow the charge carrier mobility to be extracted from the field-dependence of the source-drain current. In the case of SAMs formed on conductive substrates, the dependence of the domain height on the size of isolated molecular islands as measured by scanning tunneling microscopy (STM, Figure 1 b) provides an indirect assay of intermolecular charge transport between neighboring molecules. However, these techniques disagree widely on the magnitude and mechanism of charge transport in monolayers, which can range from very high mobility through ballistic charge transport to low-to-moderate mobility via percolation.