Planar aromatic anchors control the electrical conductance of gold|molecule|graphene junctions

The synthesis of a family of alkanethiol molecules with planar aromatic head groups, designed to anchor molecules effectively to graphene electrodes, is reported. Characterisation of self-assembled monolayers of these molecules on a gold surface via conductive atomic force microscopy shows that when an aromatic head group is present, the conductance G(graphene) obtained using a graphene coated probe is higher than the conductance G(Pt) obtained using a platinum (Pt) probe. For Pt probe and graphene probe junctions, the tunnelling decay constant of benzyl ether derivatives with an alkanethiol molecular backbone is determined as beta = 5.6 nm(-1) and 3.5 nm(-1), respectively. The conductance ratio G(graphene)/G(Pt) increases as the number of rings present in the aromatic head unit, n, increases. However, as the number of rings increases, the conductance path length increases because the planar head groups lie at an angle to the plane of the electrodes. This means that overall conductance decreases as n increases. Density functional theory-based charge transport calculations support these experimental findings. This study confirms that planar aromatic head groups can function as effective anchoring units for graphene electrodes in large area molecular junctions. However, the results also indicate that the size and geometry of these head groups must be considered in order to produce effective molecular designs.

Automated summary

The synthesis of alkanethiol molecules with planar aromatic head groups for anchoring molecules to graphene electrodes is investigated. The conductance of self-assembled monolayers on a gold surface shows that graphene coated probes have higher conductance than platinum probes. The study confirms the effectiveness of planar aromatic head groups as anchoring units, but highlights the importance of considering the size and geometry of these groups for molecular design.