Tailoring single-molecule conductance with structured graphene electrodes

Abstract

Modulation of electric currents through single-molecule junctions is usually achieved by synthesis of molecules with desired functionalities, in conjunction with suitable molecule–electrode contacts through specific anchoring groups. An alternative to this approach, barely explored so far, is to use structured electrodes, where conductivity could eventually be controlled by changing the specific anchoring site within the very same electrode. Here, we theoretically investigate how to exploit the pronounced anisotropy of corrugated graphene deposited on Ru(0001) (Gr/Ru) to tailor single-molecule conductivity in 4-aminophenyl and 4-aminobenzonitrile. We show that currents induced in the upper and lower anchoring positions in the Gr/Ru moiré are substantially different, irrespective of the chosen molecule. The magnitude of these currents can differ by as much as an order of magnitude at specific bias voltages. We also show that both molecules display rectifying properties, which can differ by up to a factor of five in different anchoring sites. Interestingly, the observed modulations strongly depend on the chemical binding nature between the molecule and the electrode, (strong) covalent bond for 4-aminophenyl and (weak) physisorption for 4-aminobenzonitrile. All this suggests that Gr/Ru can be an ideal electrode to modulate single-molecule electric conductivity under experimental conditions that are available in many laboratories.