From fused aromatics to graphene-like nanoribbons: The effects of multiple terminal groups, length and symmetric pathways on charge transport

Abstract

A class of molecular ribbons, with almost-ideal charge transmission, that is weakly dependent on the anchoring structure or electrode crystalline orientation and easy to synthesize has been identified. Charge transport through two sets of aromatic nanoribbons, based on the pyrene and perylene motifs, has been investigated using density functional theory combined with the nonequilibrium Green's function method. The effects of wire length and multiple terminal thiolate groups at the junction with gold leads have been examined. For the oligopyrene series, an exponential drop in the conductance with the increase of the wire length is found. In contrast, the oligoperylene series of nanoribbons, with dual thiolate groups, exhibits no visible length dependence, indicating that the contacts are the principal source of the resistance. Between the Au(001) leads, the transmission spectra of the oligoperylenes display a continuum of highly conducting channels and the resulting conductance is nearly independent of the bias. The predictions are robust against artefacts from the exchange-correlation potential, as evidenced from the self-interaction corrected calculations. Therefore, oligoperylene nanoribbons show the potential to be the almost-ideal wires for molecular circuitry.

Anomalous length dependence of conductance of aromatic nanoribbons with amine anchoring groups

“…Low bias conductance exhibits the familiar exponential decay with the length of wire. 28 An attenuation factor β of 0.34Å −1 is obtained for this series, in reasonably good agreement with 0.25 1 and 0.38 28 previously evaluated for their counterparts with thiol head groups anchored to the Au(111) surface. The exponential decay of the conductance with the wire length, commonly observed for amine terminated molecules, [5][6][7] is consistent with the nonresonant tunneling mechanism or superexchange.…”

“…This is also in contrast with the results for the same, but thiol terminated nanoribbons, which demonstrate nearly length-independent conductance. 1 The same plot also shows the effect of coordination by dual adjacent Au adatoms on the conductance of 2R. The corresponding current is only about 10%-15% higher than that when single adatoms are employed.…”

“…[25][26][27] This binding site selectivity reduces the relevance of the choice of the underlying crystalline orientation of the terminals. Hence, unlike in the case of thiolate terminated nanoribbons, 1 it can be assumed that the present results equally apply to gold (111) terminals. The oligopyrene wires have been connected to the terminals by attaching the amine groups to the single adatoms on the opposite ends of the junction.…”

“…1 A N pseudopotential of Troullier and Martins type, 11 with a partial core correction, has been generated using the parameters available from URL http://www.eminerals.org/siesta. Geometry optimizations were performed using density functional theory (DFT) as implemented in the SIESTA program.…”

“…1 The findings of a consistently high conductance, nearly independent of the anchoring structure, gold lead crystalline orientation, wire length, and bias voltage, makes the oligoperylene nanoribbons almost ideal wires for molecular circuitry. The thiol terminal groups, commonly utilized for the attachment of organic molecules to gold surfaces, provide a very strong bond with the leads.…”