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

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.

Figure 1

The 4R (pyrene dithiol) and 5R (perylene tetrathiol) wires.

Figure 2

Upper panel: Current vs bias voltage for the 1-4-7-10R series of wires between the Au(111) terminals. Lower panels: The zero-voltage transmission probability across these junctions. The energy is given relative to the Fermi level.

Figure 3

Upper panel: Current vs bias voltage for the 2-5-8-11R series of wires between the Au(111) terminals. Lower panels: The zero-voltage transmission probability across these junctions. The out-of-plane $p$ orbital contribution to the partial density of states (PDOS) from an edge C atom is also shown for the 2R and 5R wires in the lower panel.

Figure 4

The geometries of hollow, $hollo{w}^{\prime }$, bridge, and bridge o-p adsorbed 1R.

Figure 5

Upper panel: Current vs bias voltage for the 1R wire in the five junction geometries between the Au(001) terminals. Lower panels: The zero-voltage transmission probability across these junctions. The energy is given relative to the Fermi level.

Figure 6

Upper panel: Current vs bias voltage for the 1-4-7-10-13R series of wires between the Au(001) terminals. Lower panels: The zero-voltage transmission probability across these junctions. The energy is given relative to the Fermi level.

Figure 7

Upper panel: Current vs bias voltage for the 2-5-8-11R series of wires between the Au(001) terminals. Lower panels: The zero-voltage transmission probability across these junctions. The out-of-plane $p$ orbital contribution to the partial density of states (PDOS) from an edge C atom is also shown for the 2R wire in the lower panels. The energy is given relative to the Fermi level.

Figure 8

Upper panels: Energy bands of the electronic states in the junctions comprising the 4R wire between the Au(111) (left) and Au(001) (right) terminals. Only the states in the vicinity of the Fermi level are shown. The dispersionless occupied state, corresponding to the HOMO in the gas phase, is highlighted in red around the zone center. Lower panels: The orbital shape of this state at the zone center in the Au(111)-based (left) and Au(001)-based (right) junctions. Only the Au atoms forming the hollow sites are shown.

Figure 9

The HOMO and LUMO energy levels for 1-4-7-10R and 2-5-8-11R series of nanoribbons calculated with siesta.

Figure 10

The shape of the electronic states with the out-of-plane $\pi$ symmetry and energy close to the Fermi level at the $\Gamma$ point for the 2R junction. The energies are given in eV, relative to the Fermi level.