Bias Dependence of Rectifying Direction in a Diblock Co-oligomer Molecule with Graphene Nanoribbon Electrodes

Abstract

By applying nonequilibrium Green’s function method in combination with density functional theory, we study the rectifying properties of dipyrimidinyl-diphenyl co-oligomer molecules embedded in a carbon atomic chain sandwiched between two graphene nanoribbon (GNR) electrodes. Both the length of the carbon atomic chains and the edge geometry of the graphene nanoribbon electrodes are shown to play a significant role in determining the conductance behavior and rectifying performance of the molecular devices. As for GNRs with zigzag edges, the parallel (perpendicular) conformation between the principal plane of the molecule and the zigzag-edged GNR electrode is observed to be dependent on the odd (even) number of carbon atoms in the carbon chain, whereas for armchair-edged GNRs the parallel (perpendicular) case corresponds to an even (odd) number of carbon atoms. Taking an asymmetric arrangement of armchair and zigzag GNR electrodes, we demonstrate a molecular device having very interesting rectifying behaviors with marked rectification ratios at low bias voltages and inversion of rectifying direction when the bias voltage is large. Analysis of the transmission coefficients and molecular projected self-consistent Hamiltonian as well as band structures of the electrodes under various external bias voltages reveals an underlying mechanism of the observed results.