Transport properties of GNR-C60 single-molecule devices

Abstract

Based on the successful achievement of graphene-C₆₀ single-molecule transistors in experiments, a series of double-layered GNR-C₆₀, X/GNR-C₆₀ (GNR = graphene nanoribbon; X = H, O, S, passivated edge atoms) devices were designed and their transport properties investigated by means of density functional theory (DFT) and nonequilibrium Green's function (NEGF) methods. The overall conductivity followed the sequence: H/GNR-C₆₀ > S/GNR-C₆₀ > O/GNR-C₆₀, exactly opposite to the electronegativity order of O > S > H. All the X/GNR-C₆₀ (X = H, O, S) devices presented a multiple negative differential resistance (NDR) feature within the considered bias range of 0.0–1.4 V. The magnitude, position, and number of NDR peaks were remarkably influenced by the passivated edges, electrode linkages, interactions between the upper and lower GNRs, and applied voltage. C₆₀, as a medium, had a blocking action at low bias for all H/GNR-C₆₀ devices, and the NDR character originated from the crossing of the frontier molecular orbitals (FMOs), while it behaved as a conductor at high bias, and the NDR behavior was still derived from the change in FMO distributions along the scatter region. C₆₀ always acted as a blocking body in both O/GNR-C₆₀ and S/GNR-C₆₀ devices at any applied voltage, and their NDR peaks also stemmed from the crossing of the FMOs. In addition, which channel to be mainly used depended on the synergistic effect of the applied bias and connecting positions of the electrodes. All these fascinating properties suggest the materials potential applications in the field of nano-electronic devices.