A first-principles study on transport properties of polyacene in zigzag graphene nanoribbon: Configuration, length and doping effects

Abstract

Electronic transport properties of molecular junctions constructed by bridging a polyacene (PA) molecule between two zigzag graphene nanoribbons (ZGNR) are studied based on density functional theory and the nonequilibrium Green function method. It is found that the molecule-electrode coupling strength is related to the PA position with respect to the nanoribbon edge, which gives rise to the configuration dependency of transport properties. Negative differential resistance (NDR) is predicted in the junctions of which the PA molecule aligns with the inner part of the ZGNR. The on-set bias and current peak decrease as the PA molecule moves inward. The origin of NDR is presented by analyzing the transmission spectra, relative voltage-drop rate, and electron density difference of the junctions. The on-set bias is proportional to the energy of the resonance peak of the lowest unoccupied molecular orbital and can be tuned by the PA molecule length or by doping. This work provides a detailed discussion on PA-bridged ZGNR junctions, which may help to understand ZGNR-based molecular junctions and design negative differential resistance devices.