Conductive metal adatoms adsorbed on graphene nanoribbons: a first-principles study of electronic structures, magnetization and transport properties

Abstract

Using density functional theory (DFT) in combination with non-equilibrium Green's functions, we have investigated the electronic structures, magnetization, and quantum transport properties of zigzag graphene nanoribbons (ZGNRs) functionalized with conventional conductive metal adatoms (Al, Cu, Ag and Au). On the basis of the adsorption energies, our simulation demonstrates that Al and Cu adatoms are chemically bonded with ZGNRs, while the adsorptions for Ag and Au are between weak chemisorption and strong physisorption. The properties of charge transfer and magnetic moment are in reasonable agreement with the previous calculations. The adsorption of metal adatoms induce a net magnetic moment of −1 μ_B in 6ZGNR–metal systems. On the other hand, the transport studies of metal adatoms adsorbed ZGNRs suggest that the metal adatoms play an important role in the transport properties of devices and exhibit different effects on the transport properties of 6ZGNR-based and 7ZGNR-based devices. The 7ZGNR-based devices show the opposite conductive order in 6ZGNR-based devices. For 6ZGNR-based devices, the transport current in 6ZGNRs can be enhanced effectively by the adsorption of metal adatoms. However, the currents in 7ZGNR functionalized with conductive metal atoms are obviously smaller than that in pristine 7ZGNR, implying that metal adsorptions reduce the electrical conductivity of 7ZGNR-based devices. In contrast to the properties of the bulk materials, the conductivity of 6ZGNR–Al is highest among 6ZGNR–metal systems, which is in agreement with that of single atomic wires of Ag, Al, Au, and Cu.