Electronic Transport Properties Of Graphene(ZGNRs)/Metal Planar Junction

Graphene and graphene nanoribbons(GNRs) have great potential applications in thefield of nanoelectronics due to the excellent electronic properties. In this paper, we studythe electronic transport properties of graphene/metal and ZGNRs/Ni planar junction byusing the density functional theory in combination with nonequilibrium Green’s function,the main works as follows:(1) We have studied the electronic transport properties of graphene/Ni(111) planarjunction. When graphene adsorbs on the Ni(111) surface, there are two most stablesymmetric configurations, namely bridge-top and top-fcc. We find that the transmissionof the graphene/Ni system presents spin polarization due to the strong interaction betweengraphene and the Ni substrate. By analyzing the work function difference and the densityof states of the left and right electrodes on two-probe device, we find that the transportproperties of the device depend on the electronic states of carbon atoms on the planarjunction around Fermi level. The spin splitting occurs on the transmission valley valuebelow the Fermi level, which is mostly induced by the spin splitting of the electronicstates of graphene on the scatting region and right electrode when the present of theinteraction between graphene and the edge of the Ni electrode. Moreover, for thebridge-top adsorption structure, there is a relative larger fluctuation Coulomb potential atthe contact area of the two-probe system, which is the main reason for the present of thesmall transmission gap.(2) We have studied the influence of metal substrate on the electronic transportproperties of the two-probe device by the physical absorption of graphene on the differentsubstrates of Au, Ag, Al and Cu. Two transmission minima(tm) appear in the transmissionspectra for all four types of metal planar junctions. The transmission minima of thedevices, especially asymmetric differential conductance under opposite bias, aredetermined by not only the mismatch of the work function between clamped andfreestanding region but also the electrostatic potential around the junction.(3) We have studied the most stable adsorption structures of ZGNRs with differentsymmetries on the Ni(111) substrate and the electronic transport properties of ZGNRs/Niplanar junction. Owing to the edge state of ZGNRs, there are strong coupling effectbetween ZGNRs and the Ni(111) electrode which results in the transition of ZGNRs fromthe antiferromagnetic semiconductor to the spin-polarized materials. Moreover, we findthat the ZGNRs absorbed on Ni(111) presents the spin polarization of47%. It appears a transmission gap near the Fermi level which is derived from the local effective potentialof the two-probe device. Meanwhile, ZGNRs/Ni planar junction exhibits a spin filtrationefficiency of100%near the state of the highest occupied molecular orbital.