Research On Transport Properties Of Nitrogen-doped Graphene Nanoribbons

Graphene have attracted enormous attention when it discovered,and many afantastic physics phenomena have found during the study.In this paper,the first-principles method based on density functional theory and non-equilibrium Green's function is used to study the electrical transport properties and possible applications of nitrogen-doped graphene.The following research results have been obtained:Edge N-doping has distinct effect on the electronic structures and transport proper-ties of the armchair GNRs and zigzag GNRs?AGNRs,ZGNRs?,due to the formation of pyridazine and pyrazole rings at the edges.The five-membered pyrazole rings at the zigzag edges destroys the magnetic edge-state,resulting in the FM and NM ground states of the single-edge and double-edge N-doped ZGNRs,respectively.The current starts to flow at zero bias,confirming the metallic characteristics.Moreover,the N-doping en-hances the conductance of the system,especially at the low bias region.Furthermore,their I–V curves are nonlinear,implying inadequate performance for use as nanowires.The six-membered pyridazine rings raise the Fermi level and introduce delocalized en-ergy bands near the Fermi level,resulting in a highly enhanced conductance in N-AGNRs at the stable nonmagnetic ground state.The single and double-edge N-doping reduces the threshold voltage from 0.4 V for the pristine AGNR to about 0.2 V and 0.0 V,respectively,confirming the important role of armchair-edge N-doping in reducing the band gap,and trans-forming the pristine AGNR from semiconducting to metallic characteristics.More-over,at each bias the current is several times larger than that of pristine AGNR,and the linear increasing voltage is accompanied by a linear increase in current in both the single and double-edge N-AGNRs.Especially for the family of AGNRs with widths of n=3p+2,their characteristics are transformed to metallic characteristics via N-doping,and they exhibit perfectly linear current–voltage behaviors.Such uniform and excellent fea-tures indicate bright application prospects of the N-AGNRs as nanowires and electrodes in molectronics.When nitrogen doping occurs in the central region of the graphene,the chemical activity of the graphene can be effectively enhanced,so that nitrogen-doped graphene perform adequately to confine Fe atoms form the FeN₄ structure.The results show that FeN₄ induces room-temperature stable ferromagnetic ground states in both AGNRs and ZGNRs.AGNRs don't have any edge states,and there is no considerable spin-split near the Fermi level of the FeN4-AGNR.The embedding of FeN4 does not introduce an impressive difference between the spin-up and spin-down systems,especially around the Fermi level.But significant changes in the electronic structure of ZGNR,inducing strong current polarization?nearly 100%?and spin-dependent negative differential resistance?NDR?in the FeN₄-ZGNR based devices.Relevant data show that the performance of the NDR can be easily enhanced by embedding more FeN₄ structures.Its peak-to-valley current ratio?PVCR?rises rapidly and reaches 10⁴when only 4 FeN₄ structures are used.It is revealed that the localized f electrons of the Fe atom and the p electrons of the C atoms at the ribbon edges have the same spin orientation,resulting in a ferromagnetic ground state with a larger magnetic moment,FeN₄ induces conductive states around the Fermi level,which are responsible for the observed NDR,and the quite different conduc-tivity of the frontier orbitals in the spin-down and spin-down systems contributes to the strong current polarization.Such intrinsic properties suggest prospective device applica-tions of the FeN4-ZGNRs in spintronics.