The Effect On Transport Properties Of Zigzag Graphene Nanoribbion With Doping, Defect And Edge Modulation

Owing to the remarkable geometry structural and electrical properties and large potential applications in nanoelectronic devices, graphene nanoribbons (GNRs) have attracted vast attention. By using the first-principles methods within the framework of density functional theory and Nonequilibrium Green's functions method, we study the eletronic structures and transport properties of zigzag graphene nanoribbon (ZGNRs) with doping, defect, and edge modulation. The results are summarized as follows:(1) The effect of multivacancies defects and defect edge impurities on the electronic structures and transport properties of ZGNRs is investigated. The results show that the ZGNRs with multivacancies defects and B/N pairs doping display metallic behavior. The transport properties of the defect ZGNRs can be tuned by using change the doping type. Under the low bias, the current of the ZGNRs with multivacancies defects and defect edge impurities obviously decrease, leading to the negative differential resistance (NDR) behavior. The negative differential resistance is caused by the effect of coupling between frontier molecule orbits and electrode.(2) Under different spin configuration, the effect of hydrogenation at the nanoribbons on the electronic transport properties of ZGNRs with different symmetry is studied. It is found that for the ferromagnetic (FM) state the symmetry and asymmetry ZGNRs with one edge terminated with single hydrogen atom and the other edge terminated with two hydrogen atom show spin diode effect due to SP3hybrid of one edge, and that in the antiferromagnetic (AF) state the symmetric ZGNRs show the spin filter effect due to the broken magnetism symmetric of ZGNRs with the edge defectes. In addition, the ZGNRs isomers with asymmetry hydrogenation at two sides show a means of one-way transmission.(3) The transport properties of ZGNRs terminated with three kinds of3d metal atoms such as Fe, Co, and Ni are investigated. The results show that the electronic transport properties of doping ZGNRs are depending on the type of terminated atom at the edge of ribbon. The introduction of3d metal atom causes the decrease of current in the doping ZGNRs, and ZGNRs with Fe doping show the spin-filter effect. The NDR behavior appears in the ZGNRs with Ni doping. These phenomena are relevant to electron resonance reflection at the edge states and based on the electronic properties of magnetic atoms at the edge of ribbon.(4) The spin transport properties of heterojunction based on the ZGNRs with different electrical properties are studied. Firstly, the heterojunction made up of boron atoms doping ZGNRs and nitrogen atoms doping ZGNRs is studied. It is found that asymmetry doping at the ribbon edge causes the the spin polarization effect, leading to the current split of two spins, and that under the AF state the heterojunction with symmetry doping shows the one direction conductivity and P-N junction effect. Secondly, the transport properties of the heterojunction constructed with ZBNNR and ZGNR is investigated. The results show that for the AF state the heterojunction exhibits semiconductor behavior and diplays the spin-filter effect under the positive bias. In addition, the obvious rectifier effect and giant magnetic impedance effect appear in the heterojunction. The reseach provides ideas for the design of nanoelectronics and spintronic devices based on GNRs.