First-Principles Study On The Electronic Structure And Magnetism Of Nonmetallic Atom-Doped Graphene Nanoribbons

Based on the first-principles method of density functional theory(DFT),this thesis studies the electronic structure and magnetic properties of graphene nanoribbons(GNR)substituted by nonmetallic atoms.The main findings are as follows:Firstly,the electronic structure and magnetism of the armchair-edged graphene nanoribbon(AGNR)and zigzag-edged graphene nanoribbon(ZGNR)are studied when different nitrogen atomic numbers are doped around single-and double-vacancy defects.After systematic research,it was found that when nitrogen atoms were doped around the AGNR single-vacancy defect,only the structure with dangling bond would have a magnetic moment.When nitrogen atoms were doped around the double-vacancy defect,the generation of magnetic moment is related to the number of carbon atoms with dangling bonds in the structure,and the magnetic moment generated by the structure is always an integer.The doping of nitrogen atoms around the single-vacancy defect in ZGNR will change the magnetic magnitude of the structure,while the double-vacancy defect system shows different characteristics with the parity of the number of nitrogen atoms doped,and does not induce magnetism when it is even,and magnetism when it is odd,the magnetic moment is 5μ_B.The analysis shows that the fundamental reason is that the odd number of doped nitrogen atoms causes the system to reverse from the antiferromagnetic state to the ferromagnetic ground state.Therefore,the electronic structure and magnetism of graphene nanoribbons can be regulated by controlling the doping number of nitrogen atoms.Secondly,the effects of doping of nitrogen and phosphorus pairs at different positions and concentrations on armchair-edged graphene nanoribbons with width 7(7AGNR)are studied.It was found that the position and concentration of nitrogen and phosphorus atom pairs doped have an effect on the electronic structure and magnetism of7AGNR.When the nitrogen atom pair doping concentration is low and the doping position is in the center of the nanoribbon,the addition of twoπelectrons causes a change in the ground state of the structure,and the electronic structure and magnetism also change significantly,inducing a magnetic moment of 2μ_B.Pairs of phosphorus atoms only induce magnetism when the doping concentration is low and the two phosphorus atoms are in adjacent positions.Finally,the magnetic properties of the substituting doped system at the edge of7/9AGNR were studied.Boron atom and nitrogen atom doping of 7AGNR subband edges with trivial topologies,9AGNR subband edges with non-trivial topology,and the entire graphene nanoribbon edge have obvious effects on the electronic structure of 7/9AGNR:When the single edge is doped,boron and nitrogen atoms can induce magnetism when doped separately in the 7AGNR and 9AGNR subbands,but the edge doping of the entire nanoribbon does not induce magnetism.In double-edge doping,boron is doped at the edge of the topological non-trivial 9AGNR subband to induce magnetism and has a magnetic moment of 2μ_B,twice that of single-edge doping.In the 7AGNR subband with a mediocre topology,the double-edge doped magnetic moments cancel each other out,and the behavior is non-magnetic.Therefore,in the future,nanoribbon magnetism can be effectively modulated by different types of edge doping of topological graphene nanoribbons.In conclusion,several methods for non-metallic atom doping to generate magnetic and stable magnetic moments from graphene nanoribbons are studied.It provides certain theoretical support for exploring the introduction of stable high magnetism into graphene nanoribbons.