| Graphene, a two-dimensional honeycomb crystal consisting of carbon atoms, has unusual and interesting properties. It is considered to be a new material with new physics, and it is supposed to cause major breakthrough in nanotechnology. Recently, the electronic properties of graphene have attracted great interest both theoretically and experimentally. Owing to the rapid development of scientific computation, computer softwares based on first-principles have become an important method to investigate the properties of graphene. In this thesis, the electronic and magnetic properties of graphene have been investigated by using Vienna Ab-initio Software Package (VASP) based on density functional theory. First, the electronic and magnetic properties of both non-hydrogenated and hydrogenated curved zigzag graphene nanoribbons (ZGNRs) have been studied. And then, the effects of uniaxial strains, vacancy defects and doping on curved ZGNRs have also been studied. Finally, the electronic and magnetic properties of ZGNRs and armchair graphene nanoribbons (AGNRs) co-doped by boron (B) and nitrogen (N) have been investigated. The specific research contents and results are as follows:(1) Non-hydrogenated ZGNR11 and ZGNR12 models and hydrogenated ZGNR11H and ZGNR12H models have been studied. It is revealed that hydrogenated models are more stable than non-hydrogenated models, and that planar structures are more stable than curved structures. In addition, all the models with different curvatures generate spin polarization. The dangling bonds of edge carbon atoms, especially P orbit of edge carbon atoms will impact the spin polarization of the non-hydrogenated models obviously. However, the spin polarization of hydrogenated models without dangling bonds is weaker. Uniaxial strains have been applied on the ZGNR11 and ZGNR11H models. ZGNR11H models are not sensitive to the strain, while the band structures of non-hydrogenated ZGNR11SW06 are mainly influenced by compressive and tensile strains. Vacancy defects can enhance the spin polarization of ZGNR11H models. The models with single vacancy defect have larger magnetic moment than that with divacancies defect, and the carbon atoms around vacancy defect make the greatest contribution to the spin polarization. It is found that the electronic and magnetic properties of ZGNR11H models can be changed by doping B and N. The spin polarization of ZGNR11H models will enhance after being doped by B and N.(2) The electronic and magnetic properties of ZGNRs with one-side and two-side edge doping have been studied. It is shown that after being doped by B and N, ZGNRs have stronger spin polarization and larger magnetic moment than the non-hydrogenated models. The spin polarization of one-side-doped model is more obvious than that of two-side-doped model. It is also shown that after being doped by B and N horizontally, ZGNRs have stronger spin polarization and larger magnetic moment than the non-hydrogenated models. The spin polarization and magnetic moment of models change with the increasing number of BN (B and N) chains. ZGNR11C2BN1, doped by one BN chain, has most obvious spin polarization and maximal magnetic moment. Zigzag boron and nitrogen nanoribbons, composed of B and N atoms, is a semiconductor and has large magnetic moment. It can be used as spintronic devices in the future.(3) The electronic and magnetic properties of AGNRs with one-side and two-side edge doping have been studied. The spin polarization of both non-hydrogenated and edge doped AGNRs are very weak, and all the models have no magnetism. AGNR10C1BN2, horizontally doped by two BN chains, has generated spin polarization. AGNR10C2BN1, horizontally doped by one BN chain, has generated no spin polarization. However, AGNR10C2BN1 has indirect band gap and is a p-type semiconductor. The electronic and magnetic properties of AGNR10 can be changed by doping BN chains. AGNR10 can be changed from metal to semiconductor or insulator by doping BN chains. It can be used as spintronic devices in the future. |
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