The Electronic Structure And Optical Properties Of Impure Graphene Nanoribbons

Nanometric carbon materials exhibit various remarkable properties because of thegeometry of their structures. Among them, graphene nanoribbons are nanometer-sizedstrips of single-layer graphene, which have recently been the focus of extensiveexperimental and theoretical efforts. Due to the excellent electrical properties of thequsi-one-dimensional graphene nanoribbons, graphene nanoribbons are considered asthe ideal candidates to make next generation electric devices.Using the first principles based on density functional theory, the papersystematically investigates the substitutive doping of boron or nitrogen, and thecomplex defects of vacancy and doping on the electronic structures and opticalproperties of graphene nanoribbons. We get some available results which aresignificant for the practical preparation and development of the graphenenanoribbons-based photoelectric devices.We have studied electronic structure and optical properties of boron or nitrogensubstitutive doped graphene nanoribbons with zigzag edges. The graphenenanoribbons still keep its metallic character when substitutive doping boron ornitrogen. Our calculation indicates that the most energy-favorable site of boron ornitrogen doping is at the edge of the graphene nanoribbons. The electronic structuresare different from those of boron-doped or nitrogen-doped carbon nanotubes. Fornitrogen doping carbon nanotubes, there is a striking impurity level falling near thebottom of the conduction band. However, for nitrogen doping graphene nanoribbonsthe donor level is not the impurity level. The impurity level is autoionzed so that therelevant charge carrier occupies the conduction band. The donor level comes from thesubbandβof the conduction band’s bottom, while the impurity level comes from thesubband α. The electronic structures of boron-doped graphene nanoribbons arecontrary to those of nitrogen-doped. For boron-doped graphene nanoribbons theacceptor level coms from the subband γand the impurity level comes from thesubbandδ. For boron-doped or nitrogen-doped graphene nanoribbons, a remarkableimpurity level appears in the conduction band or valece band, owing to a complicatedhybridization takes place with the unoccupied bands or occupied bands. Because ofboron or nitrogen doping, the charge densities of the graphene appear theredistribution. More ever, there is a evident impurity absorption peak or reflection peak in the absorption spectrum or reflection spectrum.The paper also investigates the electronic structures and optical properties ofgraphene nanoribbons with complex defects. The calculation indicates that there is alarge effect on geometry structure due to one vacancy is at the edge of graphenenanoribbons. We find two carbon atoms out of the two-dimensional plane. Thecomplex defects significantly change the graphene nanoribbons’s electronic structure,at the same time, they have a remarkable effect on the charge densities near thecomplex defects, while there are almost no change out of the complex defects.Complex defects especially vacancy and boron nitrogen co-doping structures willappear a clear impurity absorption peak in the low energy area.It is one of the most promiseful methods for application to modulate the propertiesof graphene nanoribbons by impurity doping and defects. Therefore it is an importantsubject to investigate the properties and the device fabrication of doped graphenenanoribbons more deeply and comprehensively.