Investigations Of Defect And Impurity Effects On The Electronic And Optical Properties Of Graphene Nanoribbons

The researchers have made great progress in silicon-based electronic devices that have been widely used in computing and other applications during the recent several decades, and the miniaturization of electronic devices is the remarkable characteristic in many aspects. In fact, the denser, more power-efficient circuitry and faster is obtained through the approach of continuously silicon-based transistors miniaturizing. Nowadays, the challenge in face of us is that the miniaturization approach will soon encounter both scientific and technical limits. It is urgent for us to make an effort to look for and develop alternative device technologies. Owing to the excellent electrical properties of the carbon-based nanomaterials, such as qusi-one-dimensional (1D) graphene nanoribbons, are considered as the ideal candidates to make next generation electronic devices. With the development of high performance cluster computers and the improvement of algorithm for calculating, computational simulations based on the first-principles are able to be performed to understand the electronic structrue of these materials and to investigate the electronic device engineering issues. More importantly, computational simulation becomes the most important theoretical method to investigate the nanoelectronics.Using the first principles based on density functional theory, the paper systematically investigates the effects of the substitutive doping, topological defect, vacancy defect and these complex defects on the electronic structures and optical properties of graphene nanoribbons, moreover, we also have explored the electronic properties of graphene nanoribbons with the adsorption of the Melamine molecule. These results is significant for the practical preparation and development of graphene nanoribbon-based electronic devices.The investigation of graphene nanoribbon with introducing Stone-Wales(SW) defect show that the symmetrical SW defect lead to the local distortion perpendicular to the plane of the graphene nanoribbon, but the asymmetrical SW defect only lead to the distortion in the plane of the graphene nanoribbon. The two SW defects arose the redistribution of the charge, it is the reason that the 7-fold ring has the negative curvature and 5-fold ring has the positive curvature. The absorption and reflectance spectrum of the graphene nanoribbon appear distinctly redshift after introducing the SW defect. The intensity of the first absorption peak of the graphene nanoribbon with symmetrical SW defect is the twice of the first absorption peak of the perfect graphene nanoribbon or the graphene nanoribbon with asymmetrical SW defect, and the first reflectance peak of the graphene nanoribbon with symmetrical SW defect is one magnitude bigger than that of the perfect graphene nanoribbon and the graphene nanoribbon with asymmetrical SW defect, it is considered that it is related with the ripple of the graphene nanoribbon with symmetrical SW defect. After taking the spin polarized into account, the calculated results show that asymmetrical SW defect affect the distribution of density of state of the different spin directions, and it appears the asymmetrical distribution at the same energy site, it is considered that the asymmetrical SW defect breaks the symmetry of the graphene nanoribbon.The paper has also made systematic simulations of graphene nanoribbon with impurity atom-vacancy (or SW defect) present contemporarily. When the boron (nitrogen)-vacancy complex defects locate on the edge of the zigzag graphene nanoribbon, these complex defects have changed the electronic and optical properties of the graphene nanoribbons distinctly. According to the band structures of these complex configurations, the presence of complex defect doesn't change the metallic character of the graphene nanoribbon. The first absorption peak of the graphene nanoribbon with boron-vacancy complex defect on the edge of the graphene nanoribbon appears blueshift compared with the graphene nanoribbon with only one vacancy. And the first absorption peak of the graphene nanoribbon with one nitrogen atom doping on the edge appears redshift compared with the graphene nanoribbon with only one vacancy, but other nitrogen-vacancy complex configurations appear blueshift.The geometry structure of the graphene nanoribbon with silicon substitutional doping on the SW defect has more changes among the graphene nanoribbons with boron (nitrogen or silicon)-SW complex defects, it is considered that it is related to larger silicon atomic radius. These complex defects affect the electronic and optical properties of the graphene nanoribbons. The boron (nitrogen)-vacancy complex defects near the edge of the graphene nanoribbon affect the geometry and electronic structures of the graphene nanoribbon distinctly. it may supply the theoretical reference for the investigation of electronic transport and the design of electronic device of the graphene nanoribbons.Doping positions regulate the electronic structure among the graphene nanoribbons with boron/nitrogen codoping. The investigation results exhibit both semiconducting and half-metallic behavior in response to the boron/nitrogen co-doping at different sites without an applied electronic field. The zigzag graphene nanoribbons with different widths have this character. It supplies the theoretical reference for the design of spin electronic devices.The investigation results of the interaction of Melamine molecule with both defected and defect free graphene nanoribbons show that the Melamine molecules are rather strongly bound to the graphene nanoribbon. It can also be found that Melamine molecules prefer to be adsorbed on Si-doped graphene nanoribbon compared with other configurations. And the band structures of the interaction of Melamine molecule with Si-doped graphene nanoribbon are different from other configurations, which is in accordance with the Mulliken analyses.In the end, the changes of the geometry and electronic band structures of the armchair graphene nanoribbons with vacancy, SW defect, dopant and complex defects are mainly discussed. The calculated results show that the different kinds of defect and dopant affect the geometry structure and electronic properties distinctly. It supplies the theoretical reference for the investigation of electronic transport and the design of electronic devices based on the armchair graphene nanoribbons.