| Low-dimensional carbon nanomaterials have always been the focus of scientificresearch. In2004, the discovery of graphene has promoted the study oflow-dimensional carbon nanomaterials into a new round of upsurge. Especially in thefield of electronics, graphene has a lot of unique electronic transport properties andspin transport properties, which has injected new vitality into the research of newgeneration of the nanoselectronics and spin nanoelectronics. After the discovery ofgraphene, in2010another two-dimensional planar structure of lower dimensionalcarbon nanomaterial, graphyne was found by the scientists of China. In this kind ofnanostructure, there are two hybrid modes (sp and sp2). Graphyne not only has thesimilar properties to graphene, but also has excellent semiconducting properties,which graphene does not own. It creates that graphyne would have broad applicationprospects in the new generation of optoelectronic device and vacuum nanodevices.Using Green function method, we have studied the spin transport properties ofarmchair graphene nanoribbons and the electronic structures of graphyne-basedsystems in this thesis. The major results summarized as follows:(1) Using Green’s function method, we have investigated the spin transportproperties of armchair graphene nanoribbons (AGNRs) under magnetic field anduniaxial strain. Our results show that it is very difficult to transform narrow AGNRsdirectly from semiconductors to spin gapless semiconductors (SGS) by applyingmagnetic fields. However, as a uniaxial strain is exerted on the nanoribbons, theAGNRs can transform to SGS by a small magnetic field. The combination modebetween magnetic field and uniaxial strain displays a nonmonotonic arch-patternrelationship. In addition, we found that the combination mode is associated with thewidths of nanoribbons, which exhibits group behaviours.(2) We have investigated the electronic structures of graphyne nanostructures.All the graphyne-based nanostructures consist of benzene rings and acetyleniclinkages. Based on the extended Hückel theory, we fit the ab-initio energy bands ofgraphyne nanoribbons, and obtained the hopping energies:-2.60eV,-2.63eV and-3.25eV, corresponding to the benzene, single, and triple bonds, respectively. Theseparameters well reproduce the electronic structures of graphyne nanoribbonscaculated by ab-initio method, especially the band gaps. Both armchair and zigzag graphyne nanoribbons with large size have the same band gap of0.566eV, thus thegraphyne nanoribbons exhibit less anisotropic than the graphene nanoribbons. Inaddition, we have calculated the electronic structures of graphyne nanotubes, andfound that the band gaps of all nanotubes are0.566eV which is also very close to thevalue obtained by ab-initio caculation. |
