α-graphdiyne--a Novel Carbon Allotrope:First-principles Studies

Graphene has ignited theoretical prediction and intense search for two-dimensional materials and their qusi-one-dimensional counterparts such as nanorib-bons, single-and multi-walled nanotubes, which is due to its unique electronic proper-ties. To understand the underlying physics and subsequently how to design new related materials, as well as how to extend their potential applacations in nanoelectronics are the focus of future research. Before the realistic preparation in experiments, it is nec-essary to take simulations on those novel materials.In this thesis, we predict a new carbon allotrope called a-graphdiyne through using first-principles calculations within the framework of density functional theory (DFT). Such a-graphdiyne is a direct derivative from graphene in which two acetylenic (-C=C-) linkages are inserted in each carbon bond of graphene. First, Dirac cones and points are thoroughly studied. But the absence of band gap in a-graphdiyne limits its use in nanoelectronics. Therefore, we resort to the nanoribbon structured a-graphdiyne for the next part. In addition, we investigate the nanotubes of α-graphdiyne and find that the electronic structures can be tunable under these nanostructured functionaliza-tion. Finally, p-and n-doped a-graphdiyne nanoribbons are investigated, demonstrat-ing tunable electronic structures. We believe the work like ours should provide a good guide to experiments. The main findings of our work are as follows:(1) We systematically investigate a-graphdiyne through using first-principles within the framework of DFT, indicating a-graphdiyne possesses electronic properties similar to/better than graphene. The optimized configuration is ob-tained, showing a-graphdiyne renders the hexagonal lattice of graphene. α-graphdiyne is expected to be experimentally synthesized on Si(111) surface as the tiny mismatch between them. Band structures show that a-graphdiyne ex-hibits similar Dirac points and cones to graphene. Further, the tight-binding method is used to exploit the linear dispersion in the vicinity of Dirac points. Thanks to the larger lattice constant, a-graphdiyne yields a lower Fermi veloc-ity, which might make itself an ideal material to serve the anomalous integer quantum Hall effect, nanoelectronics and hydrogen storage.(2) The absence of band gap in a-graphdiyne significantly limits its practical appli-cations. To this end, we resort to the nanoribbon structured a-graphdiyne. This is a conventional proposal to open up the energy gaps in nanomaterials. The re-sults show that both the armchair and the zigzag α-graphdiyne nanoribbons do generate energy gaps, which are width-dependent. In addition, the underlying mechanism of this opening is explored. The former is ascribed to the combina-tion of quantum confinement and edges’effect, while the latter arises from the edge magnetic ordering. These novel nanoribbons with opening energy gaps would be potentially used in electronic devices.(3) a-graphdiyne-based nanotubes have excellently mechanic and electronic prop-erties, which are due to the lager lattice constant compared to graphene nan-otubes. At the same time, this loose geometric configuration will introduce some superior characteristics which by contrast are absent in graphene nan-otubes. The first-principles calculations show that the armchair a-graphdiyne nanotubes are metallic, while the zigzag ones are semiconductors when the chirality number n≠3p with p being integers. Our results give rising the opportunity of building nanoscaled electronic devices based on nanotubes.(4) The electronic and magnetic properties of boron and nitrogen-doped a-graphdiyne nanoribbons have been studied. For zigzag configuration, both boron and nitrogen dopants can tune the electronic properties of nanoribbons, including the introduction of spin-polarized defect states and the tunability of band gap.