The New Carbon Nanostructures And The Physical Properties

Low dimensional materials, especially low dimensional nano-carbon materials,have been the hot topics in the material science. Since the discovering of graphene in2004experimentally, due to its novel physical properties, much attention has beenpaid to this filed and it is predicted that the graphene would become the nextgeneration of electronic devices. The graphene can possess different properties afterdecorating. After the discovering of the graphene, a new carbon allotrope graphynehas been prepared by experimenters. Those carbon allotropes possess differentelectronic properties. As a result, much attentions has been paid to this filed (carbonallotropes). As it known to all, different carbon allotropes have different electronicproperties. In this article, we mainly paid our attentions on investigating foldedgraphene and predicting new low-dimensional carbon allotropes, hoping to providecertain theoretical help for the next generation of electronic devices. Our results list asfollows:(1) The atomic structure, stacking sequences, and electronic structure of foldedgraphene nano-ribbons (FGNRs) are investigated by the first-principles calculations.The stability of the FGNRs are associated with several factors of initial structures,such as interlayer distance of two nano-ribbons, stacking sequences, edge styles, andwidth of nano-ribbons. Interestingly, for both the two edges nano-ribbons, they canform new stacking styles instead of the most stable AB-stacking sequences (AA-,AB`-, and AB``-stacking). By calculated the energy difference between the FGNRsand GNRs, we can obtain the critical width about61and95for the zigzag andarmchair nano-ribbons, respectively.(2) A novel two-dimensional carbon allotrope rectangular graphyne (R-graphyne)is proposed by first-principles calculations. The bulk R-graphyne exhibits metallicproperty. Through different direction and widths cutting, the nano-ribbons ofR-graphyne show distinct electronic structures. Although the armchair nano-ribbonsremain the metal, the band gaps of zigzag R-graphyne nano-ribbons oscillate betweensemiconductor and metal as a function of width. Particularly, the zigzag edgenano-ribbons with half-integer repeating unit cell exhibits unexpected Dirac-likefermions in the band structures. The Dirac-like fermions of the R-graphynenano-ribbons originates from two sub-lattices and the central symmetry.(3) The low dimensional sheets of a body centered carbon bcc-C6are exploredwith first-principles calculations. Surprisingly, such low dimensional materials exhibit extraordinary physics properties. Compared to other carbon allotropes, the formationenergy and surface energy of the three face orientations [(111),(110), and (100)] arerather low, suggesting no reformation on those surfaces. Particularly, the indirect bandgap of the bulk bcc-C6becomes direct semiconductor for the2-and3-layer-(111)sheets.(4) Based on the green’s function method, the photon transport properties ofperiodic T-shaped photonic waveguide structure were investigated. It is interesting tofind that (n-1)-fold resonant splitting peak appears in low frequency area, while(n-2)-fold resonant splitting peak exists in high frequency region. The (n-1)-foldresonance peak is dominated by low quasi-bound states located in the stub. However,the (n-2)-fold resonance peak is originated from the high quasi-bound states in theconstraint. As to the photon in the high quasi-bound states, the constriction isequivalent to a potential well rather than a barrier.