We report optical properties of the smallest single-walled carbon nanotubes (SWNTs) with a diameter of only 3 A. These ultrasmall SWNTs are fabricated in the elliptical nanochannels of an AlPO-11 (AEL) single crystal. Polarized and resonant Raman scattering unambiguously revealed that these 0.3 nm SWNTs are of (2,2) armchair symmetry. Interestingly, the (2,2) armchair tube has two metastable gr...

Based on a first-principles approach, we present scaling rules for the band gaps of graphene nanoribbons (GNRs) as a function of their widths. The GNRs considered have either armchair or zigzag shaped edges on both sides with hydrogen passivation. Both varieties of ribbons are shown to have band gaps. This differs from the results of simple tight-binding calculations or solutions of the Dirac's...

Materials of the general form MX2 (transition metal dichalcogenides) have generated a lot of interest recently. They can form nanoribbons like graphene and such nanoribbons have versatile electronic structures and can be metallic or semiconducting by changing the edges of the ribbon. The electronic properties of such materials are not fully understood till now. In this paper we investigate one ...

For the single-wall carbon nanotubes conducting in the simplest tight binding model, the complete set of line group symmetry based quantum numbers for the bands crossing at Fermi level are given. Besides linear (k), helical (k̃ and angular momenta, emerging from roto-translational symmetries, the parities of U axis and (in the zig-zag and armchair cases only) mirror planes appear in the assignat...

Single-walled boron nitride nanotubes are chosen as model reactants, and (10,0) and (6,6) are chosen as representatives of armchair and zigzag nanotubes, respectively, to study the interaction of carbenes of the type :CX2. It is found that, contrary to the case of carbon nanotubes, boron nitride tubes, particularly armchair BNNTs, do not show a propensity for cyclopropane ring formation. The SW...

Confocal Raman spectroscopy is used to study the phonon modes of mechanically exfoliated single-layer graphene sheets in ambient air. We observe that ambient gas induces obvious shifts in the G band frequency as well as the change in intensity ratio of 2D and G bands, I(2D)/I(G), owing to the Fermi energy change by ambient gas doping. The change in I(2D)/I(G) for the armchair edge is significan...

The colors of suspended metallic colloidal particles are determined by their size-dependent plasma resonance, while those of semiconducting colloidal particles are determined by their size-dependent band gap. Here, we present a novel case for armchair carbon nanotubes, suspended in aqueous medium, for which the color depends on their size-dependent excitonic resonance, even though the individua...