219 research outputs found
Holey graphene: a unique structural derivative of graphene
Holey graphene (hG), also called graphene nanomesh, is a structural derivative of graphene. hG is formed by removing a large number of atoms from the graphitic plane to produce holes distributed on and through the atomic thickness of the graphene sheets. These holes, sometimes with abundant functional groups around their edges, impart properties that are uncommon to intact graphene but advantageous toward various applications. In this review, strategies to prepare hG and the related applications that take advantage of the unique structural motif of these materials are discussed. Prospects are then given for this emerging class of graphene derivatives
Electronic Structures of SiC Nanoribbons
Electronic structures of SiC nanoribbons have been studied by spin-polarized
density functional calculations. The armchair nanoribbons are nonmagnetic
semiconductor, while the zigzag nanoribbons are magnetic metal. The spin
polarization in zigzag SiC nanoribbons is originated from the unpaired
electrons localized on the ribbon edges. Interestingly, the zigzag nanoribbons
narrower than 4 nm present half-metallic behavior. Without the aid of
external field or chemical modification, the metal-free half-metallicity
predicted for narrow SiC zigzag nanoribbons opens a facile way for nanomaterial
spintronics applications.Comment: 10 pages, 5 figure
Seasonal variations in the Sr-Nd isotopic compositions of suspended particulate matter in the lower Changjiang River: Provenance and erosion constraints
Evolution of Moire Profiles from van der Waals Superstructures of Boron Nitride Nanosheets
Two-dimensional (2D) van der Waals (vdW) superstructures, or vdW solids, are formed by the precise restacking of 2D nanosheet lattices, which can lead to unique physical and electronic properties that are not available in the parent nanosheets. Moire patterns formed by the crystalline mismatch between adjacent nanosheets are the most direct features for vdW superstructures under microscopic imaging. In this article, transmission electron microscopy (TEM) observation of hexagonal Moire patterns with unusually large micrometer-sized lateral areas (up to similar to 1 mu m(2)) and periodicities (up to similar to 50 nm) from restacking of liquid exfoliated hexagonal boron nitride nanosheets (BNNSs) is reported. This observation was attributed to the long range crystallinity and the contaminant-free surfaces of these chemically inert nanosheets. Parallel-line-like Moire fringes with similarly large periodicities were also observed. The simulations and experiments unambiguously revealed that the hexagonal patterns and the parallel fringes originated from the same rotationally mismatched vdW stacking of BNNSs and can be inter-converted by simply tilting the TEM specimen following designated directions. This finding may pave the way for further structural decoding of other 2D vdW superstructure systems with more complex Moire images
Highly efficient photocatalytic degradation of dyes by a novel copper-triazolate metal-organic framework
Chemical Sharpening, Shortening, and Unzipping of Boron Nitride Nanotubes
Boron nitride nanotubes (BNNTs), the one-dimensional member of the boron nitride nanostructure family, are generally accepted to be highly inert to oxidative treatments and can only be covalently modifi ed by highly reactive species. Conversely, it is discovered that the BNNTs can be chemically dispersed and their morphology modifi ed by a relatively mild method: simply sonicating the nanotubes in aqueous ammonia solution. The dispersed nanotubes are significantly corroded, with end-caps removed, tips sharpened, and walls thinned. The sonication treatment in aqueous ammonia solution also removes amorphous BN impurities and shortened BNNTs, resembling various oxidative treatments of carbon nanotubes. Importantly, the majority of BNNTs are at least partially longitudinally cut, or "unzipped". Entangled and freestanding BN nanoribbons (BNNRs), resulting from the unzipping, are found to be approximately 5-20 nm in width and up to a few hundred nanometers in length. This is the fi rst chemical method to obtain BNNRs from BNNT unzipping. This method is not derived from known carbon nanotube unzipping strategies, but is unique to BNNTs because the use of aqueous ammonia solutions specifi cally targets the B-N bond network. This study may pave the way for convenient processing of BNNTs, previously thought to be highly inert, toward controlling their dispersion, purity, lengths, and electronic properties
Anomalous enhancement of mechanical properties in the ammonia adsorbed defective graphene
Pure graphene is known as the strongest material ever discovered. However, the unavoidable defect formation in the fabrication process renders the strength of defective graphene much lower (~14%) than that of its perfect counterpart. By means of density functional theory computations, we systematically explored the effect of gas molecules (H2, N2, NH3, CO, CO2 and O2) adsorption on the mechanical strength of perfect/defective graphene. The NH3 molecule is found to play a dominant role in enhancing the strength of defective graphene by up to ~15.6%, while other gas molecules decrease the strength of graphene with varying degrees. The remarkable strength enhancement can be interpreted by the decomposition of NH3, which saturates the dangling bond and leads to charge redistribution at the defect site. The present work provides basic information for the mechanical failure of gas-adsorbed graphene and guidance for manufacturing graphene-based electromechanical devices
Recent progress in 2D group-VA semiconductors: from theory to experiment
This review provides recent theoretical and experimental progress in the fundamental properties, electronic modulations, fabrications and applications of 2D group-VA materials.</p
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