Modifications in graphene electron states due to a deposited lattice of Au nanoparticles : density functional calculations.

We perform first-principles investigations of two-dimensional, triangular lattices of Au38 nanoparticles deposited on a graphene layer. We find that lattices of thiolate-covered nanoparticles cause electronic structure modifications in graphene such as minigaps, charge transfer, and new Dirac points, but graphene remains metallic. In contrast, for a moderate coverage of nanoparticles __0.2 nm−2_, a lattice of bare _noncovered_ Au nanoparticles may induce periodic deformations on the graphene layer leading to the opening of a band gap of a few tens of meV at the Dirac point, in such a way that a properly charged system might become a semiconductor

(issue and page numbers not yet assigned; citable using Digital Object Identifier – DOI) Original Paper The Kataura plot over broad energy and diameter ranges

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Nanoporous graphene and H?BN from BCN precursors : first-principles calculations.

We propose, based on results of first-principles calculations, that nanoporous graphene and h-BN might be efficiently produced from B?C?N layers as precursors. In our calculations, we find that the removal of the h-BN islands that naturally occur in BN-doped graphene, forming nanoporous graphene, requires less energy than if pristine graphene is used as a precursor. The same reduction ?Ef in pore formation energy is found for nanoporous h-BN obtained from graphene-doped BN as a precursor. ?Ef is found to increase linearly as a function of the number of B?C and N?C bonds at the island boundary, with the slope being nearly the same for either porous graphene or porous h-BN. This is explained by an analytical bond-energy model. In the case of porous graphene, we find that the pore formation energy would be further reduced by passivation by pyridinic and quaternary remnant nitrogen atoms at the pore edges, a mechanism that is found to be more effective than the passivation by hydrogen atoms. Both mechanisms for pore formation energy reduction should lead to a possibly efficient method for nanoporous graphene production

Vibrational G peak splitting in laterally functionalized single wall carbon nanotubes : theory and molecular dynamics simulations.

We present a theoretical study of the vibrational spectrum, in the G band region, of laterally hydrogenated single wall carbon nanotubes through molecular dynamics simulations. We find that bilateral hydrogenation e which can be induced by hydrogenation under lateral strain e causes permanent oval deformations on the nanotubes and induces the splitting of vibrational states in the G-band region. We propose that such splitting can be used as a Raman fingerprint for detecting nanotubes that have been permanently modified due to bilateral hydrogenation. In particular, our results may help to clarify the recent findings of Araujo and collaborators [Nano Lett. 12, 4110 (2012)] which have found permanent modifications in the Raman G peaks of locally compressed carbon nanotubes. We have also developed an analytical model for the proposed phenomenon that reproduces the splitting observed in the simulations

Universal deformation pathways and flexural hardening of nanoscale 2D-material standing folds.

In the present work, we use atomic force microscopy nanomanipulation of 2D-material standing folds to investigate their mechanical deformation. Using graphene, h-BN and talc nanoscale wrinkles as testbeds, universal force?strain pathways are clearly uncovered and well-accounted for by an analytical model. Such universality further enables the investigation of each fold bending stiffness ? as a function of its characteristic height h 0. We observe a more than tenfold increase of ? as h 0 increases in the 10?100 nm range, with power-law behaviors of ? versus h 0 with exponents larger than unity for the three materials. This implies anomalous scaling of the mechanical responses of nano-objects made from these materials

Graphene/h-BN in-plane heterostructures : stability and electronic and transport properties.

We present a first-principles study of structural, electronic, and transport properties of in-plane Gr:BN heterostructures in the form of graphene stripes embedded in a BN matrix. In our calculations, we consider carbon, nitrogen, and boron chemical potentials that are consistent with growth conditions (gas sources and temperatures) at either nitrogen-rich or boron-rich environments. Interestingly, we find that structures with excess of B atoms can be energetically more stable than structures with excess of N atoms even in N-rich growth conditions. The general trend is that N-rich growth conditions favor B/N stoichiometric heterostructures, while B-rich growth conditions favor heterostructures with excess of B atoms at the graphene/BN junctions, such that only B?C bonds occur at both edges of a graphene stripe region embedded in BN. We also investigate the dependence of magnetic properties and the band gap magnitudes of graphene stripe regions embedded in BN with several structural characteristics. We find that graphene stripes with only one bond type (either B?C or N?C) at the graphene/BN edges always present metallic behavior, with zigzag-oriented stripes of this type presenting large magnetic moments. Finally, we obtain the characteristic I?V curves for systems formed by junctions of two graphene stripes embedded in BN, one of them terminated by C?N bonds and the other terminated by C?B bonds. We find that systems of this type should present rectifying behavior

Graphene/h-BN heterostructures under pressure : from van der Waals to covale.

Scanning probe microscopy and ab initio calculations reveal modifications on the electronic and structural properties of graphene/h-BN heterostructures induced by compression. Using AFM and EFM techniques, with charge injection being made in the heterostructures at different pressures, the charge injection efficiency monotonically decreases with increasing pressure for monolayer-graphene (MLG)+BN heterostructures, indicative of a conductor-insulator electronic transition. Bilayer-graphene (BLG)+BN and trilayer-graphene (TLG)+BN heterostructures show a non-monotonic behavior of charge injection versus pressure, indicative of competing electronic structure modifications. First-principle calculations of these systems indicate a pressure-induced van der Waals-to-covalent interlayer transition, where such interlayer covalent binding, in the presence of water molecules, results in a disordered insulating structure for the MLG + BN case, while it leads to an ordered conducting structure for both BLG + BN and TLG + BN heterostructures. These opposing effects may have a strong influence on graphene/h-BN-based electronic devices and their physics under pressurized environments