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      Graphene Edge from Armchair to Zigzag: The Origins of Nanotube Chirality?

      , ,
      Physical Review Letters
      American Physical Society (APS)

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          Abstract

          The energy of an arbitrary graphene edge, from armchair (A) to zigzag (Z) orientation, is derived in analytical form. It contains a "chemical phase shift" determined by the chemical conditions at the edge. Direct atomistic computations support the universal nature of the relationship, definitive for graphene formation, and shapes of the voids or ribbons. It has further profound implications for nanotube chirality selection and possibly control by chemical means, at the nucleation stage.

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          Most cited references21

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          Half-metallic graphene nanoribbons.

          Electrical current can be completely spin polarized in a class of materials known as half-metals, as a result of the coexistence of metallic nature for electrons with one spin orientation and insulating nature for electrons with the other. Such asymmetric electronic states for the different spins have been predicted for some ferromagnetic metals--for example, the Heusler compounds--and were first observed in a manganese perovskite. In view of the potential for use of this property in realizing spin-based electronics, substantial efforts have been made to search for half-metallic materials. However, organic materials have hardly been investigated in this context even though carbon-based nanostructures hold significant promise for future electronic devices. Here we predict half-metallicity in nanometre-scale graphene ribbons by using first-principles calculations. We show that this phenomenon is realizable if in-plane homogeneous electric fields are applied across the zigzag-shaped edges of the graphene nanoribbons, and that their magnetic properties can be controlled by the external electric fields. The results are not only of scientific interest in the interplay between electric fields and electronic spin degree of freedom in solids but may also open a new path to explore spintronics at the nanometre scale, based on graphene.
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            Some Theorems on the Free Energies of Crystal Surfaces

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              The influence of edge structure on the electronic properties of graphene quantum dots and nanoribbons.

              Graphene shows promise as a future material for nanoelectronics owing to its compatibility with industry-standard lithographic processing, electron mobilities up to 150 times greater than Si and a thermal conductivity twice that of diamond. The electronic structure of graphene nanoribbons (GNRs) and quantum dots (GQDs) has been predicted to depend sensitively on the crystallographic orientation of their edges; however, the influence of edge structure has not been verified experimentally. Here, we use tunnelling spectroscopy to show that the electronic structure of GNRs and GQDs with 2-20 nm lateral dimensions varies on the basis of the graphene edge lattice symmetry. Predominantly zigzag-edge GQDs with 7-8 nm average dimensions are metallic owing to the presence of zigzag edge states. GNRs with a higher fraction of zigzag edges exhibit a smaller energy gap than a predominantly armchair-edge ribbon of similar width, and the magnitudes of the measured GNR energy gaps agree with recent theoretical calculations.
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                Author and article information

                Journal
                PRLTAO
                Physical Review Letters
                Phys. Rev. Lett.
                American Physical Society (APS)
                0031-9007
                1079-7114
                December 2010
                December 3 2010
                : 105
                : 23
                Article
                10.1103/PhysRevLett.105.235502
                21231478
                bde7eb35-db96-4ac7-a695-3ca58fbc4a5e
                © 2010

                http://link.aps.org/licenses/aps-default-license


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