Navegando por Autor "Ferreira, Mauro S."
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Artigo Bandgap oscillation in quasiperiodic carbon-BN nanoribbons(Elsevier, 2014-02) Pedreira, Danilo Oliveira; Azevedo, Sérgio; Bezerra, Claudionor Gomes; Viol, Aline; Viswanathan, Gandhimohan M.; Ferreira, Mauro S.In this work we address the effects of quasiperiodic disorder on the physical properties of nanoribbons, composed by BN and C, constructed according to the Fibonacci quasiperiodic sequence. We assume BN and C as the building blocks of the resulting quasiperiodic structure. The density of states and energy band gap were obtained through ab-initio calculations based on the density functional theory. We report the effects of the quasiperiodic disorder on the oscillatory behavior of the specific heat, in the low temperature regime, and on the behavior of the energy band gap. In particular, we show that the electronic energy band gap oscillates as a function of the Fibonacci generation index n. Our results suggest that the choice of the building block materials of the quasiperiodic sequence, with appropriate band gap energies, may lead to a tuneable band gap of quasiperiodic nanoribbonsArtigo Sublattice imbalance of substitutionally doped nitrogen in graphene(Elsevier, 2014-10) Lawlor, James A.; Gorman, Paul D.; Power, Stephen R.; Bezerra, Claudionor Gomes; Ferreira, Mauro S.Motivated by the recently observed sublattice asymmetry of substitutional nitrogen impurities in CVD grown graphene, we show, in a mathematically transparent manner, that oscillations in the local density of states driven by the presence of substitutional impurities are responsible for breaking the sublattice symmetry. While these oscillations are normally averaged out in the case of randomly dispersed impurities, in graphene they have either the same, or very nearly the same, periodicity as the lattice. As a result, the total interaction energy of randomly distributed impurities embedded in the conduction-electron-filled medium does not vanish and is lowered when their configuration is sublattice-asymmetric. We also identify the presence of a critical concentration of nitrogen above which one should expect the sublattice asymmetry to disappear. This feature is not particular to nitrogen dopants, but should be present in other impurities