Navegando por Autor "Azevedo, Sérgio"
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Artigo Bandgap oscillation in quasiperiodic (BN)xCy nanotubes(Elsevier, 2016-12) Freitas, Aliliane Almeida de; Bezerra, Claudionor Gomes; Azevedo, Sérgio; Machado, Leonardo Dantas; Pedreira, Danilo OliveiraIn the present contribution, we apply first-principles calculations to study the effects of quasiperiodic disorder on the physical properties of BN and C nanotubes. We take BN nanotubes (BNNTs) and C nanotubes (CNTs) as building blocks and construct quasiperiodic BNxCy nanotubes according to the Fibonacci sequence. We studied armchair and zigzag nanotubes of varying diameters. Our results demonstrate that the energy gap oscillates as a function of the n-generation index of the Fibonacci sequence. Moreover, we show that the choice of the BNNTs and CNTs may lead to a quasiperiodic BNxCy nanotube presenting an adjustable energy gap. We obtained a variety of quasiperiodic nanotubes with energy gaps ranging from 0.29 eV to 1.06 eV, which may be of interest for specific technological applications. Finally, it is also demonstrated that the specific heat of the quasiperiodic zigzag and armchair nanotubes presents an oscillatory behavior in the low temperature regime, and that this behavior depends on the curvature of the nanotubeArtigo 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 Stability and electronic properties of (Ge)x(BN)y monolayers(Elsevier, 2017-10) Freitas, Aliliane Almeida de; Machado, Leonardo Dantas; Tromer, Raphael Matozo; Bezerra, Claudionor Gomes; Azevedo, SérgioIn this work, we employ ab initio simulations to propose a new class of monolayers with stoichiometry (Ge)x(BN)y. These monolayers belong to a family of 2D materials combining B, N and group IV atoms, such as BxCyNz and . We calculated the formation energy for ten atomic arrangements, and found that it increases when the number of BGe and NGe bonds increases, and decreases when the number of BN and GeGe bonds increases. We found that the lowest energy monolayer presented a stoichiometry, and maximized the number of BN and GeGe bonds. This structure also presented mixed and bonds and out-of-plane buckling. Moreover, it remained stable in our ab initio molecular dynamics simulations carried out at T = 300 K. The calculated electronic properties revealed that monolayers might present conductor or semiconductor behavior, with band gaps ranging from 0.0 to 0.74 eV, depending on atomic arrangement. Tunable values of band gap can be useful in applications. In optoelectronics, for instance, this property might be employed to control absorbed light wavelengths. Our calculations add a new class of monolayers to the increasing library of 2D materials