Efeito de strain perpendicular em bicamadas híbridas

• Ano de defesa: 2017
• Autor(a) principal: Silva, Thiago de Souza
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal da Paraíba; Brasil; Física; Programa de Pós-Graduação em Física; UFPB
• Palavras-chave em Português: Bicamadas; Híbridos; Strain; Adsorção de Hidrogênio,; Estrutura Eletrônica,; DFT; Bilayer; Hybrids; Hydrogen Adsortion,; Electronic Structure; CIENCIAS EXATAS E DA TERRA::FISICA
• Link de acesso: https://repositorio.ufpb.br/jspui/handle/tede/9828

In the present work, we use first-principles calculations based Density Functional Theory, as implemented in the SIESTA and SIESTA-TRUNK, which takes into account the Van der waals interactions, codes, to investigate the stability and electronic properties of graphene monolayers with a nanodomain of hexagonal boron nitride (h-BN) with different shapes and sizes. These heterostructures can be obtained through graphene growing in atomic layers of h-BN lithographically patterned and sequential chemical vapour deposition, so that its possible to construct nanodomains of h-BN with an shape or size in graphene. First we will study the effects, in stability, magnetic and electronic properties, of the adsorption of one and two atoms of hydrogen in the edges of the h-BN nanodomain. The alterations that occur in graphene heterostructures with circular h-BN nanodomains, with the same number of boron and nitrogen atoms, and with triangular form with boron terminated edges, where there are more boron atoms than nitrogen atoms, and with nitrogen terminated edges, where there are more nitrogen atoms than boron atoms, this way we can study the effects of hydrogen adsorption in systems with the same number of electrons and holes, with holes in excess and with electrons in excess, respectively. We observe that the electronic and magnetic properties are influenced by the type of atom on which the the hydrogen atom is adsorbed. Besides that, we show that the heterostructures with triangular shaped nanodomains are more stable. Then we study the stability, electronic properties and the effects of perpendicular strain in hybrid bilayers using the GGA and VDW-DF approximations for the exchange-correlation functional. Initially we study bilayer composed of graphene monolayers with a B3N3 nanodomain in hexagonal shape and stacked in various different configurations. We realized that the Bernal stacking configuration (graphite-like) is more stable when compared to the others. Besides that, we could see that the ideal interlayer distance is smaller when we do the calculations with the VDW-DF approximation than when we use the GGA approximation. We study the effect of perpendicular strain, represented by the variation of the interplanar distance, only in the structure which showed to be more stable and, we verify that, the strain is capable of opening the energy gap in the system. In our analyses we also noticed that the band structures of the systems are the same independent of the approximation. Lastly we make a study on the stability, electronic properties and the effects of strain in hybrid bilayers with different geometries. We use the VDW-DF approximation for the exchangeABSTRACT vii correlation functional. The geometries of the h-BN nanodomains, present in each monolayers, are B12N12 in circular shape, B10N6 and B6N10 in triangular shape, we study various combinations of these monolayers in a bilayer system. We found that the Bernal form of stacking has shown to be more stable in all studied configurations and the the interaction between monolayers tends to decrease the energy gap of the system. We analyse the effect of strain onl y in the configuration that has shown to be more stable e we verify that the perpendicular strain is capable of opening the energy gap of the bilayer.