Espectroscopia raman em materiais bidimensionais

• Ano de defesa: 2017
• Autor(a) principal: Ribeiro, Henrique Bücker
• Orientador(a): Souza, Eunézio Antonio de
• Banca de defesa: Rocha, Leandro Seixas , Ardila, Dario Andres Bahamon , Souza Filho, Antonio Gomes de , Moreira, Roberto Luiz
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Presbiteriana Mackenzie
• Programa de Pós-Graduação: Engenharia Elétrica
• Departamento: Faculdade de Computação e Informática (FCI)
• País: Brasil
• Palavras-chave em Português: espectroscopia raman; materiais bidimensionais; materiais lamelares
• Área do conhecimento CNPq: CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA::FISICA DA MATERIA CONDENSADA; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA::FISICA DA MATERIA CONDENSADA::PROP.OTICAS E ESPECTROSC.DA MAT.CONDENSOUTRAS INTER.DA MAT.COM RAD.E PART.; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA::FISICA DA MATERIA CONDENSADA::RESSONANCIA MAG.E RELAX.NA MAT.CONDENSEFEITOS MOSBAUERCORR.ANG.PERTUBADA
• Link de acesso: http://dspace.mackenzie.br/handle/10899/24285

In this thesis, the properties of four kinds of layered materials were investigated: twisted bilayer graphene, black phosphorus, germanium selenide (GeSe) and germanium sulfide (GeS) (group IV monochalcogenides) by means of Raman spectroscopy. The Raman spectrum of different twisted bilayer graphene samples rotated by different angles ranging from 0 to 30 was measured using three lasers with wavelengths of 488 nm, 532 nm, and 633 nm. The electronic structure of the investigated samples was mapped and the energy in which the resonances take place were attributed to the presence of van Hove singularities that are related to the size of Moiré cell. Angular dependence measurements of the Raman spectrum on black phosphorus (BP) samples were also performed and it was demonstrated that the angular dependence of the Raman band intensities presents an unusual behavior. In order to explain such behavior, one must consider the complex nature of the Raman tensors. Furthermore, the atomic structure and phonon behavior in the vicinity of the BP sample edges were also studied using polarized Raman spectroscopy and the experimental results were explained by using density functional theory calculations. Polarized Raman spectra showed the appearance of some modes at the edges of the samples prohibited by symmetry selection rules. Theoretical simulations confirm that this symmetry breaking originates from an atomic rearrangement at the edges of the crystal. A similar behavior was also observed for GeS and GeSe samples and the appearance of Raman modes of the edges was attributed to the reorganization of the atoms of the crystal edges, since their crystal structure are similar to that of BP crystals.