Estudo das propriedades de transporte elétrico de grafeno hidrogenado

• Ano de defesa: 2009
• Autor(a) principal: Daniel Cunha Elias
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Transporte elétrico; Grafeno hidrogenado; Transporte eletrico; Física; Grafeno
• Link de acesso: http://hdl.handle.net/1843/ESCZ-7ZEG7B

Graphene is a strictly two-dimensional material with carbon atoms arranged in honeycomb lattice with strong sp2 bonds. It has as a peculiar linear dispersion around the K and K points of the Brillouin zone. Graphene samples are obtained by micromechanical cleavage and can be located on the top of a properly chosen substrate by using an optical microscope. The measured resistivity as a function of gate voltage of a graphene Hall device shows a maximum value of ~h/4 at the neutrality point which is temperature independent. Electrical transport in a graphene device is due either to electron or holes which are selected by the sign of the applied gate voltage. This material presents an anomalous quantum Hall effect which is attributed to the chirality of the charge carriers in this system. In this work, we have measured the resistivity versus gate voltage of graphene devices at different temperatures and show that electrical transport in this material is strongly affected by extrinsic scatters. Intrinsic scatters can limit the carrier mobilities to values as high as ~200 000 cm2V-1s-1, at room temperature. Analysis of the resistivity of graphene samples at different temperatures show that this scattering is due to flexural phonons confined in ripples which are formed in graphene. We have also demonstrated a process of reversible hydrogenation of graphene. Hydrogenation of graphene is carried out by submitting samples of this material to a hydrogen plasma. In this process, the hybridization of carbon atoms changes from sp2 into sp3 leading to observable changes in its structure and in its electrical conduction. These findings have been confirmed by electrical transport measurements, Raman studies and by transmission electron studies. We show that hydrogenation of graphene is not uniform and is more effective in free-standing membranes than for graphene on a substrate. The hydrogenation is a reversible process and the sample properties can be restored by annealing. We show that it is possible to use graphene to store hydrogen and also show evidence of a graphane material.