Propriedades eletrônicas, estruturais e vibracionais de nanoestruturas de carbono 1D e 2D sob altas pressões

Abstract

The main scope of this thesis is the study of nanostructured carbon hybrid systems. Hybrid means the confinement of atoms and molecules in carbon nanotubes and bilayer graphene. In the first work, bundles of carbon nanotubes were investigated, whose nanotubes are filled with linear carbon chains (carbynes). We carried out an investigation under extreme pressure conditions that aimed to study them in terms of their mechanical resistance and their physical-chemical transformations. The density functional theory together with molecular dynamics were the tools used to develop this study, which revealed the stability of new sp3 bonds promoted between carbynes and the inner surface of nanotubes, as well as between the external surfaces of adjacent nanotubes, bonds promoted in the flat region of nanotubes and which differ from the more conventional bonds in the curved region of collapsed nanotubes. In a second work, also using the density functional theory together with molecular dynamics, we investigated the vibrational properties of carbynes confined inside carbon nanotubes, the results allowed advance in the understanding of experimental results of Raman spectroscopy such as the occurrence of the redshift on the frequencies of the confined chains after the collapse of nanotubes influenced by high pressures. The molecular dynamics results played an important role in shedding light on the mechanisms originating from the pressure-induced chain coalescence process. Still, in systems consisting of nanotubes, we investigated the spectral behavior of the resonance of quaterthiophene molecules inserted inside nanotubes as a function of pressure. Density functional theory was the chosen tool for this investigation, where it was possible to understand the piezo-resonance behavior in the Raman spectrum of quaterthiophene associated with the pressure-induced cross-sectional collapse of carbon nanotubes. In the last work, we used the density functional theory to investigate hybrid systems based on bilayer graphene intercalated with Li and K alkali metals. This investigation aimed to understand the possibility of the emergence of new covalent bonds, induced by uniaxial strain or hydrostatic pressure, between the layers themselves, moreover, we found that these new bonds did not show stability in the absence of strain, however, the presence of a pressure transmitting medium indicates a possible important agent for making the chemical bonds between the layers stable. In addition, the results suggest that these structures could be candidates for superconducting materials.