Sintese e caracterização de nanotubos e fulerenos nitrogenados gerados por arco aletrico

AUTOR(ES)

Roosevelt Droppa Junior

DATA DE PUBLICAÇÃO

2004

RESUMO

This thesis work aims to synthesize and to characterize structural and chemically nanotubes and fullerenes containing nitrogen. Both nanotubes and fullerenes syntheses were performed using an arc-discharge system filled with gaseous mixtures of He e N2. Electron microscopy samples analysis shows that N2 concentration inside the arc-discharge chamber influences the nitrogen incorporation into the carbon structures that give rise to the nanotubes. Those ones containing N atoms in their composition have a bamboo-like aspect in contrast to those generated in absence of nitrogen gas. XPS analyses indicate that nanotube samples generated in N rich atmospheres in fact have nitrogen in their composition and part of N atoms are substitutionally bonded in graphitic sites. EELS data show that N atoms are preferentially bonded in the bamboo-like nanotubes and computational simulations show the role these N atoms play in the formation of these structures. Nitrogenated nanotube samples were also analyzed by Raman spectroscopy. As the samples were irradiated by the Raman laser at different powers, Raman spectra were collected. Such spectra gave information about the structural order and relative purity of the samples. This information coherently complements the electron microscopy data. It was also performed field emission measurements of the nitrogenated nanotube samples. It was verified that such structures are as good emitters as single wall nanotubes (non-nitrogenated ones). It was also observed that nitrogen influences the behavior of the nanotubes structure factor, however, it was not clear yet why this is so. Finally, it was obtained mass spectrometry data of the fullerenes samples. These data indicate the presence of nitrogenated fullerenes or "nitrofullerenes" in the samples generated in nitrogen rich atmosphere. Their molecular masses are around 523 a.m.u.. Theoretical calculations [ 30] also indicate that the existence of such molecules (whose molecular mass is 522 a.m.u.) is possible, since their heat of formation is comparable to that of the C 60fullerenes. XPS data also confirm that there is nitrogen in these samples. The coherence of the experimental as well as the theoretical results strongly suggests that our quest for the heterofullerenes is in the right direction

ASSUNTO(S)

eletrons - emissão nitrogenio carbon nanotubes electron emission nanotubos de carbono fulerenos fullerenes nitrogen

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