Endofullerenes with Metal Atoms Inside as Precursors of Nuclei of Single-Walled Carbon Nanotubes
Thermodynamic estimations have been made which show that amorphous carbon cannot be the source of single-walled carbon nanotube growth during carbon/metal vapor condensation. Thus the source of carbon material for nanotube growth seems to be small carbon clusters into gas phase or clusters in the adsorbed state on the nanotube surface. Kinetic analysis of carbon/metal vapor condensation in the arc process was performed and showed that metal vapor becomes supersaturated at temperatures that are close to the temperature of the highest rate of fullerene shell formation. A new model of the nucleation of single-walled carbon nanotubes is proposed. In the model an endometallofullerene serves as the precursor of a nanotube nucleus, and the nucleus itself forms as an adduct arising after metal atoms attach to the endofullerene shell. The relative efficiencies of La/Ni, Gd/Ni, Ce/Ni, and Pr/Ni catalysts, in comparison with Y/Ni catalyst, were measured, and their high efficiency in buckytube formation was demonstrated. This fact was explained by the double action of a metal catalyst in buckytube nucleus formation. First, metal takes part in the formation of endometallofullerenes. Second, the metal atoms attach to the endofullerene shell to transform an endofullerene into a nanotube nucleus. The high performance of bimetallic catalysts lies in adjusting the values of two metal concentrations separately for each of these purposes. In accordance with observations, the proposed model predicts increasing size of endofullerenes with increasing concentration of the metal that controls endofullerene formation.
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Document Type: Research Article
Publication date: 2004-04-01
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