The effect of catalysis on the formation of one-dimensional carbon structured materials

Carbon nanotubes (CNTs) have been synthesized by catalytic chemical vapor deposition (CCVD). Catalysts, e.g. Fe, Ni, Co, etc., are very important in the formation of CNTs. Other elements, such as Cu, although showing no effect on growth, have been used to enhance the catalytic effect of Ni by alloying it with Ni. In this study, one-dimensional carbon structured materials were synthesized by microwave plasma enhanced chemical vapor deposition (MPECVD) with a mixture of methane and hydrogen as precursors at a temperature of similar to600degreesC. Subsequently, the samples were taken into thermal treatment (under a mixing atmosphere of Ar and H-2, up to 1000degreesC) in order to improve the graphitization of CNTs. The result shows that the increase of Cu from 40 to 60 at.% in Ni/Cu alloys changes the morphology of carbon from tubules to filaments, and meanwhile the tangled conditions were lessened in this Ni-Cu alloy range. Aligned carbon nanotubes were effectively catalyzed at Cu <40 at.%, and interestingly enough the existence of carbon nanoclusters at Cu>60 at.% was observed. Images from high-resolution transmission electron microscopy (HRTEM) showed that the CNTs were multiwalled and graphitized structures were confirmed by Raman spectra. (C) 2002 Elsevier Science B.V. All rights reserved.