Effects of Precursor Type on the CVD Growth of Single-Walled Carbon Nanotubes
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Single-walled carbon nanotubes (SWCNTs) can be grown using chemical vapor deposition methods consisting of the catalyzed decomposition of a precursor gas on the surface of (usually) metal nanocatalysts. Among the many variables affecting the process, the nature of the precursor gas is particularly interesting because nanotube growth mechanism may be closely dependent on the specific decomposition products. Here we investigate and compare simulated SWCNT growth under two precursor decomposition products: single carbon atoms and dimers. Specifically we evaluate the effect of the precursor type on carbon association within the nanoparticle, nanotube quality, and nanotube chirality. Compared to a synthesis based on carbon atoms as the main dominant species, it is found that when carbon dimers are the main precursor decomposition products, carbon dissolution as well as carbon association inside the nanoparticle are slowed down, and nucleation is accelerated, increasing the risk of carbon encapsulation. In the growth stage, dimers can be incorporated into the nanotube rim without previous splitting. As a consequence, the kinetics of self-healing is altered, favorably affecting the quality of the nascent tube, evaluated through the formation of hexagonal rings and occurrence of bamboo growth. Finally, the dimer precursor product results in a moderate bias toward formation of near-arm-chair chiralities. 2013 American Chemical Society.