Two-stage growth of single-walled carbon nanotubes
The growth of single-walled carbon nanotubes (SWNTs) in a chemical vapor deposition (CVD) system is a complex process. In a typical growth mechanism, the process includes the nucleation stage, the growth stage, and the termination stage. However, most nanotube growth experiments were performed under identical growth conditions for different stages. Here, a two-stage growth process is studied with different growth environments at the nucleation stage and growth stage. Priming the catalysts with carbonaceous species is treated as a wholly separate process from nanotube growth throughout this work. The optimum conditions for these two stages are found to be different. Conditions that give a high yield of active catalysts will cause impurities to cover the catalysts and halt growth. Similarly, conditions that allow prolonged growth of nanotubes will fail to activate all of the catalysts, resulting in low overall yield. The yield of carbon nanotube growth by CVD can be significantly improved by using a higher carbon feeding rate in the nucleation stage followed by lower carbon feeding rate for continued growth. © 2007 American Chemical Society.
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