ABSTRACT
Carbon nanotubes produced from carbon vapor generated by arc discharge or laser ablation of graphite generally have fewer structural defects than those produced by other known techniques. This is due to the higher growth process temperature that ensures perfect annealing of defects in tubular graphene sheets. Multiwalled nanotubes (MWNTs) produced by these high-temperature methods are perfectly straight, in contrast to kinked tubes produced at low temperatures in metal-catalyzed chemical vapor deposition (CVD) processes. While the quality of low-temperature tubes can be improved by prolonged postsynthesis annealing at temperatures above 2000 K, the mechanical and electrical properties of arcproduced MWNTs remain far superior. Very high-quality nanotubes are vital for many applications that do not require multi-ton tube quantities; therefore, high-temperature production methods will not be completely replaced by more productive catalytic methods. On the contrary, the need of industry for the highest quality nanotubes will likely steadily grow, thus making it necessary to scale up the hightemperature production methods. Single-wall nanotubes (SWNTs) are almost lacking in structural defects independent of the synthesis process; therefore, alternative methods already strongly compete with arc
and laser techniques and may surpass and substitute for them in future bulk production. The extent of this substitution will depend on other important qualities of the SWNT product, such as uniformity of tube chirality, size distribution, and ease of purification. It remains unclear which production process will eventually better ensure such qualities. Either the arc or the laser method may eventually be preferred. Thus, there are grounds to intensively pursue both further studies and methods of scaling up each process. Knowledge of the nanotube growth mechanism is the basis for success in scaling up efforts and in obtaining desirable nanotube qualities, and therefore it is given much attention in this chapter.
