Flame synthesis of Fe catalyzed single-walled carbon nanotubes and Ni catalyzed nanofibers: growth mechanisms and consequences

Flame synthesis of single-walled carbon nanotubes and nanofibers is demonstrated using a pyrolysis flame configuration. Fe reacts preferentially with CO/H2/He mixtures to produce single-walled nanotubes (SWNTs). In contrast, Ni reacts preferentially with C2H2/H2/He mixtures to yield nanofibers. Both catalyst metals exhibit a marked size dependent reactivity towards these reactant gas mixtures. The yarmulke mechanism and a carbon solvation/diffusion/precipitation account for the different catalyzed products; SWNTs and nanofibers, respectively. Consequences of the size dependent reactivities of Fe and Ni nanoparticles and the respective growth mechanisms for the SWNTs and nanofibers are discussed.