Direct synthesis of ultralong carbon nanotube bundles by spray pyrolysis and investigation of growth mechanism.

A mass of ultralong aligned carbon nanotube (CNT) bundles up to about 8 mm in length was synthesized by utilizing the spray pyrolysis of ferrocene/xylene solutions in the absence of promoters, such as thiophene or pure sulfur, and etching agents, such as plasma, oxygen, ethanol or water. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) results indicated the continuous and multi-walled nanotube structure for the CNTs in the macroscopical bundles. A graph demonstrating the correlation between growth time and length of CNT arrays revealed that the maximum growth rate reaches approximately 4612 nm s(-1). Based on the experimental phenomena and results, a continuous rapid growth mechanism in both directions was proposed, which suggests that longer CNT arrays can be synthesized at this rapid growth rate if the growth time is extended.