Growth mechanism of carbon nanotube forests by chemical vapor deposition

Abstract

Analysis of kinetics processes involved in carbon nanotube (NT) forest growth during chemical vapor deposition suggests that: (i) carbon species are unable to penetrate to the forest bottom whenever the mean free path in gas is much larger than the typical distance between NTs; instead they collide with NT surfaces, chemisorbing within the top few microns, diffuse along the surface, and feed the growth at nanotube tips, (ii) wherever a catalyst nanoparticle is present, at the substrate or on the nanotube tip, in the postnucleation stage its role in feeding NT growth by C dissolution and bulk diffusion is negligibly small in comparison with the surface diffusion of C species adsorbing on the lateral surface of nanotubes, and (iii) bulk diffusion of C through the catalyst nanoparticle, defining the characteristic times of C penetration to nanoparticle base and surface saturation with C, is shown to play a major role in selection of the initial mode of nanotube nucleation and growth.