Nucleation and growth of carbon nanotubes and nanofibers: Mechanism and catalytic geometry control

Abstract

Carbon nanotubes and nanofibers with certain shape, size and structure are desired. The study of the kinetics of nucleation and growth of carbon nanotubes and nanofibers is an important key to understand and control the growth process. That knowledge will greatly improve our capacity to optimize structural shapes and increase growth rates. This Perspectives article draws from the literature on carbon nanotube growth and analyzes them to reveal some aspects underlying reaction mechanisms. In each catalyst nanoparticle a constant carbon bulk diffusion flux operates between two distinct catalytic areas with different roles: 1) Surface catalysis producing carbon atoms in some areas; 2) Graphene nucleation and growth, in other areas. Preliminar solid-state changes – obeying 2nd Fick’s law – may take place. Subsequent kinetic linearity is the sign that a steady-state 1st Fick’s law controlled growth process has been established. Data from the literature on diverse crystal orientations activity are discussed. Catalyst duality may be based on different crystal faces or on solid-state phases prevailing during steady-state growth. Growth of carbon nanotubes from Ni nanoparticles usually described as “octopus” carbon offers evidence of the role of geometry, pentagon formation “catalysis” and catalyst duality operating at low temperatures.