Do We Really Know Why Carbon Nanotubes Grow?

The mesoscopic-level formation mechanism of carbon nanotube growth, particularly the transition from a graphene patch to a tube, remains unclear. Recent studies have focused on finding a complete description of this phenomenon to understand its origin and to have total control over the formation of carbon nanotubes. In this study, a thermodynamic model is proposed that follows the sharp interface model approach, in which all energy contributions to the total energy of the nanotube are identified as bulk or surface terms. This study proposes an additive model to calculate the total energy of these structures and identify the dominant energy contributions that determine whether the adsorbed carbon atoms form a growing cap on the catalyst nanoparticle or initiate a new carbon nanotube perpendicular to the surface. By comparing the total energy of these two mechanisms, the research aims to elucidate the energetic driving force behind each pathway for optimizing future nanotube growth processes. We also discuss the generality of the model introduced in this article, showing how it can incorporate temperature and disorder effects, thereby enabling the description of both vapor-solid-solid and vapor-liquid-solid mechanisms of carbon nanotube formation at relevant operating conditions. Finally, we outline a strategy for a genuine multiscale framework that combines the microscopic, atomistic picture of carbon nanotube formation with a meso/macroscopic nucleation and growth representation based on a sharp-interface model.