Evolution of Nanocatalyst Structure and Composition during Chemical Vapor Deposition Synthesis of Single-Walled Carbon Nanotubes

Abstract

Various aspects of the catalytic synthesis of single-walled carbon nanotubes (SWCNTs) on transition metal nanoparticles were studied by combining atomistic simulations: reactive molecular dynamics (RMD), density functional theory (DFT), and ab initio molecular dynamics (AIMD), with in situ high-resolution environmental transmission electron microscope (ETEM) imaging. SWCNTs are carbon allotropes with applications in many technological fields owing to their exceptional properties that depend on their structural features. Understanding the nucleation and growth of SWCNTs can provide the tools to devise strategies to control their structure from the synthesis, thus allowing further development and implementation of nanotube-based technologies.

The interactions of supported and unsupported carbon-philic and noble transition metal catalytic nanoparticles with adsorbed or dissolved carbon and nanotube seeds were investigated using DFT and AIMD simulations. These studies revealed differences in solubility and nucleation mechanisms on the different particles due to interactions with added C and the support. A cooperative nucleation mechanism was demonstrated using ETEM measurements and DFT, in which different facets of the catalyst with stronger/weaker adhesion facilitate nucleation/lift-off of the seed to form the nanotube. ETEM and RMD of supported Co catalyst during nanotube growth revealed structural changes in the nanoparticle and the coexistence of metal and carbide regions of fluctuating size directly affecting the growth rate and catalyst structure.