(706h) Diffusion Mechanisms of Carbon During Single-Walled Carbon Nanotube Growth On Supported Metal Nanoparticles: The Effect of Temperature

A highly controlled synthesis of single-walled carbon nanotubes requires a clear understanding of the mechanisms involved. However, understanding the role and mechanism of carbon diffusion and dissolution during chemical vapor deposition synthesis still remains a challenge. Our contribution addresses this issue by examining the individual trajectories of carbon atoms in reactive molecular dynamics simulated growth of single-walled carbon nanotubes on supported Ni nanoparticles. We identify carbon atoms participating in surface diffusion, bulk diffusion, and potential carbide formation by observing the dynamic evolution of the system at fixed nanoparticle size and adhesion energy of the nanoparticle to the substrate, at different temperatures, 750, 900 and 1000 K. Nanoparticle saturation with carbon and changes in the catalytic regime determine the transitions between induction, nucleation, and growth stages. From our results at 1000K, we found that due to the low-energy barrier for surface diffusion, nucleation may occur simultaneously with dissolution before saturation is reached. Induction and nucleation are governed preeminently by bulk diffusion, while growth is by surface diffusion. Additionally, Ni/C ratios were found to be compatible with stoichiometries of known Ni carbides. Here we examine the effect of lowering the synthesis temperature that may have a significant impact in the nanoparticle morphology and consequently on the carbon solubility inside the nanoparticle.