(290a) Impact of Support, Nanoparticle Size, and Carbon Precursor on the Nanotube Growth Mechanism: Viability of Controlling Nanotube Structure

Single-walled carbon nanotubes are tubular crystalline materials that can be grown via chemical vapor deposition (CVD) and have outstanding electronic and optical properties that are potentially useful for a myriad of applications.  However, such properties can vary significantly with the individual nanotube structure, which can be defined by the chirality (n,m).  Therefore, designing a highly chiral-selective and large-scale nanotube synthesis process has been highly sought-after to avoid costly post-synthesis separation processes.  Such level of control, however, demands a clear understanding of the nanotube growth mechanism, which is still under debate due to seemingly conflicting experimental observations.  In this contribution, we use reactive molecular dynamics to simulate nanotube growth at 1000 K under different conditions with variations of i) nanocatalyst particle size, ii) carbon feedstock, and iii) interaction strength between the nanocatalyst and the support.  We used computational tools to analyze the carbon diffusion mechanism and nanotube assembly, and the structural and dynamic state of the nanoparticle (and the possibility of carbide formation), and discuss our findings in the context of the viability of using the nanocatalyst particles as a template to control nanotube chirality.  For instance, dissolution of carbon during the induction/nucleation period increases the dynamics of the nanocatalyst particle (surface), which is unfavorable to create a template effecting on the emerging carbon network.  However, we observed that carbon dissolution and the formation of the carbon network happen as parallel processes, indicating that the latter can occur with or without the former.  This finding reconciles the observation of nanotube growth in both carbon-dissolving and non-carbon-dissolving materials, and suggests that the latter scenario can be potentially exploited to achieve templated nanotube growth.