(37a) Exploring the Best CVD Conditions for Growth of Small-Diameter Single-Wall Carbon Nanotubes Using an Autonomous Research System

Due to the breadth of parameters that affect growth of single-wall carbon nanotubes (SWCNTs) via chemical vapor deposition, rapid experimentation is a powerful tool for investigating conditions for selective growth of small-diameter SWCNTs. Here we utilize an Autonomous Research System (ARES)—an automated, high throughput, laser-induced CVD system with in situ Raman spectral feedback—to study the roles of Ru promotion of Co catalyst and type of feedstock in the growth of small-diameter SWCNTs at different temperatures. We demonstrate through over 200 growth experiments in ARES and ex-situ multi-excitation Raman spectroscopic characterization that Ru-promoted Co catalyst nearly doubles the selectivity of small-diameter SWCNTs (diameters below 1nm) between growth temperatures of 650°C and700°C in comparison to pure Co. At elevated temperatures between 800 and 850°C, Ru stabilizes Co catalyst nanoparticles and increases the selectivity of small-diameter SWCNTs by almost a factor of three. Results reveal SWCNT diameters are not only dependent on the size of the catalyst but also on the precursor chemistry as selectivity towards small-diameter SWCNTs decreases in the following order: ethylene > acetylene (1% in He) > FTS-GP (Fischer-Tropsch synthesis gaseous product mixture). Density functional theory (DFT) simulations using 13- and 55-atom clusters with similar Ru/Co ratios provide mechanistic insight into the observed phenomenon, revealing increased cohesive energies of Co clusters after the addition of Ru irrespective of the location. Our findings indicate the presence of ~10% Ru in Co increases the sintering resistance and stability of small nanoparticles, as well as selectivity towards small-diameter SWCNTs.