Maximization of carbon nanotube yield by solid carbon-assisted dewetting of iron catalyst films

Further understanding of how nanoparticle catalyst composition influences the yield of carbon nanotubes (CNTs) is key to their scalable, cost-effective manufacture. In particular, the role of trace carbon deposits on promoting CNT nucleation from the catalyst has been studied recently by our team. Here, we show that deposition of solid carbon onto an iron catalyst film prior to dewetting effectively amplifies the CNT yield. We investigated the effect of the amount of C and Fe on particle formation and reduction, and growth kinetics using a combination of in situ techniques – Raman spectroscopy, X-ray photoelectron spectroscopy and environmental transmission electron microscopy. We found that CNT growth rate and yield are maximized for specific relative thicknesses of C and Fe (∼0.2 and 0.8 nm, respectively). The presence of carbon causes accelerated dewetting of the catalyst, and more rapidly forms a population of metallic Fe particles that grow CNTs at a higher yield. These factors also cumulatively result in a lower incubation time and improved yield. Therefore, loading of catalyst particles with solid carbon is a straightforward and practical route towards boosting CNT yield and improving the efficiency of CNT growth by chemical vapor deposition.