Effect of catalyst composition on carbon nanotube growth

Transmission electron microscopy was used to probe the compositions of individual Co–Mo bimetal catalyst particles and the morphologies of carbon nanotubes (CNTs) catalyzed by these particles under flowing carbon monoxide at $\text{700\hspace{0.05em}°}\mathrm{C}.$ It was found that the composition of the catalyst particle at a CNT tip and the distribution of Co within the particle largely determine the morphology of the CNT. A particle with low Co content $\text{(<15\hspace{0.17em}}\mathrm{at.}\mathrm{ \%)}$ tends to produce a long CNT, while a particle with very high Co content $\text{(>85\hspace{0.17em}}\mathrm{at.}\mathrm{ \%)}$ tends to produce onion-like structures. These observations provide insight into the CNT growth mechanisms.