Figure 1

(a) The SWNT-metal catalyst particle interface, where the circular tube open end is attached to a circular metal step edge on the catalyst particle. (b) A fraction of the SWNT-catalyst step interface is modeled by an interface of graphene-stepped metal surface [represented by the Ni(111) surface here]. A repeatable cycle of incorporating two C atoms into a new 6-membered-ring (6MR) on a CNT AC site involves 4 serial steps: (i) the decomposition of C feedstock molecules on catalyst surface; (ii) decomposed C atoms diffuse to a AC site; (iii)-1 and (iii)-2 the direct incorporation of the first and second C atoms into the AC site to form a new 6MR [the details of (iii)-1 and (iii)-2 shown in (c) and (d)]; (iv) the etched metal atom diffuse away, leading to a reconstruction of the catalyst.Reuse & Permissions

Figure 2

Energy profile for incorporating two C atoms into graphene on Ni(111) surface serially. A full cycle has zero energy change and the overall barrier $G_0^{*}$ equals the barrier of a reverse procedure $G_R^{*}$ when C in graphene is treated as initial feedstock. Using active C feedstock reduces the barrier to $G_0^{*}-2\Delta \mu$, where $\Delta \mu$ is the chemical potential difference between a C in graphene and in feedstock. The details of feedstock decomposition, C diffusion, and metal diffusion are ignored and shown by dashed lines. In the figure, “decom.&diff.” stands for decomposition and diffusion and “diff.&catal. rec.” stands for diffusion and catalyst reconstruction.Reuse & Permissions

Figure 3

CNT growth rate on Ni, Co, Fe surfaces versus growth temperature at different $\Delta \mu$ (in eV).Reuse & Permissions