Polyyne Ring Nucleus Growth Model for Single-Layer Carbon Nanotubes

We propose, based on recent experimental results, a polyyne ring nucleus (PRN) growth model for the synthesis of single-layer nanotubes (SLN's). The PRN model assumes that (i) the critical nuclei are the planar carbon polyyne rings that are observed to be most stable for sizes in the range ${\mathrm{C}}_{10}$ to ${\mathrm{C}}_{40}$; (ii) C${\mathrm{o}}_{\mathit{m}}$ ${\mathrm{C}}_{\mathit{n}}$ clusters (possibly charged) play the role of a catalyst by serving to add ${\mathrm{C}}_2$ or other gas phase species into the growing tube; (iii) promoters such as S, Bi, and Pb serve to modify the rates for these processes by stabilizing the ring structure. We suggest experiments to test and amplify this PRN model, including a flow tube arrangement that might be useful for synthesizing more uniform SLN's.