A molecular level model for the nucleation of a single-wall carbon nanotube cap over a transition metal catalytic particle

Recent in-situ video rate TEM studies have revealed that the base growth of single-wall carbon nanotubes (SWCNT) in thermal chemical vapour deposition (CVD) is accompanied by a considerable deformation of the Ni catalyst nanoparticle and the creation of a subsurface carbon layer. In this paper we argue that these effects may be produced by the adsorption – on the catalyst nanoparticle – of cyclopentadienyl ions formed in gas phase during C2H2 pyrolysis. These ions can, at the same time, facilitate the nucleation of a SWCNT cap by the provision of “ready made” pentagons. To this end we have performed semi-empirical quantum mechanical calculations with the ZINDO method. The results support the above proposed mechanism. We also suggest that this mechanism could also explain the increased rate of SWCNT production in plasma enhanced CVD, where these ions are expected to be present in higher concentrations during C2H2 pyrolysis.