The importance of supersaturated carbon concentration and its distribution in catalytic particles for single-walled carbon nanotube nucleation

The carbon concentration in catalytic metal particles during the initial stages of single-walled carbon nanotube (SWNT) nucleation is studied by thermodynamics modelling and molecular dynamics simulation. Highly supersaturated carbon concentrations are necessary for nucleating the initial small carbon structures (e.g., islands) on the particle surface. A lower, but still supersaturated, concentration is required to enlarge the carbon island, with the required carbon concentration decreasing with increasing island size. This decrease in carbon concentration explains the widely observed phenomenon that only one carbon nanotube is nucleated per catalyst particle in catalytic chemical vapour deposition experiments. It is also shown that an inhomogeneous distribution of carbon in the catalyst particle can lead to the formation of several SWNTs from each particle, as formed in arc discharge and laser ablation experiments.