Carbon Nanotube Nucleation Driven by Catalyst Morphology Dynamics
ACS Nano, 5 (12), pp 10096–10101
In situ observation of the carbon nanotube nucleation process accompanied by dynamic reconstruction of the catalyst particle morphology is considered within a thermodynamic approach. It reveals the driving force for the detachment of the sp2-carbon cap, so-called lift-off—a crucial event in nanotube growth. A continuum model and detailed atomistic calculations identify the critical factors in the lift-off process: (i) catalyst surface energy, affected by the chemisorbed carbon atoms at the exterior surface of the catalyst, exposed to the carbon feedstock; and (ii) the emergence of a pristine, high-energy facet under the sp2-carbon dome. This further allows one to evaluate the range of carbon feedstock chemical potential, where the lift-off process occurs, to be followed by emergence of single-walled nanotube, and provides insights into observed catalyst morphology oscillations leading to formation of multiwalled carbon nanotubes.