Carbon Nanotube Nucleation Driven by Catalyst Morphology Dynamics
E Pigos and ES Penev and MA Ribas and R Sharma and BI Yakobson and AR Harutyunyan, ACS NANO, 5, 10096-10101 (2011).
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 sp(2)-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 sp(2)-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.
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