Carbon Nanotube Nucleation From Graphitic Nanofragments3

A detailed analysis of nanotube nucleation from graphitic nanofragments by thermal vibration via the interaction with amorphous carbon, fullerene-like and carbonized metal catalyst nanoparticles is given predicting a variety of nanotube chiralities observed experimentally. The issue of kinetic selection between (i) carbon nanosheet wrapping around the metal nanoparticle, (ii) NT growth from the nanoparticle surface by the root mechanism and (iii) metal nanoparticle surface being covered by an amorphous carbon layer is considered. The temperature fall rate and the heat dissipation by the inert gas are shown to play a crucial role in providing conditions for the root mechanism of NT nucleation. At low inert gas pressure the heat dissipation is very slow and the time required for particle cooling and C segregation is comparable with the characteristic time of C impingement into the surface from vapor. Under these conditions nanoparticles will be covered by C impinging from the vapor, and the root mechanism of NT nucleation is inhibited. In this case the nanoparticle provides a template for carbon condensation which can lead to the formation of a graphitic layer and nanoring nuclei wrapped around the nanoparticle. However, at inert gas pressures >0.1 bar the characteristic time for metal-carbon nanoparticle cooling becomes much lower than the characteristic impingement time of C from vapor providing conditions for NT nuclei formation by the kinetic pathway of C segregation from metal particle and root mechanism.