In Situ Observation of the Effect of Nitrogen on Carbon Nanotube Synthesis

The article examines the in situ observation of the effect of nitrogen on carbon nanotube synthesis. Environmental TEM (ETEM) is a relatively new technique ideal for in situ measurements. Researchers apply ETEM to study the effect of nitrogen on CNT growth, elucidating the mechanisms by which nitrogen acts, to guide efforts to optimize synthesis. To the best of our knowledge, this is the first in situ TEM study of the effect of nitrogen on CNT growth. Therefore, in the absence of ammonia, carbon should precipitate first, resulting in an interface with pure iron. Pure iron has a higher surface tension with the nanotube, which explains the separation of the CNT and catalyst immediately following carbon precipitation. A carbide particle will have a lower surface tension with the nanotube due to its higher carbon chemical potential and thus maintain its contact. The pure iron catalyst may become carbide following cap separation, but this will not affect CNT nucleation.