Influences of NH3 pre-treatment and radicals on the growth of carbon nanotubes

A triple-layered catalyst (Al/Fe/Mo) undergoes considerable restructuring of surface morphology during NH3 annealing prior to carbon nanotube (CNT) growth. The diameter (or density) of AlxOy–Fe clusters formed during the annealing is found to be dependent on the concentration ratio of NH3 to H2O present inside the chamber, which is confirmed by in-situ mass spectroscopy. The different diameter clusters then affect the types of CNTs (i.e. single or multi-walled CNTs) during the growth. Here, a growth model is also presented, where hydrocarbon radicals (C5H9, C6H9, and C6H13) generated from C2H2 pyrolysis (~ 800 °C) can be used as effective precursors to synthesize CNTs.