Mechanism of the initial stages of nitrogen-doped single-walled carbon nanotubegrowth

Abstract

We have studied the mechanism of the initial stages of nitrogen-doped single-walled carbon nanotube growth illustrated for the case of a floating catalyst chemical vapor deposition system, which uses carbon monoxide (CO) and ammonia (NH₃) as precursors and iron as a catalyst. We performed first-principles electronic-structure calculations, fully incorporating the effects of spin polarization and magnetic moments, to investigate the bonding and chemistry of CO, NH₃, and their fragments on a model Fe₅₅ icosahedral cluster. A possible dissociation path for NH₃ to atomic nitrogen and hydrogen was identified, with a reaction barrier consistent with an experimentally determined value we measured by tandem infrared and mass spectrometry. Both C–C and C–N bond formation reactions were found to be barrierless and exothermic, while a parasitic reaction of HCN formation had a barrier of over 1 eV.