Optical emission spectroscopy study of the influence of nitrogen on carbon nanotube growth

In-situ optical emission spectroscopy was used to systematically study the influence of nitrogen on the growth of carbon nanotubes (CNTs) by microwave-plasma enhanced chemical vapor deposition at different CH, concentrations in a CH4/N-2 gas mixture. The results show that CN and C-2 co-exist in the plasma and emission intensities of the two species. are correlated. The morphology and microstructure of the samples vary with the CH4 concentration. Well aligned nanotubes are obtained at 20% CH4. With the participation of N-2, the CNTs present a polymerized nanobell structure. More importantly, the length and thickness of each nanobell can be modulated by varying the CH4 concentration. Without N-2, conventional cylindrical CNTs are obtained. (C) 2003 Elsevier Science Ltd. All rights reserved.