Growth of carbon nanotubes by chemical vapor deposition

The growth behavior of carbon nanotubes (CNT) deposited from C2H2 by thermal CVD method was investigated. Nickel particles of diameter ranging from 15 to 90 nm were used as the catalyst. CNTs were deposited in various environments of N-2, H-2, Ar, NH3 and their mixtures to investigate the effect of the environment on the CNT growth behavior. The deposition was performed at 850 degreesC in atmospheric pressure. In pure N-2 environment, thick carbon layer deposition occurred on the substrate without CNT growth. The Ni particles encapsulated by the carbon deposition could not work as the catalyst in this condition. However, the growth of CNT was enhanced as the H-2 concentration increased in the mixture of N-2 and H-2 environment. In pure H-2 environment, randomly tangled CNTs could be obtained. The growth of CNT was much enhanced when using NH3 as the environment gas. Vertically aligned CNTs could be deposited in NH3 environment, whereas the CNT growth could not be obtained in the mixture of N-2 and H-2 environment of the same ratio of N/H. These results were discussed in terms of the passivation of the catalyst caused by the excessive deposition of carbon on the catalyst surface. For the deposition of the CNT, the decomposition rate of C2H2 should be controlled to supply carbon for nanotube growth without passivation of the catalyst surface by excessive carbon deposition. The present work showed that the composition of environment gas significantly affects the reaction kinetics in the CNT growth. It is also noted that nitride surface layer formation on Ni catalyst in NH3 environment can affect the CNT growth behavior. (C) 2001 Elsevier Science B.V. All rights reserved.