Growth of Carbon Nanotubes by Chemical Vapor Deposition

Minjae Jung, Kwang Yong Eun, Jae-Kap Lee, Young-Joon Baik, Kwang-Ryeol Lee and Jong-Wan Park 

 The growth behavior of carbon nanotubes (CNT) deposited from C₂H₂ by thermal CVD method was investigated.  Ni particles of diameter ranging from 15 to 90 nm were used as the catalyst.  CNTs were deposited in various environments of N₂, H₂, Ar, NH₃ and their mixtures to investigate the effect of the environment on the CNT growth behavior.  The deposition was performed at 850C in atmospheric pressure.  In pure N₂ 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 H₂ concentration increased in the mixture of N₂ and H₂ environment.  In pure H₂ 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 N₂ and H₂ environment of the same ratio of N/H.  These results were discussed in terms of the passivation of the catalyst caused by the exessive 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.