Effect of NH₃ Environmental Gas on the Growth of Aligned Carbon Nanotube in Catalystically Pyrolyzing C₂H₂

Minjae Jung, Kwang Yong Eun, Young-Joon Baik, Kwang-Ryeol Lee, Jin-Koog Shin and Sung Tae Kim

It has been well known that vertically aligned carbon nanotubes (CNTs) can be grown by thermal CVD in NH₃ environment. However, the mechanism of the vertically aligned CNT growth is yet to be clari ed. In the present work, we investigated the e ect of NH₃ gas on the CNT growth in the view point of catalyst passivation. The particles of Ni or Co of diameter ranging from 17 to 58 nm were used as the catalyst. CNTs were deposited at 950 ^oC using C₂H₂ in various environments of NH₃ , H₂ , or their mixtures. In H₂ environment, signi cant catalyst passivation was observed at the C₂H₂ concentration of 2.4 vol.% due to the excessive supply of carbon. However, vertically aligned CNTs were deposited in NH₃ environment even when the C₂H₂ concentration was 16.7 vol.%. From the composition analysis of the catalyst surface, we could show that activated nitrogen atoms were generated by the decomposition of NH₃ . Two possible roles of the nitrogen were suggested based on the bamboo growth model. The nitrogen atoms enhance the formation of graphitic layer and/or improve the separation kinetics of the graphitic layer from the catalyst. The growth behaviors without the pretreatment for 1 h in NH₃ environment showed that the role of the nitrogen appeared in di erent way depending on the catalyst materials. In the case of Co catalyst, where vertically aligned CNT growth was observed without the pretreatment, enhanced formation of the graphitic layer might be the signicant role of the nitrogen. However, when using Ni catalyst, the pretreatment in NH₃ environment was required for the CNT growth, which implies that both the formation and the separation of the graphitic layer were essential.