Coupling enhanced growth by nitrogen and hydrogen plasma of carbon nanotubes

Abstract

The mechanism behind the growth of carbon nanotubes (CNTs) based on the microwave plasma chemical vapour deposition (MPCVD) method is clarified. Herein, the influence of nitrogen (N2) and hydrogen (H2) concentration/flux on the CNT growing process has been systematically studied. First-principles calculations indicate that the reaction energy of the dissociative carbon obtained from CH4 is significantly decreased when plasma is utilised. Values of 2.87 (or lower) and 0.18 eV with the introduction of N plasma and H plasma, respectively, are lower than the 18.31 eV obtained for CH4 splitting without plasma assistance. This indicates that N plasma and H plasma could promote the growth of CNTs. Hence, a novel coupling enhanced mechanism for improved understanding of CNT growth is proposed. For the catalyst activity, N plasma helps to rapidly activate the catalyst, and H plasma maintains the activated state of the catalyst for longer. This model matches well with experimental results. Based on this mechanism, different morphologies of MWCNTs can be modulated, which could serve as a good supporter for sensor materials at room temperature.