Synthesis of single-walled, bamboo-shaped and Y-junction carbon nanotubes using microwave plasma CVD on low-temperature and chemically processed catalysts

Abstract

The low temperature nucleation and high yield growth of CNTs with their diverse range of layered structures and shapes is of significant interest to the research community in view of obtaining distinctive properties necessary for specific applications. In this regard, several strategies have been employed to control the growth characteristics of CNTs. In the present investigation, the low temperature growth of CNTs has been enabled using CO2 as a suitable oxidizing gas. CNTs have been grown via an optimum etching process conducted under diffuse plasma generated using a specially designed shadow mask assembly that shields the growth surface from direct plasma bombardment, and subsequent abrasive etching by the reactive plasma species. Furthermore, CO2 as a component in the plasma facilitates the elimination of amorphous carbonaceous components from the surface of the CNTs. The growth of narrow CNTs has been achieved via the formation of a low diameter (~20 nm) catalyst comprised of Fe nano-particles grown in a low temperature (10 °C) chemical process under an inert atmosphere via simultaneous aerial oxidation and neutralization in a single step. Further plasma optimization by controlling the MW power has facilitated the growth of CNTs with controlled diameters, wall numbers and different morphologies (e.g., Y-junction and bamboo-shaped MWCNTs, and very low diameter (~1.5 nm) SWCNTs). The tip growth mechanism for CNT nucleation has been established using HR-TEM, in which the Fe catalyst nanoparticles are detected within the top shell of the growing CNTs.