Gas-phase and sample characterizations of multiwall carbon nanotube growth using an atmospheric pressure plasma

Multiwall carbon nanotubes (CNTs) are synthesized using an atmospheric pressure rf plasma jet, with helium feed gas and acetylene gas as the precursor. The nanotubes are grown on a substrate with a thin catalyst (iron) film, with the substrate placed downstream from the plasma on a copper hot plate. In situ Fourier transformed infrared spectroscopy indicates an increase in gas temperature and a decrease in the density of the acetylene molecules at higher plasma powers. The helium metastables in the plasma break the C-H bonds in acetylene, causing molecular dissociation. It is apparent that the resultant formation of unsaturated carbon bonds causes taller and more graphitized CNT films to grow, as evident from scanning electron microscopy and Raman analyses of the samples. However, at higher substrate temperatures, taller and better quality films are obtained due to enhanced catalytic activity on the substrate surface