Synthesis of aligned carbon nanotubes by DC plasma-enhanced hot filament CVD

Vertically aligned carbon nanotubes (CNTs) films have been prepared by a direct current plasma-enhanced hot filament chemical vapour deposition method. The growth of multi-walled carbon nanotubes on metal (Fe, Co, Ni) precoated silicon substrate are studied between 500 and 1000 °C using gas mixtures of methane, hydrogen and argon. The influence of substrate pre-treatment, substrate voltage and deposition temperature on the structure and the alignment of the CNTs are discussed. In dependence on thickness of the thin metal layers, thermal pre-treatment or hydrogen plasma etching and plasma parameters during the deposition process different carbon nanostructures, especially regarding tube diameter, morphology and arrangement could be proved. Transmission electron microscopy images of isolated tubes showed an imperfectly trained tubular structure of graphite shells, formed as ‘bamboo’-like shapes with partly crystalline metal droplets on the tip. Because the alignment of the tubes is induced by the discharge voltage and the electrical field, the characteristic plasma parameters as plasma potential, electron energy and electron density, measured by Langmuir probe investigations were discussed.