Effect of CN and CH radicals on diamond and carbon nanotubes growth in MECVD

Summary form only given, as follows. Diamond films and carbon nanotubes can both be synthesized by microwave-plasma enhanced chemical vapor deposition (MECVD) technology. When a mixture of methane, nitrogen and hydrogen is used to generate the discharge, either diamond or graphite phases, or both, can be formed on the substrate. Using optical emission spectra (OES), we have found a strong correlation between the type of active species (CN and CH) and the phase of growth on the substrate. In particular, in the case of carbon nanotube growth, intensity ratio of CN and C/sub 2/ radicals was found to be closely related with morphology, microstructure and graphitization degree of the samples prepared at different CH/sub 4//N/sub 2/ ratio. Carbon nanotubes show well aligned from SEM picture at about 20% CH/sub 4/ ratio, longer in length and denser in distribution indicate high growth rate. "Nanobell" structure from TEM results is polymerized when nitrogen dominates in the mixing gas and the length and thickness of the nanobells varied with the CH/sub 4/ ratio. Raman spectra show better graphitization of sample at low CH/sub 4/ ratio and more amorphous structures form when CH/sub 4/ ratio increase. Relative concentration of CN to C/sub 2/ radicals benefits to the alignment of nanotubes and is disadvantageous to the graphitization of samples. However, in the case of diamond growth, as indicated by optical emission spectra, CH radicals play key role in the diamond phase formation process. The effect of these radicals in plasma to the formation of diamond and graphite phase is briefly discussed.