Abstract Submitted to the    NANOTUBE'04 Conference:

Experiments and modelling have been undertaken to clarify the role of metal catalysts during single-wall carbon nanotube formation [1]. A reactor has been developed for synthesis by continuous CO2-laser vaporisation of a carbon-nickel-cobalt target in laminar helium flow. The laser induced fluorescence technique [2] is applied for local probing of gaseous Ni, Co and C2 species throughout the hot carbon flow of the target heated up to 3500 K. A rapid depletion of C2 in contrast to the spatial extent of metal atoms is observed in the plume, asserting that C2 condenses earlier than Ni and Co atoms. The depletion is even faster when catalysts are present, suggesting that an interaction between metal atoms and carbon dimers takes place in the gas. Two methods of modelling are used: a spatially 1-D calculation developed originally for the arc process [3], and a zero-D time dependent calculation, solving the chemical kinetics along the streamlines [4]. The latter includes Ni cluster formation. The peak of C2 density is calculated close to the target surface where the temperature is the highest. In the hot region, C3 is dominant. As the carbon products move away from the target and mix with the ambient helium, they recombine into larger clusters as demonstrated by the peak of C5 density around 1 mm. The profile of Ni-atom density compares fairly well with the measured one. The early increase is due to the drop of temperature, and the final decrease beyond 6 mm results from Ni particle formation at the eutectic temperature (~1600 K).

[1] J.Gavillet et al., J. Nanosci. Nanotech. 4, (2004).
[2] Dorval et al. J. Nanosci. Nanotech. 4, (2004).
[3] S. Farhat et al., J. Nanosci. Nanotech. 4, (2004).
[4] C.D. Scott, J. Nanosci. Nanotech. 4 (2004).