Formation of single-wall carbon nanotubes: Comparison of CO2 laser ablation and Nd : YAG laser ablation

Investigating the formation of single-wail carbon nanotubes (SWNTs) from a target composed of graphite, Ni, and Co, we compared the use of a pulsed CO 2 laser (pulse width of 20 ms, laser-power density of 0.1 MW/cm(2)) with th e use of a pulsed Nd:YAC laser (pulse width of 5-7 ns, laser-power density of 4 GW/cm(2)). When the total irradiation energy was 2 kW/cm(2) for the CO 2 laser ablation and 2.4 kW/cm(2) for the Nd:YAC laser ablation, SWNTs coul d be formed at 300 K by CO2 laser ablation, whereas the lowest temperature at which they could be formed by Nd:YAG laser ablation was about 1170 K. Th e lowest pressure allowing SWNT formation was 50 Torr for CO2 laser ablatio n and 200 Torr for Nd:YAG laser ablation. The structures of carbonaceous de posits and of the target surfaces indicated that CO2 laser ablation resulte d in carbon being emitted from the edges of or defects in the graphite part icles and most of the Ni and Co being emitted from the target. Pulsed Nd:YA G laser ablation, on the other hand, has been reported to result in graphit e melting and mixing with Ni and Co on the target surface, the mixture bein g expelled from the target surface, and clumps of Ni and Co remaining on th e target surface after the laser ablation, We think these differences are d ue to the different laser-power densities and pulse widths.