Abstract Submitted to the NANOTUBE-99 Workshop:

Lack of experimental evidence for the nanotube growth has hindered elucidation of the tubule formation. High growth temperature, a very short period of time of formation, and presence of metal catalyst make such experiments difficult. To overcome the problem we have utilized two direct methods, shadowgraphy and emission imaging- spectroscopy of the laser plume, for the study of growth of graphitic structures which are produced by CO₂ laser ablation of graphite. The use of CO₂ laser has an advantage over the conventional Nd-YAG laser; first, its pulse width is ~20ms compared with ~10ns for the YAG laser, which enables us to visualize development of the laser plume over a graphite target in the shadowgraphy technique through a high speed video-recorder. Second, the laser intensity of ~105W/cm² is about a right input power to form a plume which is detected by our video-camera, whereas the Nd-YAG laser intensity of ~109W/cm² is too high. The emission imaging spectroscopy can provide with spatial and temporal distribution of light emission from the laser plume, where black-body radiation and C₂ dimers emission are dominant.

The dynamic observation of the laser plume tells us to some extent where and when the graphitic structures are formed during the laser ablation. As an example of a CO₂ laser ablation product, which are formed abundantly under a specific condition, we introduce SWCNTs with corn-shape caps which aggregates into a spherical particle of ~80nm in diameter. We call this tubules a single-wall carbon 'NANO-HORN'. The nano-horns are formed at room temperature and without metal catalyst unlike single-wall carbon nanotubes, so that the formation of such a nano-horn is much simpler than that of SWCNTs.

Another experimental fact that the CO₂ laser ablation at room temperature can produce SWCNTs is also worth to consider of the formation of the SWCNTs.

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