Single-Wall Carbon Nanotubes Synthesis by Means of UV Laser Vaporization: Effects of the Furnace Temperature and the Laser Intensity Processing Parameters

Carbon single-wall nanotubes (SWNTs) have been successfully synthesized by means of KrF laser vaporization of a Co-Ni-doped graphite pellet in a flowing argon atmosphere. The effects of two key processing parameters, namely the furnace temperature (in the 25-1150 °C range) and the laser intensity (in the 0.8-4.4 x 108 W/cm2 range), on the yield and the structural characteristics of the carbon SWNTs were investigated. By characterizing the obtained deposits by means of transmission electron microscopy and micro-Raman spectroscopy techniques, we were able to identify a threshold temperature as low as ∼550 °C, below which no carbon SWNTs can be grown. The increase of the furnace temperature from 550 to 1150 °C was found to lead not only to a significant increase in the SWNTs yield but also to the formation of larger SWNTs bundles. Raman analysis have also revealed that the diameter distribution peak shifts from ∼1.05 to ∼1.22 nm as the temperature is raised from 550 to 1150 °C. At the highest furnace temperature of 1150 °C, we also found that a minimum laser intensity of about 1.6 x 108 W/cm2 is required to grow carbon SWNTs by means of the KrF laser. Higher laser intensities have resulted in a higher yield of SWNTs with relatively thicker bundles. Moreover, the increase of the laser intensity was found to promote the growth of 1.22 nm-diameter nanotubes to the detriment of thinner carbon nanotubes (1.05 and 1.13 nm-diameters).