Single-Wall Carbon Nanotubes Synthesis by Means of UV Laser Vaporization: Effects of the Furnace Temperature and the Las
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Single-Wall Carbon Nanotubes Synthesis by Means of UV Laser Vaporization: Effects of the Furnace Temperature and the Laser Intensity Processing Parameters N. Braidy1, M.A. El Khakani1, G.A. Botton2 1 Institut National de la Recherche Scientifique, INRS-Énergie et Matériaux, 1650 Lionel-Boulet, Varennes, PQ, J3X 1S2, Canada. 2 Materials Technology Laboratory, CANMET, 568 Booth Street, Ottawa, ON, K1A 0G1, Canada.
ABSTRACT 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).
INTRODUCTION Since the first demonstration in 1995 of the use of a Q-switch Nd:YAG laser as a new alternative to synthesize single-wall carbon nanotubes [1], the field of laser synthesis of carbon nanotubes continues to attract great interest for either fundamental or applications purposes. Indeed, the laser vaporization technique stands out by its capacity to produce exclusively singlewall nanotubes (SWNTs) at the highest yield ever reported (~80 %) [2]. Focus has been put on the study of the effect of many processing parameters in order to optimize the technique. For example, the influence of the furnace temperature was investigated for dual pulse Nd:YAG laser [3] and pulsed CO2 laser [4] to conclude that a higher furnace temperature leads not only to the production of a higher fraction of SWNTs (against other carbonaceous species) but also to a preferential growth of SWNTs of larger diameters. Other studies have reported on the influence of laser intensity for single and/or dual pulse Nd:YAG laser and established the existence of an optimal laser intensity at which SWNTs are preferentially grown [5, 6]. On the other hand, all the research reported to date on the laser synth
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