Laser Synthesis of Single-wall Carbon Nanotubes Utilizing High Temperature Induction Heating.
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Laser Synthesis of Single-wall Carbon Nanotubes Utilizing High Temperature Induction Heating. T. Gennett1, A.C. Dillon2, J.L. Alleman2, K.M. Jones2, P. A. Parilla2, and M.J. Heben2 1 Department of Chemistry, Rochester Institute of Technology Rochester, NY 14623 U.S.A. 2 National Renewable Energy Laboratory, 1617 Cole Blvd. Golden, CO 80401 U.S.A. ABSTRACT An inductive heating system was used to control the temperature of the target during laser synthesis of SWNTs. The position of the target relative to the heating coil, the type of catalyst metals and the synthesis temperatures were all varied in attempts to gain more control over the types of carbon single wall nanotubes grown. Raman spectroscopy results suggest that narrower diameter distributions are produced when the gas-phase species are rapidly condensed. TEM analysis of the raw soot shows that many tube ends are present and that the tubes are short due to incomplete growth. This investigation shows that it is possible to gain further control over SWNT diameter distributions through fine control of the reaction environment made possible with inductive heating. INTRODUCTION Over the past several years a large number of synthetic procedures for the production of Single-Wall Carbon Nanotubes (SWNTs) have been described in the literature. The resultant materials, regardless of the specific synthetic technique, are always a heterogeneous mixture of various diameters and types of SWNTs. The distribution of tube diameters and helicity affect several observed physical, electrical and mechanical properties of the nanotube sample. Therefore, in order for a more specific understanding and subsequent commercial exploitation of SWNT materials, synthesis of “diameter-pure” and "chirality-pure" nanotubes is essential. This article describes experiments that explore the possibility of producing narrow SWNT diameter distributions with fine control of the temperature of the gas-phase species with inductive heating. EXPERIMENTAL The synthesis technique was similar to the pulsed laser vaporization technique described by Guo et al [1]. In this synthesis however single pulses of either Nd:YAG (1064 nm) or Alexandrite (755nm) laser light were employed to synthesize the carbon nanotubes. The pressed graphite target contained a variety of metal dopants; 0.6 at % Co/Ni; 1.2 at % Pd/Rh; or 1.2 at % Pt/Rh. In the current apparatus, shown in figure 1, an induction heater (IH) replaced the hinged furnace. A 5 kW self-tuning Radyne Induction heater was used to heat a 3.8 cm diameter graphite susceptor. The front end of the susceptor was machined to accept the 2.54 cm diameter, 1 cm thick pressed graphite target. The susceptor with target was placed on fiberfax mat insulation to limit radiant heat from the susceptor and insulate the quartz tube. The quartz tube was slid through the induction coil and then mounted into the O-ring sealed end fixtures.
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Figure 1. Apparatus for the synthesis of single wall carbon nanotubes utilizing inductive heating and laser vaporization of a metal do
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