326 JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY J. Nanosci. Nanotech. 2004, Vol. 4, No. 4 © 2004 by American Scientic Publishers 1533-4880/2004/04/326/020/$17.00+.25 doi:10.1166/jnn.2004.069 * Author to whom correspondence should be addressed. RESEARCH ARTICLE 1. INTRODUCTION Carbon nanotubes were discovered by Iijima, 1 using the arc discharge method to synthesize fullerenes. They were multi-walled nanotubes, but soon it was realized that single-walled carbon nanotubes (SWNTs) could be syn- thesized in the presence of transition metal catalysts. 2, 3 SWNTs are promising materials because of their outstand- ing mechanical, electrical, and thermal conductivity prop- erties; therefore, great effort has been devoted to optimizing their synthesis conditions. In addition to the arc discharge method, 4 the laser ablation method, 5 and solar energy fur- nace method 6 are all high temperature processes (2500– 5000 °C) with which carbon and metal catalysts are obtained by evaporation of graphite and metal powders. Concomitantly, catalytic methods were introduced with which the carbon source is obtained from the decomposi- tion of hydrocarbons (methane, ethylene, etc.) or CO on supported metal particles 7–9 or on metal particles directly injected into the reaction chamber. 10 The catalytic methods operate at low temperature (800–1200 °C). Table I shows a comparison of the various results obtained on supported metal catalysts. It can be seen that the presence of transition metals is indispensable for the production of SWNTs. We shall come On the Growth Mechanism of Single-Walled Carbon Nanotubes by Catalytic Carbon Vapor Deposition on Supported Metal Catalysts J. B. Nagy, a, * G. Bister, a, b A. Fonseca, a D. Méhn, a Z. Kónya, b I. Kiricsi, b Z. E. Horváth, c and L. P. Biró c a Nuclear Magnetic Resonance Laboratory, Facultés Universitaires Notre-Dame de la Paix, Namur, Belgium b Applied and Environmental Chemistry Department, University of Szeged, Szeged, Hungary c Research Institute for Technical Physics and Materials Science, Budapest, Hungary A comprehensive kinetic study was performed to throw light on the formation mechanism of single walled carbon nanotubes (SWNTs) in chemical vapor deposition processes. SWNTs were synthe- sized by catalytic decomposition of methane or ethylene on supported transition metal catalysts. Kinetic curves (the amount of SWNT as a function of time) were obtained as a function of the nature and the preparation of the supported catalysts, temperature, the uxes of the gases (the reagent hydrocarbon and the carrying gas), and the partial pressure of the hydrocarbon. The nal products were characterized by transmission electron microscopy, Raman spectroscopy, chemical analysis, and thermogravimetric measurements. The fundamental factors determining the SWNT formation are discussed in detail, taking into consideration several observations from the literature as well. Keywords: Nanotube, Growth, Synthesis, Mechanism, Catalyst, Catalytic Chemical Vapor Depo- sition, Carbon. back to their role later in the discussion on the mechanism of SWNT formation. In most cases the supports used are Al 2 O 3 , SiO 2 , SiO 2 / Al 2 O 3 , MgO, Y zeolite, CaSiO 3 , or ZrO 2 . For special appli- cations, metal lms were also used. 32 The pyrolysis of tripropylamine occluded in the AlPO 4 -5 linear channels merits particular attention. 30, 31 Indeed, SWNTs having the smallest diameter known of 0.4 nm could be obtained, because the diameter was imposed by the diameter of the channel (0.73 nm). It has to be emphasized that a strong metal support interaction is present in most of the systems studied. The methods of preparation are quite varied. In many cases, however, the simplest method of direct impregna- tion by precursor solutions was used. The main purpose is the highest dispersion for metal particles. Indeed, the dia- meter of isolated nanoparticles directly inuences the diameter of the SWNTs. 8, 9, 21 In the formation of a solid solution by combustion syn- thesis, the metal ion precursor is also highly dispersed: ¬ - Al 222 x Fe 2x O 3, 11–14 Mg 0.8 M y M9 2 Al 2 O 4 with M or M95 Fe, Co, or Ni, 22 or Mg 0.9 Co 0.1 O 24,25 or Mo x Co y Mg 1 2x 2y O. 28 In these cases a direct inorganic SWNT composite can be obtained. Special cases include the formation of a LaFeO 3 per- ovskite phase, 36 the mechanical mixing of the metal pow- der and the support, 41 spin coating of Fe/Mo on Pb(Zr 0.5