Carbon 40 (2002) 417–423 Single-wall carbon nanotubes with diameters approaching 6 nm obtained by laser vaporization a, b b a * Sergei Lebedkin , Peter Schweiss , Burkhard Renker , Sharali Malik , c c c a,c Frank Hennrich , Marco Neumaier , Carsten Stoermer , Manfred M. Kappes a ¨ Forschungszentrum Karlsruhe, Institut f ur Nanotechnologie, D-76021 Karlsruhe, Germany b ¨ ¨ Forschungszentrum Karlsruhe, Institut f ur Festkorperphysik, D-76021 Karlsruhe, Germany c ¨ ¨ Institut f ur Physikalische Chemie, Universitat Karlsruhe, D-76128 Karlsruhe, Germany Received 20 February 2001; accepted 28 April 2001 Abstract Single-wall carbon nanotubes (SWNTs) with large diameters from 2 to 5.6 nm were prepared by pulsed laser vaporization of carbon rods doped with Co, Ni and FeS in an atmosphere of Ar:H . The SWNT material was characterized by SEM, 2 HRTEM, Raman, IR, UV–VIS–NIR absorption spectroscopy and thermogravimetric analysis.  2002 Elsevier Science Ltd. All rights reserved. Keywords: A. Carbon nanotubes; B. Laser irradiation; C. Electron microscopy, Raman spectroscopy, Thermal analysis (DTA and TGA) 1. Introduction composition of the target / process gas. For example, laser vaporization of carbon doped with Pd, Rh is known to The established methods for the preparation of SWNTs produce smaller diameter nanotubes [9]. Numerous studies such as laser vaporization of C:Ni:Co targets [1,2] and of the effect of various additives on the yield and morphol- electric arc vaporization of C:Ni:Y rods [3] in an inert gas ogy of nanotubes have been performed using electric arc atmosphere (Ar) as well as pyrolysis of CO [4] and vaporization, which was historically the first method to hydrocarbons (CH ) [5–7] on metal catalyst nanoparticles produce SWNTs [10,11]. It was found that the addition of 4 produce carbon tubes with typical peak diameters of |1.2– some non-catalytic elements (e.g., S, Bi, Pb) to Ni, Co 1.7 nm. Among these preparative methods, laser vapor- promoted growth of nanotubes with large diameters up to ization remains the most advantageous with regard to high |6 nm [12,13]. On the other hand, a solar oven vapor- yield of SWNTs, homogeneity of the product, and precise ization of carbon doped with Ni, Co and S yielded SWNTs control of process parameters. The diameter distribution of with a broad diameter distribution, including a substantial SWNTs produced by this method is particularly narrow fraction of nanotubes with diameters smaller than |1 nm and within |1.2–1.5 nm. The preparation of SWNTs of as judged from the Raman spectra [14]. Hydrogen can also similarly high quality but with larger diameters would be influence the growth of nanotubes: SWNTs with diameters of great interest. They can be used for comparative studies around 2 nm have been produced from graphite mixed of the properties of SWNTs vs. tube diameter and as with Co, Ni and FeS and vaporized by electric arc in a templates for nanowires and other nanostructures. pure hydrogen atmosphere [15]. The diameter distribution of SWNTs produced by laser In this work, we have studied the effect of hydrogen (as vaporization is affected by the process temperature and gas aH admixture to Ar) and sulfur (as a FeS additive to 2 pressure, however the variation is limited by a decrease in carbon targets) on SWNTs produced by pulsed laser the nanotube yield [8]. A larger effect on the diameter vaporization of carbon targets doped with Ni, Co metal distribution can be achieved by changing the chemical catalysts. Our results show that the introduction of hydro- gen, sulfur or, particularly, both leads to the efficient formation of SWNTs with large diameters approaching 6 *Corresponding author. Fax: 149-7247-826368. E-mail address: lebedkin@int.fzk.de (S. Lebedkin). nm. The SWNT materials have been characterized by 0008-6223 / 02 / $ – see front matter  2002 Elsevier Science Ltd. All rights reserved. PII: S0008-6223(01)00119-1