A new method for synthesizing single-wall carbon nanotubes

Abstract

Since their initial discovery [1], carbon nanotubes have been attracting much interest because of their properties and potential applications in high-performing nanoscale materials and electronic devices [2–8]. Further progress toward the use of nanotubes as practical materials will require the elimination of defects and other reaction products (such as amorphous carbon and catalyst particles). Defect-free nantotubes (nonspherical fullerenes) are expected to have remarkable mechanical properties, especially electronic and magnetic properties. Recently, the synthesis of singlewalled nanotubes (SWNTs) [9, 10] in the presence of catalysts has instilled a new impetus into the study of carbon nanotubes because SWNTs are expected to be much more free of defects than the multi-walled nanotubes [11, 12]. Indeed, in the extensive examination of transmission electron micrographs, no defects in SWNT have been found. Because SWNT represents the idealization of nanotube materials, many papers are focused on the synthesis and physical properties of SWNT as well as the growth model [9–11, 13–20]; besides, a few simulations have also been done [21–24]. Up to now, carbon arc and laser vaporization are generally considered as the main methods to produce SWNTs and in each method, a small amount of catalysts was added to the carbon target. Many different catalysts, such as transition metals Fe, Co, Ni and Cu, lanthanide metals Gd, Y, and La, as well as several mixed catalysts, have been selected to prepare the carbon nanotubes [20]. However, it is not clear why the growth of single-walled nanotubes, in contrast to that of the multi-walled nanotubes, generally requires the presence of metal catalysts. Now looking for new methods for synthesizing SWNTs would be an interesting activity for further understanding the physical mechanism of SWNT formation. Recently, we observed that SWNTs were formed when nanofibers (whose diameters are in the range of 70–100 nm), prepared by the catalytic decomposition of hydrocarbons on small metal particles, were annealed under high pressure. In this letter, we study the microstructural transformation of carbon nanofibers under 5.5 GPa pressure and report a new method for