Tailoring Carbon Nanoclusters to Desired Morphologies
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Tailoring carbon nanoclusters to desired morphologies Jun Jiao and Supapan Seraphin Department of Materials Science and Engineering, University of Arizona, Tucson, Arizona 85721 (Received 23 January 1998; accepted 16 April 1998)
The preparation and structural characterization of carbon nanoclusters of different morphologies produced by three different methods and under a variety of conditions is reported. In a comparative manner, the growth phenomena and structural properties of carbon nanoclusters are investigated as synthesized by (a) the high temperature (,3000 ±C) and high carbon-content process of the conventional arc-discharge, (b) the high temperature but low carbon-content process of the modified arc-discharge, and finally (c) the relatively low temperature (,500 ±C) process of Ni catalytic disproportionation of carbon monoxide.
I. INTRODUCTION
Carbon nanoclusters have attracted attention in recent years not only for their small dimension and unique morphologies, but also for their potential of applications in various technologies. Following the discovery of a method for the preparation of fullerenes in macroscopic quantities by Kr¨atschmer and Huffman,1 the field experienced another surge of interest when Iijima2 reported on a nonspherical form of carbon-based materials, the multiwalled nanotubes. Unlike the spherical fullerenes extracted from the soot, these nanotubes were retrieved from the negative electrode of an arc-discharge plasma in the reactor previously employed for the production of fullerene soot.3 Soon thereafter, several reports confirmed that the same types of tubular and spherical morphologies can be found in the deposits of the catalytic decomposition of different hydrocarbons for which early reports can be traced back to the year of 1890.4 However, due to their nanometer dimension as well as their delicate internal structure, technological promise could not be realized until high resolution electron microscopes became available.5 The cylindrical configurations were stacked concentrically by curved graphitic sheets, separated by the same distance of 0.34 nm characteristic for the separation of the basal graphitic planes. Theoretical calculations carried out by several research groups have studied the electronic properties of nanotubes.6 – 8 In particular, Hamada et al.,9 using tight-binding band-structure calculations, predicted striking variations in electronic transport from metallic to semiconducting with narrow and moderate band gaps, depending on the structure of the tube. Foreign materials could be encapsulated into the hollow cores of the multiwalled tubes, thus not only promising materials of unique properties due the nanometer size, but also suggesting obvious applications such as nanowires and composites.10,11 Ajayan and Iijima12 have actually filled liquid lead into nanotubes by capillary 2438
http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 9, Sep 1998
Downloaded: 13 Apr 2015
suction. Seraphin et al.13,14 have succee
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