Carbon goes long

Super-long carbon nanotubes can be grown using an optimized chemical vapour deposition synthesis

Credit: © 2006 Japan Society of Applied Physics

Extremely long, well-aligned bundles of carbon nanotubes (CNTs) are mechanically robust and show promise for use as electrical connections and lightweight fibres. Until now, however, attempts to increase the length of CNT structures have involved the synthesis of short tubes that can then be processed into longer fibres using, for example, a spinning technique. A simple and reproducible means of producing long strands of high-purity, aligned CNTs is still elusive.

Now, Supriya Chakrabarti and colleagues¹ at Osaka Science and Technology Center, Taiyo Nippon Sanso Co., and Osaka Prefecture University, Japan, have synthesized aligned ‘super-long’ CNTs on Fe/Al₂O₃/SiO₂/Si substrates. By optimizing the widely used catalytic chemical vapour deposition method, it was possible to produce CNTs with lengths of up to 7 mm after 12 hours of deposition. Precise control of the flow rates of the synthesis gases (hydrogen, water and ethylene) prevented the accumulation of unwanted products on the Fe catalyst surface. This increased the lifetime of the catalyst and prolonged the growth time of the CNTs.

Transmission electron microscope (TEM) images showed the CNTs to be mainly double-walled structures, although some single- and multiwalled nanotubes were also present. Moreover, TEM studies confirmed that the brush-like arrays of CNTs are formed free of metallic particle impurities.