In 1991, Sumio Iijima noticed novel structures in the byproduct soot created during fullerene
production by electric arc-discharge.1 Investigation revealed the tubular nature of these
interesting structures, now known as carbon nanotubes, which have likely existed for years,
but remained undiscovered up to this point. A carbon nanotube may be described as a
graphene sheet rolled up to form a tube, with half-fullerene caps, for closed tubes. The caps
are fairly reactive due to curvature strain, and are readily destroyed during processing,
yielding open tubes.2 Nanotubes are formed in a range of diameters and may be singlewalled
or multi-walled, depending on the reaction conditions.