First observation of single-wall and multi-wall nanotubes
wish to revisit a statement in my initial annotation the Guest
Editorial by Marc Monthioux and Vladimir L. Kuznetsov: Who should be
given the credit for the discovery of carbon nanotubes?, Carbon 44, 1621 (2006); Highlights in Small Systems, http://jsmallsystems.org/hss/2006/1. I would like to expand on my suggestion that the authors made "several inaccurate technical statements" in their Guest Editorial.
* Stability of wide-diameter single-wall nanotubes.
Referring to calculations of Jerry Tersoff and Rod Ruoff, the authors of the Guest Editorial suggest that wide-diameter single-wall nanotubes (SWNTs) should be unstable. This is only true for long, unsupported nanotube segments with cylindrical symmetry. Of course, wide SWNTs are likely to collapse to a ribbon, which still should be considered a (deformed) SWNT, and still should be stable. Ribbons have been reported by Alex Zettl some time ago, and may form preferentially under specific synthesis conditions, as the authors suggest. Also the tube shown in Fig. 1 of the Guest Editorial may be a single-wall carbon nanotube that collapsed to a ribbon.
Furthermore, a wide diameter SWNT is expected not to collapse if it is supported from the outside. This is surely true for the core nanotube inside a multi-wall nanotube (MWNT), which typically has a large diameter. This is also likely true for the core tube of a MWNT, which is locally thinned down to a SWNT. Such a structure contains a short tube segment that is missing the outer walls, providing external support and preventing collapse. This is an alternative interpretation of Fig. 1, representing a short single-wall carbon nanotube segment.
Finally, the authors of the previous annotation to the Guest Editorial suggest that re-evaluation based on the original film indicates that the diameter of the central part of the nanotube, depicted in Fig. 1, should be 3.3 nm and not 5 nm, as suggested in the Guest Editorial.
* First observation of multi-wall nanotubes.
Referring to Fig. 2 in their Guest Editorial, the authors suggest that the 1952 observation of filamentous carbon by electron microscopy is equivalent to "the discovery of carbon nanotubes". I believe that the entire Nanotube Community is impressed by the early observation of hollow, tubular nanostructures, which are strongly reminiscent of multi-wall carbon nanotube In fairness, we should note that the first generation of electron microscopes was unable to resolve individual graphene layers. Consequently, and thus could not distinguish between a set of nested graphitic cylinders (Sumio Iijima, "Helical microtubules of graphitic carbon", Nature 354, 56 (1991)), a continuous graphene monolayer rolled up to a croll, or any other arangment of carbon atoms.
The scroll and the multi-wall nantoube allotropes are fundamentally different morphologically and in their electronic structure. I believe that both forms are similarly stable and have a similar internal diameter (Savas Berber and David Tomanek, Stability differences and conversion mechanism between nanotubes and scrolls, Phys. Rev. B 69, 233404 (2004)). I believe that they may even coexist within a single tube (J. Gerard Lavin, Shekhar Subramoney, Rodney S. Ruoff, Savas Berber and David Tomanek, Scrolls and Nested Tubes in Multiwall Carbon Nanotubes, Carbon 40, 1123 (2002)).
Sumio Iijima denied any possibility of scrolls based on his high-resolution images. Radushkevich and Lukyanovich did not have the tools to do so in 1952. Since Radushkevich and Lukyanovich do not claim a structure consisting of (nested, but disconnected) graphitic cylinders, their observation should not be considered eqivalent to the discovery of (multi-wall) carbon nanotubes.