Nanorods are understood as meaning both solid and hollow rod-shaped particles. Nanorods, if they are not hollow, are also called nanosticks. Otherwise, they are nanotubes. Nanotubes formed of carbon, that is, carbon nanotubes, are referred to as CNTs (carbon nanotubes) for short.
Carbon nanotubes have a variety of technical application potentials; an overview and outlook is summarized in: Kanian Balasubramanian, Marko Burghard, “Funktionalisierte Kohlenstoff-Nanoröhren [in English: Functionalized carbon nanotubes]”, Chemie in unserer Zeit, 2005, Vol. 39, pp. 16 to 25 and in: Andreas Hirsch, “The era of carbon allotropes”, Nature Materials, 2010, vol. 9, pp. 868-871. Carbon nanotubes are approximately cylindrical molecules whose walls, like the planes of graphite, consist of carbon, the carbon atoms on the lateral surface having a honeycomb-like structure with hexagons. Carbon nanotubes can be open or closed tubes; in the case of closed carbon nanotubes their closed ends differ from the graphite structure of the cylindrical walls and transition into a fullerene structure. In the case of carbon nanotubes, one carbon atom is covalently linked to three further carbon atoms on the lateral surfaces and at closed ends. In the case of open carbon nanotubes, the carbon atoms at the respective end are covalently linked to less than three bonding partners. The diameter of the carbon nanotubes is in the range of 0.3 to 200 nm. Lengths of several millimeters for single carbon nanotubes and up to 20 cm for bundles of carbon nanotubes have already been achieved.
In carbon nanotubes, other free atoms and molecules may be included, for example noble gases, metal atoms and metal clusters, carbon dioxide and alkanes. Multi-walled carbon nanotubes comprise those carbon nanotubes in which at least one additional carbon nanotube is included as a separate molecule. Carbon nanotubes may also have heteroatoms, especially nitrogen, and be functionalized with a variety of inorganic and organic radicals.