Two main methods of producing nanotubes involve a plasma state. In one, the plasma is created by an arc discharge, and in the other by laser ablation of a graphite rod. In both cases the presence of metallic catalysts, such as cobalt, iron, or nickel, is essential. On the basis of observation and theoretical calculations, researchers believe that the catalyst atoms act to form the nanotubes by attaching themselves to the growing edge of the tube. These atoms scoot round and round as carbon atoms attach to the edge, which keeps the tube open and ensures the formation of a regular hexagonal structure.Laser ablation method uses a high-power laser to vaporise a graphite source loaded with a metal catalyst. The carbon in the graphite reforms as predominantly single-wall nanotubes on the metal catalyst particles. Arc discharge method involves an electrical discharge from a carbon-based electrode in a suitable atmosphere to produce both single and multi-wall tubes of high quality but in low quantities.Chemical vapour deposition (CVD) method uses a hydrocarbon feedstock to react with a suitable metal-based catalyst in a hot furnace to ‘grow’ nanotubes which are subsequently removed from the substrate and catalyst by a simple acid wash.