The catalytic vapour phase deposition of carbon was reported in 1952 and 1959, but it was not until 1993 that carbon nanotubes were formed by this process. During CVD, a substrate is prepared with a layer of metal catalyst particles, most commonly nickel, cobalt, iron or a combination.
The metal nanoparticles can also be produced by other ways, including reduction of oxides or oxides' solid solutions.
The diameters of the nanotubes that are to be grown are related to the size of metal particles.
CVD is the most widely used method for the production of carbon nanotubes.
For this purpose, the metal nanoparticles are mixed with a catalyst support such as MgO or Al2O3 to increase the surface area for a higher yield of the catalytic reaction of the carbon feedstock with the metal particles.
One issue in this synthesis route is the removal of the catalyst support via an acid treatment, which sometimes could destroy the original structure of the carbon nanotubes.