methods and processes for synthesizing single - wall carbon nanotubes are provided . a carbon precursor gas is contacted with metal catalysts deposited on a support material . the metal catalysts are preferably nanoparticles having diameters less than about 3 nm . the reaction temperature is selected such that it is near the eutectic point of the mixture of metal catalyst particles and carbon . further , the rate at which hydrocarbons are fed into the reactor is equivalent to the rate at which the hydrocarbons react for given synthesis temperature . the methods produce carbon single - walled nanotubes having longer lengths .