A method for making an array of carbon nanotubes includes the steps of: (a) providing a substrate with a film of catalyst provided thereon; (b) disposing the substrate in a reaction chamber; (c) introducing a carrier gas into the reaction chamber and heating the reaction chamber to a predetermined temperature; (d) introducing a carbon source gas and a hydrogen gas into the reaction chamber separately and simultaneously; the hydrogen gas being introduced such that the hydrogen gas has less of a distance to travel in the reaction chamber than does the carbon source gas to reach the substrate; and (e) growing the array of the carbon nanotubes from the substrate.