The low-temperature synthesis (500-560 degrees C) of carbon nanotubes (CNTs) on a triple-layered catalyst, Al/Fe/Mo was performed using complex hydrocarbon radicals which were produced from pyrolysis of C(2)H(2). These radicals were produced using a high-temperature heater (similar to 830 degrees C), but the substrate where the CNTs were grown was placed on a thermal insulator. This then enabled the substrate to be at a much lower temperature (500-560 degrees C). A simulated temperature distribution inside the chamber was also used to describe this low-temperature configuration. The synthesis of CNTs relies on the thermal dissociation and dissociative recombination of C(2)H(2) for the formation of complex high-order radicals (i.e. C(6)H(9), C(5)H(9), and C(6)H(13)), and their presence was confirmed by in-situ mass spectroscopy. To explain this, a simple gas-phase radical chain process and a growth model are presented. (C) 2009 Elsevier B.V. All rights reserved.