Abstract: A process for preparing carbon nanotubes comprising locating a substrate (1) capable of supporting carbon nanotube growth in a localised heating zone within a reaction chamber (7), said localised heating zone being provided by a heating element (2) located within the reaction chamber (7), passing a gaseous carbonaceous material into the reaction chamber (7) such that the gaseous material passes over and contacts the substrate (1) in the localised heating zone, whereby the gaseous material undergoes pyrolysis under the influence of the heat to form carbon nanotubes on the substrate (1). Embodiments of the process prepare multilayer carbon nanotubes and hetero-structured multilayer carbon nanotube films.