Three DC plasma processes in a hot filament reactor were developed to synthesize nanostructured carbon films: (1) pure hydrogen plasma treatment of diamond films pre-coated on silicon substrate, (2) plasma-enhanced hot filament chemical vapor deposition (HFCVD) with a gas mixture of hydrogen and methane and (3) graphite etching in a pure hydrogen plasma. Highly aligned diamond nanocone films were synthesized on silicon substrates pre-coated with diamond films in all three processes. When the silicon substrates were predeposited with sparsely distributed diamond particles, diamond and graphitic nanocones were grown simultaneously on substrate areas with and without pre-deposited diamond particles, respectively in the last two processes. All the nanocones have nanometer-size tips and sub micrometer-size roots and are highly aligned with various orientation angles influenced by the direction of the electric field lines near the sample surface. In comparison with the conventional method using a methane and hydrogen mixture, it is found that diamond nanocones synthesized by graphite etching have one order of magnitude higher cone density, lower sp(2) carbon content and grow four times faster. (c) 2005 Elsevier B.V. All rights reserved.