The production of high-purity multi-wall carbon nanotubes (MWNTs) without metal catalysts was produced using radio-frequency plasma. The MWNTs had diameters of about 5 nm, with the innermost tubes having a diameter of 0.4 mn, the smallest value possible for a single-wall carbon nanotube. Two types of aggregates were obtained, depending on the conditions of formation: moss-like aggregates (diameter: about 1 mum) and long bundles (length: 10 mum, diameter: 100 um). The MWNTs in the moss-like aggregate, referred to as acute MWNTs, had tips with a cone angle of 19.2degrees. (C) 2002 Published by Elsevier Science B.V.