Formation of filled carbon nanotubes and nanoparticles using polycyclic aromatic hydrocarbon molecules

Nanotubes filled with pure Cu and Ge have been formed by using an are discharge with metal/graphite composite anodes in a hydrogen atmosphere. These nanotubes are found in the soot deposited on the chamber walls instead of on the redeposited rod on the cathode as is the case with experiments in He. Since Cu and Ge do not form stable carbide phases, catalyze carbon fiber growth or have significant carbon solubility, a new mechanism is needed to explain the formation of these nanowires. It is proposed that polycyclic aromatic hydrocarbon molecules, produced by the hydrogen are are the precursors to the graphitic layers encapsulating the Cu or Ge nanowire. Direct evidence for this mechanism is given by evaporating pyrene (C16H10) and Cu or Ge together to form filled nanotubes. When evaporating a composite anode in hydrogen using ferromagnetic elements, such as Co, encapsulated nanoparticles are formed instead of nanowires. Encapsulated nanoparticles are also obtained when evaporating pyrene and cobalt, supporting the assertion that PAH molecules are precursors to nanostructure formation. Reasons for the difference between nanoparticle and nanowire formation are attributed to differences in reactivity of the metal with carbon. (C) 1998 Elsevier Science Ltd. All rights reserved.