Monodisperse carbon nanopearls in a foam-like arrangement: a new carbon nano-compound for cold cathodes

This paper reports the low cost, high yield chemical vapor deposition synthesis of a potentially novel carbon nanomaterial using nickel nanocluster-catalysed dissociation of acetylene at 700 degreesC. The resulting 'carbon nanopearls' are 150 nm in diameter with similar to 85% monodispersity, with a solid structure composed of both amorphous and nanocrystalline (similar to 2 nm repeat unit) regions. The nanopearls form 3D space-filling 'strings' which give rise to a macroscopic foam-like appearance. The nanopearls have been characterized using scanning electron microscopy, high resolution transmission electron microscopy, X-ray microdiffraction, Raman spectroscopy and energy dispersive X-rays. A mechanism for the formation of the nanopearls is proposed based on concentric layers of similar to 4 x 4 nm graphitic flakes. The small radius of curvature of each nanopearl and the corrugation at the atomic scale of the surface resulting from the unclosed graphitic flakes result in excellent field emission properties. It has been demonstrated that a film of conditioned carbon nanopearls exhibits Fowler-Nordheim field emission behavior, with currents of up to 50 muA readily obtainable under continuous emission in moderate vacuum. It is proposed that such emitters would provide significantly higher yield, uniform emission characteristics than non-oriented films of carbon nanotubes due to the reproducibly high density of nanopearl emitter sites. (C) 2004 Elsevier B.V. All rights reserved.