Synthesis and (some) applications of carbon-nanotube-supported pyrolytic carbon nanocones

Abstract

Graphene-based cones with nanosized apex can be obtained by means of a high temperature pyrolytic carbon depositionprocess using methane and hydrogen as gaseous feedstock and single carbon nanotubes as deposition substrates. Aside thecones, micrometer-sized carbon beads or fibre segments are deposited meanwhile which are a key morphological componentfor allowing handling and mounting the carbon cones and then using them for various applications. Based on both theliterature dealing with pyrolytic carbon deposition processes and experimental observations, a peculiar depositionmechanism is proposed, involving the transient formation of pitch-like liquid phase droplets which deposit onto theindividual carbon nanotubes. In this picture, it is believed that a key parameter is the diameter ratio for the droplets and thenanotubes, respectively. The cone concentric texture and perfect nanotexture are shown by high resolution transmissionelectron microscopy, which allows interesting mechanical and conducting properties to be predicted. Correspondingly,applications of the carbon nanocones as electron emitters for cold-field electron sources on the one hand, and as probes forvarious modes of near-field microscopy on the other hand, have been tested.