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

Graphene-based cones with nanosized apex can be obtained by means of a high temperature pyrolytic carbon deposition process using methane and hydrogen as gaseous feedstock and single carbon nanotubes as deposition substrates. Aside the cones, micrometer-sized carbon beads or fibre segments are deposited meanwhile which are a key morphological component for allowing handling and mounting the carbon cones and then using them for various applications. Based on both the literature dealing with pyrolytic carbon deposition processes and experimental observations, a peculiar deposition mechanism is proposed, involving the transient formation of pitch-like liquid phase droplets which deposit onto the individual carbon nanotubes. In this picture, it is believed that a key parameter is the diameter ratio for the droplets and the nanotubes, respectively. The cone concentric texture and perfect nanotexture are shown by high resolution transmission electron 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 for various modes of near-field microscopy on the other hand, have been tested.