New probes based on carbon nano-cones for scanning probe microscopies.

All-graphenic carbon morphologies grown on individual carbon nanotubes (CNTs) consisting of short-fiber segments bearing sharp micro-/nano-cones at both ends were mounted as new probes for scanning probe microscopies (SPM). Three mounting procedures were tested, two based on focused ion and/or electron beam processes operated in scanning electron microscopes, and another based on an irradiation-free procedure under an optical microscope. The benefits and drawbacks of all the methods are described in details. The extent to which the structural integrity of the carbon material of the cones was affected by each of the mounting processes was also investigated using Raman spectroscopy and high-resolution transmission electron microscopy. The carbon cones were found to be sensitive to both ion and electron irradiation to an unusual extent with respect to structurally-close nano-objects such as multi-wall CNTs. This was assumed to be due to the occurrence of a large number of free graphene-edges at the cone surface. The suitability of such carbon cones as SPM probes is demonstrated, the characteristics of which make them potentially superior to Si-, diamond-, or CNT-probes.

Texture, Nanotexture, and Structure of Carbon Nanotube-Supported Carbon Cones.

Graphene-based carbon micro-/nano-cones were prepared by depositing pyrolytic carbon onto individual carbon nanotubes as supports using a specific chemical vapor deposition process. They were investigated by means of high-resolution scanning electron microscopy, low-voltage aberration-corrected transmission electron microscopy, Raman spectroscopy, and molecular dynamics modeling. While the graphenes were confirmed to be perfect, the cone texture was determined to be preferably scroll-like, with the scroll turns being parallel to the cone axis. Correspondingly, many of the concentrically displayed graphenes (actually scroll turns) exhibit the same helicity vector. When radii of curvature are large enough, this could allow for coherent stacking to locally take place in spite of the lattice shift induced by the curvature. A particular care was taken on investigating the cone apexes, in which a specific type of graphene termination was observed, here designated as the "zip" defect. Calculations determined a plausible stable structure that such a defect type may correspond to. This defect was found to generate a very low Raman ID/ID' band ratio (1.5), for which physical reasons are proposed. Combining our results and that of the literature allowed proposing an identification chart for a variety of defects able to affect the graphene lattice or edges.