Carbon-nanotube formation directly on a substrate by an electron beam

Polyyne-containing carbons are transformed to multi-wall carbon nanotubes (CNTs) in a transmission electron microscope. This technique has an advantage to observe the CNT growth in an in-situ way, and the CNTs have been found to grow in a two-step process: quick formation (a few seconds) of rod-like carbons, and slow formation (1 min) of the hollows inside the rods accompanied by graphitization of the walls. The technique has a possibility to be applied to fabricate CNT devices. Thus the growth conditions (heating temperature and its duration) were investigated and are discussed in this paper. The heating duration affects the number of graphene layers of the wall, while the temperature does not affect the length, the diameter, and the number of graphene layers. The longer heating duration, which corresponds to less supply of the precursor due to its evaporation in vacuum, leads to thinner walls and more round-shaped caps. This finding corresponds to the formation mechanism, i.e. growth from the bottom in a solid phase, which has been assumed for this technique.