Carbon micro- and nanotubes synthesized by PE-CVD technique: Tube structure and catalytic particles crystallography

Abstract

The structure of carbon micro- and nanotubes synthesized by the plasma-enhanced (PE) PE-CVD technique has been investigated by SEM, TEM, SAED and HRTEM. It is shown that tubes are formed by structurally defective versions of conical graphene layers. There are three types of tubes; (1) with a straight inner channel, (2) with a straight channel but helical walls, (3) with a helical channel. In some cases the channel is located very close to the outer surface of the tubes and rotational symmetry of conical layers is violated. The helicity can be explained by anisotropy of the catalytic properties at the nickel–carbon interface. Catalytic particles (CPs) are Ni single crystals, and facets promoting carbon are {1 0 0} and {1 1 0}. It is shown that carbon emitting CP facets are vicinal or non-singular and these govern the structure of the tubes. EELS and chemical mapping revealed that Ni is captured by a growing tube.