Synthesis of vertically aligned single- and double-walled carbon nanotubes without etching agents

The number of graphene shells on carbon nanotubes (CNTs) can be rationally controlled to yield high-density, vertically aligned single- and double-walled CNTs. This was obtained by thermal chemical vapor deposition at 700 degrees C without the use of etching agents such as water, oxygen, or plasma. The key factors for this success are controlled dissociative adsorption of acetylene (C2H2) molecules and subnanometer thickness control of the Al/Fe/Mo trilayer films. We propose that an Al concave meniscus confines the actual growth surface areas of Fe/Mo catalytic nanoparticles and enables the control of the number of graphene shells on CNTs.