Growth mechanism of vertically aligned carbon nanotubes on silicon substrates

We have synthesized vertically aligned carbon nanotubes by thermal chemical vapor deposition using C2H2 gas on a large area of transition metal-coated Si substrates. It is observed that control of nucleation sites of transition metals deposited on Si substrates by a dipping in a HF solution and/or NH3 pretreatment is a crucial step for the growth of vertically aligned carbon nanotubes prior to the reaction of C2H2 gas. We show that the transition metals play as nucleation seeds and lead to further cap growth by forming a metal cap at the end of nanotubes.