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.