Effect of different metal deposition methods on the growth behaviors of carbon nanotubes

It is generally known that the catalyst particles promote tip or base growth of carbon nanotubes depending on the contact force between the catalyst particles and the substrate. We have investigated the correlation between the growth modes of vertically aligned carbon nanotubes (CNTs) and the adhesion of Ni catalyst particles to the Si substrates. It is shown that Ni films (10 nm thick) deposited by pulsed laser deposition (PLD) and electron beam evaporation are broken up into nanoparticles and/or islands when pretreated in NH3 gas ambient at 850 °C for 20 min. It is found that CNT growth on the PLD substrate proceeds by base growth mode, whereas CNT growth on the electron-beam evaporated substrate is operated by tip growth mode. The different CNT growth behaviors are explained in terms of the difference of the adhesion between the Ni catalyst particles and the substrate due to the different kinetic energy of depositing Ni particles.