Carbon nanotube growth from ion-implanted catalyst by chemical vapor deposition

Abstract

We present experimental evidence that iron ions implanted into silicon/silicon dioxide substrates form nanoscale islands during subsequent annealing, which act as catalyst for nanotube chemical vapor deposition (CVD) growth. We have implanted Fe + ions into thermally grown SiO 2 layers on silicon substrates with an energy of 60 keV and a dose of 10 15 cm -2 . Using this implanted catalyst, we have then grown carbon nanotubes by CVD at 900 o C with methane as the precursor gas. We have characterized the catalyst islands and the grown carbon nanotubes by Atomic Force Microscopy (AFM) and Raman spectroscopy. The diameters of carbon nanotubes we have grown from ion implanted catalyst in this work are much smaller than those reported previously. The presence of small diameter nanotubes implies single-walled nanotube (SWNT) growth. The height distribution of the catalyst islands correlates very well with the diameter distribution of nanotubes. This is consistent with previous work which has found evidence that nanotube diameter depends strongly on the size of the catalyst particles.Since ion-implantation can be easily masked by lithography, this technique of nucleating nanotube growth opens up the possibility of controlling the origin of nanotubes at the nanometer scale over high aspect ratio topography. This technique also has the advantage that it can easily be integrated with silicon processing, and scaled to larger substrates.