Mechanism of selective growth of carbon nanotubes on SiO2/Si patterns

During the chemical vapor deposition of multiwalled carbon nanotubes using the vapor phase delivery of a metal-organic (ferrocene) catalyst precursor, a strong selectivity for growth on patterned SiO2/Si substrates has been observed. A mechanism for this selective growth is described here. Delivered metal particles (Fe) on Si and SiO2 regions were investigated using several high-resolution characterization techniques. Active iron catalyst (gamma iron) particles were formed on the silicon oxide surface resulting in the formation of highly aligned nanotubes on this substrate. However, in the Si regions, stable FeSi2 and Fe2SiO4 particles were formed due to chemical reactions between silicon surface and Fe particles at high temperature leading to an inhibition of nanotube growth in the Si regions.