The growth of single-walled carbon nanotubes on a silica substrate without using a metal catalyst

Single-walled carbon nanotubes (SWCNTs) have been directly grown on a SiO₂ substrate using the chemical vapor deposition (CVD) of ethanol without a catalyst. Care was taken to exclude the possibility that the SWCNT growth was induced by conventional metal catalysts such as Fe, Co and Ni resulting from the contamination. Pretreatment of the SiO₂ at 950 °C or a higher temperature in H₂ before CVD was critical for the synthesis of SWCNTs. After CVD process, nano-scale carbon particles were produced besides SWCNTs. Based on these results, we propose that the annealing of SiO₂ substrates in H₂ at high temperature generates defects on their surfaces, and these defects provide nucleation sites for the formation of carbon nanoparticles and assist the formation of carbon nanocaps, thus leading to the SWCNT growth.