Metal-Catalyst-Free Growth of Single-Walled Carbon Nanotubes on Substrates

In this communication, we have demonstrated that SiO2 nanoparticles can be generated by simply scratching the quartz or silicon wafer with a SiO2 layer and confirmed it to be active for the growth of SWNTs for the first time. Furthermore, the SWNTs from SiO2 has a much narrower size distribution. This may open a way to control the diameter of the SWNTs. More importantly, our work has found a series of oxides including Al2O3, TiO2, and rare earth oxides to be active for SWNT growth as well. These findings not only provide an alternative new type of catalysts for the growth of SWNTs but also give more insight into the role of the catalysts and a deeper understanding of the growth mechanism of SWNTs. The effective catalysts and catalytic activity for SWNT growth seem to be more size-dependent than the catalysts. Long oriented SWNTs generated from these catalysts enable us to rule out the relationship between the catalysts and the structures of the SWNTs. Thus controlled growth of SWNTs including the diameter and chirality is expected to be eventually realized.