Low-temperature growth of vertically aligned single-walled carbon nanotubes by radical CVD

Very dense and vertically aligned single-walled carbon nanotubes (SWNTs) were synthesized using a radical CVD apparatus at a low temperature of 600 degrees C. A high density of catalytic particles, which is necessary for the growth of vertically aligned SWNTs, was prepared by heat treatment of a sandwich-like catalyst structure of Al2O3/Fe/Al2O3. In our CVD apparatus, a sphere-shaped microwave plasma ball was fixed at the antenna in the chamber and was 50 mm away from the substrate, which indicates that ions cannot contribute to the growth of SWNTs. The radical CVD system produced a very long catalyst lifetime of over 30 h, because catalysts were not damaged and etched by ions. Using the catalysts with the long lifetime, lengths of SWNTs increased to millimeter order. Root growth mode of SWNTs was clarified by marker growth, which synthesized two vertically aligned SWNT layers on a substrate at different growth times.