SWNT growth on Al_2O_x/Co/Al_2O_x multilayer catalyst using alcohol gas source method in high vacuum

摘要

Al_2O_x/Co/Al_2O_x multilayer catalysts were employed to grow single-walled carbon nanotubes (SWNTs) by an alcohol gas source method in a high vacuum. Compared to a Co/Al_2O_x bilayer catalyst, the SWNT yield was drastically enhanced for growth at 700℃ by optimizing the thickness of the A1_2O_x top layer, and vertically aligned SWNTs could be grown even at a low ethanol pressure of 1.0×10~(-1) Pa. At a growth temperature of 400 °C, the yield enhancement effect decreased and was observed only for a 0.2 nm Al thickness of the A1_2O_x top layer. The distribution of SWNT diameters at 400℃ estimated from the Raman spectra showed that there is little difference between the Co/Al_2O_x bilayer and the Al_2O_x/Co/Al_2O_x multilayer catalysts, in marked contrast to the distribution at 700℃. These results suggest that surface migration of Co atoms is suppressed at 400℃ and the size of the Co catalyst particles is kept small even at the growth temperature, which leads to small enhancement effect of the A1_2O_x top layers.