Abstract
Al2Ox/Co/Al2Ox 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/Al2Ox bilayer catalyst, the SWNT yield was drastically enhanced for growth at 700°C by optimizing the thickness of the Al2Ox top layer, and vertically aligned SWNTs could be grown even at a low ethanol pressure of 1.0×10−1Pa. At a growth temperature of 400°C, the yield enhancement effect decreased and was observed only for a 0.2nm Al thickness of the Al2Ox top layer. The distribution of SWNT diameters at 400°C estimated from the Raman spectra showed that there is little difference between the Co/Al2Ox bilayer and the Al2Ox/Co/Al2Ox multilayer catalysts, in marked contrast to the distribution at 700°C. These results suggest that surface migration of Co atoms is suppressed at 400°C and the size of the Co catalyst particles is kept small even at the growth temperature, which leads to small enhancement effect of the Al2Ox top layers.
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