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 degrees 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 x 10(-1) Pa. At a growth temperature of 400 degrees C, the yield enhancement effect decreased and was observed only for a 0.2 nm Al thickness of the Al2Ox top layer. The distribution of SWNT diameters at 400 degrees 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 degrees C. These results suggest that surface migration of Co atoms is suppressed at 400 degrees 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. (C) 2010 Elsevier B.V. All rights reserved.