Mechanism of the effect of NiCo, Ni and Co catalysts on the yield of single-wall carbon nanotubes formed by pulsed Nd:YAG laser ablation

We revealed that the yield of SWNTs formed by Nd:YAG laser ablation depends on the target composition with yields following the order CxNiyCoy > CxNiy much greater than CxCoz. The SWNT bundles in the web formed when using the CxNiyCoy target (web-CxNiyCoy) is thicker and longer than those in the web-CxNiy. The diameters of the SWNTs in the web-CxNiyCoy were larger and more uniform than those of the SWNTs in the web-CxNiy. The NiCo particles in the web-CxNiyCoy and the Ni particles in the web-CxNiy were nanometer sized and were embedded in the amorphous carbon flakes that were dispersed throughout the weblike deposits. Filmlike deposits were formed when using the CxCoz targets, and nanometer-sized Co particles in these deposits were localized within sub-millimeter-sized areas. Examination of the target surfaces revealed that Ni emits from the CxNiy target more efficiently than NiCo from the CxNiyCoy target or Co from the CxCoz target during the laser ablation. On the basis of these results, we provide an explanation of how the yield and structure of SWNTs formed by laser ablation depend on the species of the metal catalysts.