Vertically aligned double- and single-walled carbon nanotubes (DWNTs and SWNTs) were synthesized on a substrate at 590 °C by hot-filament chemical vapor deposition. An optimized combination of iron and aluminum layers as the catalyst resulted in iron particles ranging from 1-5 nm floating in an aluminum matrix after annealing. Selective synthesis of DWNTs and SWNTs from such particles was achieved by adjusting the dilution ratio of acetylene that was used as the source gas. The yield of DWNTs among all CNTs was as high as 81%, while that of SWNTs was almost 100%. The diameter distribution of DWNTs was narrow, with a standard deviation of about 12%.
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