A simple route to short cup-stacked carbon nanotubes by sonication

A simple but effective way of producing short cup-stacked carbon nanotubes with high quality is demonstrated using sonication in an ethanol/distilled water mixture. The substantial removal of amorphous carbon deposited on the truncated conical layer-stacked nanotubes by controlled air oxidation was a critical precondition to cut the nanotubes without substantial structural degradation. The short nanotubes (below 1 μm) prepared by a sonication-generated shear force exhibited a narrow length distribution (median length = 0.2 μm) and chemically active edges in the outer surface, thereby resulting in high dispersibility in an aqueous solution.