The insertion of C60 into multi-walled carbon nanotubes was studied. The commercial C60-nanotubes were added to the opened multi-walled carbon nanotubes in a weight ratio of 1 to 7. The mixture was afterwards vibrated in toluene for 12 min and air-dried. It was found that the diffusion of C60 took place through the open tube ends, and when the diameter of the innermost graphite tube was about 2nm, the fullerenes tended to form zig-zag chains.

Insertion of C60 into Multi-Wall Carbon Nanotubes - a Synthesis of C60@MWCNT. Fröhlich, T., Scharff, P., Schliefke, W., Romanus, H., Gupta, V., Siegmund, C., Ambacher, O., Spiess, L.: Carbon, 2004, 42[12-13], 2759-62