A variety of fullerene molecules are found to be fully packed in the interior space of a single-wall carbon nanotube (SWNT) and form a novel one-dimensional crystal with a regular intermolecular distance. Using electron diffraction, we have successfully measured the “lattice constants” for these crystals of various fullerenes and found that the intermolecular spacing of adjacent fullerenes in SWNTs is smaller than that of the three-dimensional bulk crystal but larger than that of polymerized crystal. It is also revealed that elongated fullerenes with a certain aspect ratio [such as ${\mathrm{C}}_{70}$ and ${\mathrm{C}}_{80}{(D}_{5d}\left)\right]$ exhibit polymorphic packing structures with different intermolecular distances due to their constrained orientations with respect to the tube axis. The packing orientations of elongated fullerenes strongly depend on the diameter of the host nanotube.

• Received 9 April 2001

DOI:https://doi.org/10.1103/PhysRevB.64.115420