Observation of ordered phases of fullerenes in carbon nanotubes

We have assembled molecular arrays of C-60 inside double-walled carbon nanotubes (DWNTs) with internal diameters of 11-26 Angstrom and directly observed the existence of different crystalline phases of C-60 previously predicted theoretically. The structure of the encapsulated C-60 crystal is defined by the internal diameter of the DWNT, as the molecules adjust their packing arrangement in order to maximize van der Waals interactions. We have also shown that fullerenes in C-60@DWNT interact with the outer layer of DWNTs, as demonstrated by the efficient filling of DWNTs with internal diameters of less than 12 Angstrom.