Structural stability and transformation of aligned C60 and C70 fullerenes in double-wall and triple-wall carbon nanotube-peapods

Clear imaging for stable phases of encapsulated fullerenes has been easily obtained only in double-wall carbon nanotubes (DWNTs) and triple-wall carbon nanotubes (TWNTs) due to the high structural stability of the host nanotubes and the encapsulated fullerenes, suggesting that investigation on DWNT- or TWNT-peapods might be a powerful approach to investigate the structures and properties of peapods. At nanotube diameters less than 1.40 nm, the stress forces between the nanotubes and the fullerenes have resulted in deformation of the encapsulated fullerenes and regular arrangement of C-70 molecules in the longitudinal orientation. At a diameter of 1.47 nm, free rotation of C-70 in different orientations is observed. For a zigzag phase of C-60 fullerenes in SWNTs, DWNTs, and TWNTs, the interaction between nanotubes and fullerenes can be expressed as attractive interactions or stress forces at different diameters of host nanotubes. Furthermore, fullerene-nanotube interactions in DWNT-peapods of different diameters are discussed by observing the material after 1200 degrees C heat treatment.