Fullerene peapods and double-wall nanotubes: Structures and optical properties

High‐yield fullerene‐peapods were synthesized by using diameter selected nanotubes. Filling factors of C60 and C70 were estimated from X‐ray diffraction analysis. The best filling is 100 % for C70‐peapods. Peapods were transformed to double‐wall nanotubes simply by heating in vacuum. Drastic spectral change in radial breathing modes and tangential modes were observed with an intensity drop in the conversion process. Limited number of radial breathing mode peaks originated from inner nanotubes was observed in resonance Raman spectra, which is consistent with a tight binding calculation of electronic band structure for thin nanotubes.