A systematic study of optical and Raman spectra of peapod‐based DWNTs

We followed the preparation of double‐walled carbon nanotubes (DWNTs) from fullerene peapods by optical and Raman spectroscopy in a systematic way. 1.4 nm average diameter nanotubes were opened by oxidation in air, and filled with C 60 by sublimation. The peapods were converted to DWNTs by annealing at 1250 °C. As a reference, a control sample was also prepared, where the same sequence of treatments was applied but no C 60 was added. We monitored each preparation step from pristine nanotubes to DWNTs by Raman and wide range FIR‐UV transmission spectroscopy. Both free carrier absorption and interband transitions decrease in intensity in DWNTs, indicating that there cannot be significant charge transfer between the outer and the inner tube. Fullerene features show up in the peapod optical spectra, but the transitions of inner tubes are not observed in the DWNT spectra. In the Raman spectra of peapods, the radial breathing modes (RBMs) of the nanotubes show clear changes. Beside the shifts that were reported earlier, the linewidths of the components become smaller. The RBMs of the outer tubes are shifted back to their original position when the peapods are converted to DWNTs.