Synthesis and Raman scattering study of double-walled carbon nanotube peapods

Double-walled carbon nanotubes (DWNTs) encapsulating C60 fullerenes were successfully synthesized by gas phase diffusion method. The obtained peapods were examined using high-resolution transmission electron microscopy (HRTEM). The HRTEM images indicate that the ordered packing phases of fullerene molecules inside are sensitively related to the inner-tube radius of DWNTs. Also, Raman measurements were carried out for the first time to characterize DWNTs peapods. There are obvious differences between the Raman spectrum of DWNTs peapods and that of SWNTs peapods. The intensities of resonances from C60 in the former are much stronger than those in the latter. In addition, changes of tangential mode (TM) and radial breathing mode (RBM) of DWNTs after C60 doping were observed. The possible reasons are discussed in the text.