Temperature dependent Raman spectra of carbon nanobuds

Carbon nanobuds (CNBs) represent an emerging nanostructure, in which fullerene molecules are covalently bonded to the outer surface of single-walled carbon nanotubes (SWNTs). The Raman spectra of CNBs were systematically investigated and compared to those of SWNTs. The spectra were recorded using a 514 nm laser and evaluating the temperature-dependent Raman frequency shift in CNBs in the range 27−475 °C. The temperature coefficient of the G-mode frequency of the CNBs was much larger than that of the SWNTs. Consequently, the CNBs have lower thermal stability, which is attributed to the fact that the fullerenes are covalently bonded to the sidewall of SWNTs. At the same time, we observed that the radical breathing modes (RBMs) of CNBs downshift ∼2−6 cm⁻¹ compared to the RBMs of SWNTs, and this shift can be attributed to the smaller van der Waals (VDWs) interactions between the CNBs. Using a 750 nm laser, a broad G⁻ band, which is an intrinsic character of metallic properties, was clearly observed. This characteristic feature provides evidence that the nanobuds of some nanotubes remain metallic.