Weak Response of Metallic Single-Walled Carbon Nanotubes to C60 Encapsulation Studied by Resonance Raman Spectroscopy

Abstract

Metallic single-walled carbon nanotubes (SWCNTs) have been regarded as unique quasi-1D metallic systems. Their basic properties significantly differ from those of their semiconducting counterparts even though their chemical compositions and sizes are nearly identical to each other. In this study, we investigate the effects of C60 fullerene encapsulation on the phonon and electronic properties of metallic SWCNTs by resonance Raman spectroscopy. The changes in the radial breathing mode frequencies and the optical transition energies after C60 insertions show characteristic tube diameter dependences, as in the case of the corresponding semiconducting SWCNTs. Although the observed behaviors can be attributed to the intermolecular interaction between SWCNTs and the encapsulated C60, similar to the corresponding semiconducting SWCNTs, the strength of the interaction is measurably weaker than that of semiconducting SWCNTs. The present findings provide important insight into the essential differences in the basic nature of metallic and semiconducting SWCNTs.