Effect of fullerene encapsulation on radial vibrational breathing-mode frequencies of single-wall carbon nanotubes.

We investigate the effects of C60 fullerene encapsulation on the radial breathing mode (RBM) of semiconducting single-wall carbon nanotubes (SWCNTs) under tunable laser excitations. The changes in the RBM frequencies after C60 insertions show characteristic behavior; higher frequency shifts are observed in the case of smaller diameter tubes (dt<or =1.32 nm) and lower frequency shifts, in the case of larger diameter tubes (dt>or =1.32 nm). The observed frequency shifts are satisfactorily explained by the diameter-dependent interaction between the encapsulated C60 and the host SWCNTs.