Abnormal Raman Intensity of Single-Walled Carbon Nanotubes Grown on Silica Spheres

Resonant Raman scattering experiments are carried on single-walled carbon nanotubes (SWCNTs) suspended between silica spheres. Weak uniaxial strain is introduced into these tubes during the chemical vapor deposition growth process. The metallic nanotubes exhibit different behavior from their semiconducting counterparts under the uniaxial strain. The G band shows no change in position and shape for metallic nanotubes, while for semiconducting nanotubes the G mode changes in profile but does not change in position. The radial breathing mode (RBM) maintains its position under the uniaxial strain for all the tubes. Most of the Raman spectra show an intense RBM, even for large diameter (∼2 nm) semiconducting SWCNTs and armchair SWCNTs. The large RBM/G band intensity ratio is ascribed to the much longer lifetime of the excited electronic states in the resonant process.