Chirality-dependent Raman frequency variation of single-walled carbon nanotubes under uniaxial strain

By using a homemade setup, the length of uniaxial strained single-walled carbon nanotubes (SWNTs) was directly measured by scanning electron microscopy (SEM), and quantitative relations between uniaxial strain and Raman frequency were obtained. It was found that RBM frequency was not affected, but G-band frequency variation was diameter and chirality-dependent under uniaxial strain. The G-band frequency shift rate increased with diameter increasing and chiral angel decreasing. Also G⁺ and G^- frequency shift rates were related to chiral angle due to chirality-dependent C-C bonds elongation. A surprising finding that intermediate frequency mode (IFM) frequency upshifted with uniaxial strain increasing indicates that lattice transformation needs to be considered in phonon properties under uniaxial strain. These studies provide valuable information about geometric structure variation of SWNTs under uniaxial strain.