Detection of invisible phonon modes in individual defect-free carbon nanotubes by gradient-field Raman scattering

Yang Feng^{1, 3, 4}, Ji Yinglu^{2, ‡}, Zhang Xiao^{1, 4}, Fan Qingxia^{1, 4}, Zhang Nan^{1, 4}, Gu Xiaogang^{1, 3, 4}, Xiao Zhuojian^{1, 3, 4}, Zhang Qiang^{1, 4}, Wang Yanchun^{1, 3}, Wu Xiaochun^{2, 4}, Li Junjie¹, Zhou Weiya^{1, 3, 4, †}

(color online) (a) SEM image of the SWNT after the Au NP cluster was removed by water. The scale bar is 500 nm. (b) The corresponding Raman spectra of the SWNT shown in (a).