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) Comparison of the activation process of the D-band between conventional and plasmonic excitation. (a) Conventional resonance Raman scattering (RRS) process. (b) Gradient-field Raman (GFR) process.