G-band variation of individual single-walled carbon nanotubes under torsional strain

Strain can effectively modulate the structure and properties of single-walled carbon nanotubes (SWNTs), and hence is an important aspect in their researches and applications. In this article, the effect of torsional strain on the G-band modes of individual SWNTs is reported. When torsional strain is induced by atomic force microscopy (AFM) manipulation, G-band of SWNTs varies significantly. Following G-band modes (2A_1g, 2E_1g, and 2E_2g) assignment by polarized resonant Raman spectroscopy, it is found that modes with different symmetries respond quite differently to torsional strain. On the basis of the analyses of eight individual SWNTs, we find that the variation of G-band is sensitive to the diameter and chirality of SWNTs. Finally, the nonresonant Raman spectra of chiral (12, 4) SWNTs are calculated using the ab initio calculations and the empirical bond polarizability model, which further confirms that there are some relations between mode symmetries and the effect of torsional strain on Raman spectra.