Raman spectral probing of electronic transition energy e_ii variation of individual SWNTs under torsional strain

We present herein a rational approach to probe the torsional strain-induced electronic transition energy E_ii variation of individual SWNTs by resonant Raman spectroscopy (RRS). When a SWNT was manipulated by AFM tip through a path perpendicular to SWNT axis, both torsional and uniaxial strain would be introduced in SWNTs. Under the torsional strain, resonant Raman spectral mapping along a SWNT detected an M-shaped frequency (ω_RBM) and W-shaped intensity (I_S) variation of radial breathing mode (RBM) spectra, which were induced by the elastic retraction of the nanotubes in combination with the friction after the tip has been removed. The electronic transition energy E_ii variation along SWNTs by torsional strain follows a family pattern based on q = (n - m) mod 3: for semiconducting SWNTs, E₃₃^S increases for q = +1, E₃₃^S decreases and E₂₂^S increases for q = -1, and for metallic SWNTs, E₁₁^M always increases.