Measuring the Uniaxial Strain of Individual Single-Wall Carbon Nanotubes: Resonance Raman Spectra of Atomic-Force-Microscope Modified Single-Wall Nanotubes

Raman spectroscopy is used to measure the strain in individual single-wall carbon nanotubes, strained by manipulation with an atomic-force-microscope tip. Under strains varying from 0.06%–1.65%, the in-plane vibrational mode frequencies are lowered by as much as 1.5% ($40{\mathrm{c}\mathrm{m}}^{-1}$), while the radial breathing mode (RBM) remains unchanged. The RBM Stokes/anti-Stokes intensity ratio remains unchanged under strain. The elasticity of these strain deformations is demonstrated as the down-shifted Raman modes resume their prestrain frequencies after a nanotube is broken under excessive strain.

Figure 1

(a) AFM image of a SWNT held fixed at the ends by metal electrodes, after the SWNT was strained by 0.53% with an AFM tip. The white circles indicate the size and position of the $\sim 1\mu \mathrm{m}$ laser spot when Raman spectra were taken. (b) RBM and $D$ band and (c) $G$ and $G^{\prime }$ band Raman spectra for the semiconducting SWNT in (a) before and after inducing 0.53% strain. The “left” $G$ band spectrum, taken at the position indicated by the left white circle in (a), indicates that the strain extends along the length of the SWNT. Data taken one week after the strain was introduced shows relaxation of the Raman peaks back toward their original positions.

Figure 2

AFM images of a SWNT that was strained by 1.65% with an AFM tip (a) before and (b) after being broken by the AFM tip. (c) $G$ band and (d) $D$ and $G^{\prime }$ band Raman spectra for the SWNT shown in (a) before and after inducing 1.65% strain, and after breaking the nanotube with the AFM tip. Data taken after the SWNT was broken shows relaxation of the Raman peaks back to their original positions.