Resonant Raman spectroscopy of individual metallic and semiconducting single-wall carbon nanotubes under uniaxial strain

Abstract

Uniaxial strain is induced by pushing single-wall carbon nanotubes ͑SWNTs͒ with an atomic force microscope tip. The vibrational and electronic energies of nanotubes are found to be very sensitive to strain. For both metallic and semiconducting SWNTs under strain, the D, G, and GЈ band Raman modes are downshifted by up to 27, 15, and 40 cm −1 , respectively. The relative strain-induced shifts of the D, G, and GЈ bands vary significantly from nanotube to nanotube, implying that there is a strong chirality dependence of the relative shifts. Semiconducting SWNTs remain strongly resonant under these large deformations, while metallic SWNTs appear to move in and out of resonance with strain, indicating a strain-induced shifting of the electronic subbands. Tight-binding calculations of the electronic band structure of semiconducting and metallic nanotubes under uniaxial strain predict significant shifting of the subband energies, leading to strain-induced changes in the Raman intensity. These theoretical predictions are consistent with what we observe experimentally for metallic nanotubes, but not for semiconducting nanotubes.

Monitoring a Micromechanical Process in Macroscale Carbon Nanotube Films and Fibers

“…As shown in Figure 2d, at the low-strain stage, macroscale strain of the specimen mainly arises from the uniform deformation of the meshes rather than axial extension of the bundles. According to Corning's report, the average downshift rate of the G 0 band for strained individual SWNTs is 37.5 cm À1 per 1% strain, [16] which is 56 times and 21 times higher than that of our films and fibers, respectively. Such small downshift rates in our case imply that SWNTs' axial extensions merely contribute several percent to the total macroscale strain, which results in the remarkable drop of the macroarchitecture moduli compared with that of the individual CNTs.…”

“…[13,14] Moreover, since Raman scattering is sensitive to the inter-atomic distance, when CNTs are mechanically strained, there is a linear relationship between the Raman peaks' shift and local strain. [15,16] Wagner's group has demonstrated a successful case of utilizing CNTs as stress sensors in composite materials. [17] In this report, we introduce Raman measurements to strained macroscale SWNT films and fibers.…”

Tip-enhanced nano-Raman analytical imaging of locally induced strain distribution in carbon nanotubes

“…The dragging method described above introduces local strains in the nanotube by rolling (torsional strain), stretching (tensile strain) or a combination of both [34][35][36] . TERS imaging, which involves Raman spectroscopy, is the best approach to visualize and analyse these local strains [37][38][39][40] . Raman scattering can even distinguish between torsional and tensile strains in CNTs because the G þ -mode around 1,590 cm À 1 in Raman scattering shifts Raman shift (cm -1 )…”

“…This process often develops local strain in the nanotubes. Although AFM-induced strains have been observed via confocal Raman spectroscopy with diffractionlimited spatial resolution [37][38][39][40] , it has not been easy to investigate the localized nature of such strains that can be confined within nanoscale region, which can significantly affect the device performance.…”

Uniaxial Strain on Graphene: Raman Spectroscopy Study and Band-Gap Opening

“…16Ϫ18 The high strain sensitivity of graphene successfully demonstrates its potential as an ultrasensitive strain senor as has been proved using the CNTs. 16 The linear dependence of Raman bands with strain is expected according to the phonon deformation potentials. The frequency shift of the Raman band is related to the uniaxial strain and the shear strain. )…”