Optical properties of carbon nanotubes under axial strain.

A review is given of Raman spectroscopy of carbon nanotubes under axial strain. Carbon nanotubes possess a high Young's modulus (1 TPa) and breaking strains of 5-15%. Resonance Raman spectroscopy reveals changes in the electronic energies and lattice structure of nanotubes under applied strain. Studies performed on composite materials, where nanotubes have been added to increase the material's strength, are reviewed. Measurements of individual nanotubes under strain are also presented. Emphasis is given to the important new physics revealed by observing the strain-induced changes in the Raman spectra of individual nanotubes. A brief review of theoretical calculations performed on nanotubes under strain is also presented. The implications for using carbon nanotubes as a high strength material and as a strain sensitive material are indicated.