Raman Intensities of Totally Symmetrical Modes of Homogeneously Deformed Single-Walled Carbon Nanotubes

Abstract

Raman excitation profiles for 55 homogeneously deformed single-walled carbon nanotubes with diameters from 0.7 to 1.2 nm are calculated and systematically analyzed. Torsion and uniaxial strain produce a number of interesting observable effects, important in designing electromechanical devices. The deformations shift phonon energies. The torsion alone causes mixing of high energy modes, while the uniaxial compression generates interchange of their vibrating directions. It is found that electronic transition energies depend almost linearly on deformation; for some tubes, they cover the entire visible spectrum, making them perfectly tunable light absorbers. On the other hand, this shift causes a number of interference effects. The type of interference and its influence on the excitation profiles is completely determined by electron–phonon coupling matrix elements. Collapse of Raman intensity in resonant scattering experiments is explained either by destructive interference or by moving away from the resonant window. Finally, the deformation causes increase of the lower high energy mode resonant intensity, which should further produce the appreciable change in the G mode profile.