Specific features of tangential modes in Raman scattering spectra of semiconducting single-walled carbon nanotubes with a large diameter

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The lattice dynamics and optical properties of individual semiconducting single-walled carbon nanotubes with diameters of greater than 2.0 nm have been investigated using resonant Raman spectroscopy over a wide range of laser excitation wavelengths. Individual suspended semiconducting single-walled carbon nanotubes have been synthesized by the chemical vapor deposition method. The chirality indices (n, m) of the carbon nanotubes have been determined using the electron diffraction method. The dependences of the ratios of absolute intensities of the tangential transverse optical and tangential longitudinal optical modes on the laser excitation energy and on structural parameters (diameter and chiral angle) of the nanotube have been established. The observed dependences are inconsistent with the spectral data obtained previously for structurally identified individual semiconducting single-walled carbon nanotubes with diameters of less than 1.1 nm.