The pressure dependence of the high-energy Raman modes in single-and multi-walled carbon nanotubes was measured in the range 0-10 GPa. We found the pressure coefficient to be linear in both materials but 25% smaller in MWNT. Given that the curvature effects on vibrational properties of the rolled-up graphene sheets are small, we can explain this difference simply with elasticity theory.

We investigated the hydrostatic and shear strain components introduced in the graphite hexagons by applying hydrostatic pressure to single-walled carbon nanotubes. The vibrational modes are expected to show different pressure derivatives depending on the polarization of the eigenvector with respect to the nanotube axis, but independent of chirality. A comparison with tight-binding calculations allows us to estimate the Grüneisen parameter ͑1.24͒ and the shear phonon deformation potentials ͑0.41͒; they compare favorably with experimental results on nanotubes.

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Using Raman spectroscopy we determined the van-der-Waals component of the low-frequency vibration in ropes of single-walled nanotubes at 171 cm À1 . While Raman peaks in this frequency range are commonly believed to correspond to the pure radial breathing mode of a single tube, our pressure and temperature-dependent measurements show that van-der-Waals contribution of the peak observed at 514.5 nm excitation is necessary to explain its large pressure coefficient of 9.7 cm À1 /GPa. Our results are consistent with the small elastic modulus predicted for nanotube ropes.

Resonance excitation profiles of the high-frequency peaks in the Raman spectra of single-walled carbon nanotubes normalized to the scattering intensity of CaF 2 are presented. We find separate resonances of metallic and semiconducting tubes throughout the visible and the near-IR excitation range. The resonance shift of samples with different mean diameters confirm the inverse proportionality of the resonant transition energy to the tube diameter. Smaller diameter tubes are found to have sharper resonances than larger tubes due to a 1/d 2 dependence of the Raman cross section.