Light scattering of double wall carbon nanotubes under hydrostatic pressure: pressure effects on the internal and external tubes

We report high-pressure Raman light scattering studies up to 10 GPa on double walled carbon nanotubes using two pressure transmitting media. In alcohol, a clear splitting of the G band is observed up to 10 GPa. This splitting is evidence for both discontinuous tangential stress and continuous radial stress. A structural distortion seems to be present at 3 GPa, revealed by a spectroscopic signature at 1480 cm -1 . With argon as the pressure transmitting medium, the nanotubes bundles show a transition at 6 GPa which corresponds to a collapse to a flattened structure and removes the splitting. The comparison of the pressure coefficients before the transition for the two pressure transmitting media shows that the ratio of the two coefficients associated with internal and external tubes, is the same but the absolute values are different.