Discontinuous tangential stress in double wall carbon nanotubes.

We have examined the stability of double wall carbon nanotubes under hydrostatic pressures up to 10 GPa. The tangential optical phonon mode observed by inelastic light scattering is sensitive to the in-plane stress and splits into a contribution associated with the external and internal tube. While the pressure coefficient from the external tube is the same as in single wall carbon nanotubes, the pressure coefficient from the internal tube is found to be 45% smaller. The phonon band from the external tube broadens considerably with applied pressure in contrast with the phonon band of the internal tube which stays constant. These pressure dependent phonon shifts of the external and internal tubes and the contrasting phonon line broadening are explained by the elastic continuum shell model which takes into account both the continuous radial and discontinuous tangential stress components.

Aligned carbon nanotube films: production and optical and electronic properties.

Carbon nanotube material can now be produced in macroscopic quantities. However, the raw material has a disordered structure, which restricts investigations of both the properties and applications of the nanotubes. A method has been developed to produce thin films of aligned carbon nanotubes. The tubes can be aligned either parallel or perpendicular to the surface, as verified by scanning electron microscopy. The parallel aligned surfaces are birefringent, reflecting differences in the dielectric function along and normal to the tubes. The electrical resistivities are anisotropic as well, being smaller along the tubes than perpendicular to them, because of corresponding differences in the electronic transport properties.