High-field electrical transport and breakdown in bundles of single-wall carbon nanotubes

We investigate high-field transport in bundles of single-wall carbon nanotubes (SWNTs) with multiple contacts. The bundles carry currents in excess of $250\mu \mathrm{A}$ (a current density of ${10}^9\mathrm{A}/{\mathrm{cm}}^2)$ before saturation and electrical breakdown, indicating that conduction is predominantly by nanotubes on the surface of the bundle which are directly contacted by electrodes. Using a four-probe configuration, we measure the contact resistance and show that it is nearly constant as the bias voltage varies. This strongly supports the notion that electron-phonon scattering, and not a contact effect, causes current saturation at high-field. Electrical breakdown proceeds by sequential destruction of individual metallic nanotubes on the bundle surface, with steplike current drops of about $12\mu \mathrm{A}.$ At very high bias, the current-carrying capacity of the bundle increases due to field-enhanced coupling between nanotubes in the bundle.