We investigate the limits of high energy transport in multiwalled carbon nanotubes (MWNTs). In contrast to metal wires, MWNTs do not fail in the continuous, accelerating manner typical of electromigration. Instead, they fail via a series of sharp, equally sized current steps. We assign these steps to the sequential destruction of individual nanotube shells, consistent with the MWNT's concentric-shell geometry. Furthermore, the initiation of this failure is very sensitive to air exposure. In air failure is initiated by oxidation at a particular power, whereas in vacuum MWNTs can withstand much higher power densities and reach their full current carrying capacities.

• Received 28 August 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.3128