Charge-induced anisotropic distortions of semiconducting and metallic carbon nanotubes

To accommodate extra electrons or holes injected into a single-wall carbon nanotube, carbon-carbon bonds adjust their lengths. Resulting changes in carbon-nanotube length as a function of charge injection provide the basis for electromechanical actuators. We show that a key mechanism at low injection levels, modulation of electron kinetic energy, provides nanotube deformations that are both anisotropic and strongly dependent on nanotube structure. Nanotubes can exhibit both expansion and contraction, as well as nonmonotonic size changes. The magnitude of the actuation response of semiconducting carbon nanotubes may be substantially larger than that of graphite.