Laboratoire de Physique Théorique
Toulouse - UMR 5152

Carbon Nanotubes (CNTs) have been reported to be used as key elements in nanoelectromechanical systems such as nanorelays, nanoswitches, nanotweezers and feedback device which are designed for memory, sensing or actuation uses. Understanding of their electromechanical properties is one of the important issues for their promising applications. We have computed the deformations of semiconducting [1] and metallic [2] CNTs induced by uniform electrostatic fields, by minimizing total potential energy calculated using a monopoledipole- interaction model combined with an empirical many-body potential (AIREBO). The effects of field strength, field direction tube geometries and defects on the electrostatic deformation are investigated. For metallic CNTs, they are much easier to be deflected than semiconducting ones. The multi-walled metallic CNTs are found to be much harder to be bent in electric fields than single-walled CNTs. Furthermore, we find that the electrostrictive deformation of CNTs is proportional to the square of field strength. We also present another detailed study on the static enhancement effects of electric charges in CNTs, by using theoretically an atomic charge-dipole model and experimentally electrostatic force microscopy. We demonstrate that nanotubes exhibit surprisingly weak charge enhancement at the tube ends in specified experimental conditions. Our studies reveal that the charge enhancement ratio decreases with the tube length and increases with the tube radius. Quantitative agreement is obtained between theory and experiment [3].

[1] Z. Wang, M. Devel, R. Langlet, and B. Dulmet, Phys. Rev. B 75, 205414 (2007). [2] Z. Wang, M. Devel, Phys. Rev. B 76, 195434 (2007). [3] Z. Wang, M Zdrojek, T. Melin and M. Devel, submitted.