Electromechanical instabilities of suspended carbon nanotubes-multi mode excitations

Artikel i vetenskaplig tidskrift, 2007

We investigate theoretically the occurrence of shuttle-like electromechanical instabilities in systems where charge transfer processes interact with several mechanical degrees of freedom simultaneously. In particular we consider the excitation of the multiple bending modes of a suspended carbon nanotube (CNT) due to the injection of current from the tip of a scanning tunnelling microscope (STM) into the suspended part of the tube. With respect to the shuttle instability, we show that the different bending modes can be treated independently in the limit of weak electromechanical coupling. As a result one or more modes—depending on the strength of the tunnel coupling between the CNT and the STM-tip—can be unstable.We find that it is possible to selectively excite a specific mode by tuning the distance between the STM-tip and the CNT. Furthermore, we have investigated the stable (limit cycle) regime that develops as a result of the shuttle instability when only one bending mode is unstable.