Shuttle instability in self-assembled Coulomb blockade nanostructures

We study a simple model of a self-assembled, room temperature Coulomb-block ade nanostructure containing a metallic nanocrystal or grain connected by s oft molecular links to two metallic electrodes. Self-excitation of periodic grain vibrations at 10-100 GHz is shown to be possible for a sufficiently large bias voltage leading to a novel 'shuttle mechanism' of discrete charg e transfer and a current through the nanostructure proportional to the vibr ation frequency. For the case of weak electromechanical coupling an analyti cal approach is developed which together with Monte Carlo simulations shows that the shuttle instability for structures with high junction resistances leads to hysteresis in the current-voltage characteristics. (C) 1998 Elsev ier Science B.V. All rights reserved.