Nonresonant high-frequency actuation of carbon based nanoelectromechanical oscillators

Licentiatavhandling, 2015

Carbon based nanoelectromechanical oscillators outperform their predecessors in many ways. In particular, their extraordinarily high quality factors make them very promising for sensor applications. To operate the nano oscillators, different kinds of actuation mechanisms are utilised, for instance direct or parametric resonance. Nonresonant actuation of the mechanical vibrations can be achieved if the oscillator is integrated in a resonant LC-circuit or an optomechanical cavity resonator. In these nonresonant actuation mechanisms, the external field couples to the resonance properties of the LC-circuit and optomechanical cavity. The resonance frequencies are typically orders of magnitude higher than the frequencies of the mechanical vibrations. In this thesis, nonresonant actuation of mechanical vibrations by high-frequency electrical fields are investigated analytically in three different nanoelectromechanical oscillators. Firstly, I analyse a graphene oscillator which is integrated in an RC-circuit which lacks the resonance of an LC-circuit. Secondly, an isolated graphene oscillator where the electrodynamics is determined by the internal properties of the graphene sheet is considered. Finally, I analyse a movable single-electron quantum dot in tunnel contact with an electron reservoir. The simple capacitance, hydrodynamic and tunneling models used to describe the systems demonstrate the possibility to nonresonantly actuate mechanical vibrations by high-frequency electrical fields. The mechanism is due to the time-delayed electromechanical feedback when the system is driven above the characteristic frequency of the electronic subsystem. Further, nonlinear dissipation is investigated as one possible saturation mechanism of the unstable mechanical motion. The actuation of mechanical vibrations of the isolated graphene sheet is particularly interesting. In this system a geometric resonance of the induced charge oscillations and the vibrational modes seems to allow nonresonant selective actuation of several modes, despite the fact that the driving field is homogeneous.