Experiments and modeling of carbon nanotube-based NEMS devices

In this paper, carbon nanotube-based nanoelectromechanical systems (NEMS) are nanofabricated and tested. In-situ scanning electron microscopy measurements of the deflection of the cantilever under electrostatic actuation are reported. In particular, a cantilever nanotube suspended over an electrode (nanoswitch), or two symmetric cantilever nanotubes (nanotweezers), from which a differential in electrical potential is imposed, are studied. The finite deformation regime investigated here is the first of its kind. An analytical model based on the energy method in both small deformation and finite kinematics (large deformation) regimes is used to interpret the measurements. The theory overcomes limitations of prior analysis reported in the literature towards the prediction of the structural behavior of NEMS. Some of the simplifying hypotheses have been removed. Furthermore, the theory takes into account the cylindrical shape of the deflected nanotube in the evaluation of its electrical capacitance, the influence of the van der Waals forces as well as finite kinematics. In addition, tip charge concentration and a quantum correction of the electrical capacitance are also considered. The energy-based method is used to predict the structural behavior and instability of the nanotube, corresponding to the on/off states of the nanoswitch, or to the open/close states of the nanotweezers-at the so-called pull-in voltage. Accuracy of the derived formulas is assessed by comparison of the theoretical prediction and experimental data in both small deformation and finite kinematics regimes. The results reported in this work are particularly useful in the characterization of the electromechanical properties of nanotubes as well as in the optimal design of nanotube-based NEMS devices.