Nanoelectromechanical Systems (NEMS) are sensors, actuators and devices with critical dimensions of the order of nanometers. Miniaturizing electromechanical systems a thousand times smaller than MEMS, where critical dimensions are micrometers, have tremendous engineering applications such as ultra-high data storage  or as supersensitive sensors. The design of NEMS can, however, be more challenging compared to the design of MEMS because of new physical phenomena encountered at the nanometer scale.
In this talk we will present results and discuss the development of continuum theories for simulation and design of carbon nanotube based NEMS. Carbon is an attractive material for NEMS because of its structural perfection, excellent electronic and mechanical properties and because of the rapid progress made in the fabrication process of carbon nanostructures. A common approach to simulate NEMS is to use molecular dynamics techniques. However, such approaches can be very expensive and may not be easily integrated in a design process. Hence, in this work we will demonstrate the fruitful use of continuum theories for analysis of NEMS.
We study the pull-in voltage characteristics of a nanotube cantilever over a ground electrode as a prototype NEM device. The pull-in voltage is defined as the potential difference between the cantilever tube and the ground electrode at which the cantilever tube becomes unstable and collapses onto the bottom electrode . Predicting the range of instability is an important design issue for NEM switches as it defines their range of operability. Electromechanical analysis of a nanotube cantilever over a ground electrode has been performed by accounting for three coupled energy domains: elastostatic energy domain, electrostatic energy domain and the van der Waals energy domain. When a potential difference is created between the cantilever and the ground electrode, electrostatic charges are induced on the two conductors. The electrostatic charges give rise to an electrostatic pressure which deflects the cantilever. At nanoscale, the van der Waals forces also need to be taken into account to compute the equilibrium deflection of the nanocantilever structure. A self-consistent solution is obtained when the elastic, electrostatic and the van der Waals forces balance each other. Since there is very limited experimental data on pull-in voltages on NEMS, we will also present results comparing the accuracy of the continuum approach with the results obtained from molecular dynamics simulations.
T. Rueckes et al., Science, 289, 94-97 (2000)
G. Li and N.R. Aluru, Sensors & Actuators, to appear, 2001.
Beckman Institute, University of Illinois at Urbana-Champaign
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