Here we develop methods for fabrication of large-scale arrays of carbon nanotube-based nanoelectromechanical systems (NEMS) and investigate failure modes common to a class of related nanotube/nanowire-based devices. We use a carbon nanotube-based switch with closed-loop feedback control, developed by our group, as a platform for our investigations. Ultimately we strive to establish a metric for the design and construction of robust carbon nanotube-based NEMS.

Each switch consists of a multi-walled carbon nanotube fixed at one end to a top electrode and cantilevered over a bottom electrode for electrostatic actuation. The actuation circuit includes a voltage source and a feedback resistor. Electromechanical models, which include considerations for charge concentration at the tip of the nanotube and van der Waals forces, predict two well-defined stable equilibrium positions as a result of current tunneling and incorporation of a feedback resistor in the circuit. These pull-in/pull-out and tunneling characteristics have been confirmed experimentally by means of in-situ SEM experiments. In the process of our experimental characterization of the nanotube switch, we observed several failure modes which appear common to other related nanotube and nanowire-based NEMS. Potential applications of the device include NEMS switches, random-access memory elements, logic devices, electron counters and gap sensing devices.

Our current efforts include:

1. development of methods for building large-scale arrays of these devices using a combination of standard micro/nanofabrication techniques and directed self-assembly of carbon nanotubes, and
2. investigating failure modes common to the feedback-controlled switch and similar nanotube/nanowire-based NEMS. We use the feedback-controlled switch as a platform for both of these investigations.

Failure Modes

A host of failure modes currently preclude fabrication of robust, large-scale arrays of nanotube/nanowire-based NEMS for commercial applications. These failure modes include fracture or ablation of the nanostructures and irreversible stiction. Using the feedback-controlled switch as a platform to investigate these failure modes, we are building devices with incrementally-varying geometry (using the fabrication methods described above) to conduct a parametric study of the design space. Combining this with multi-scale models, we investigate the underlying mechanisms for the observed failures in an effort to establish a metric for robust design of nanotube or nanowire-based NEMS.

Personnel

• H.D. Espinosa (PI)
• O. Loh (Graduate Student)

Collaborators

• John Sullivan (Center for Integrated Nanotechnologies, Sandia National Labs)
• Ralu Divan (Center for Nanoscale Materials, Argonne National Labs)

Selected Publications

• C.-H. Ke and H.D. Espinosa. "In situ Electron Microscopy Electromechanical Characterization of a Bistable NEMS Device," Small, Vol. 2, No. 12, p. 1484-1489, 2006.

• C.-H. Ke, N. Pugno, B. Peng and H.D. Espinosa. "Experiments and Modeling of Nanotube NEMS Devices," Journal of the Mechanics and Physics of Solids,Vol.53, pp.1314-1333, 2005.

• C.-H. Ke, H.D. Espinosa, and N. Pugno. "Numerical Analysis of Nanotube Based NEMS Devices. Part II: Role of Finite Kinematics, Stretching and Charge Concentrations." Journal of Applied Mechanics, Vol. 72, pp.726-731, 2005.

• C.-H. Ke and H.D. Espinosa. "Numerical Analysis of Nanotube Based NEMS Devices. Part I: Electrostatic Charge Distribution on Multiwalled Nanotubes," Journal of Applied Mechanics, Vol.72, pp.721-725, 2005.

• N. Pugno, C.-H. Ke, and H. D. Espinosa. "Analysis of doubly-clamped nanotube devices in finite deformation regime," Journal of Applied Mechanics, Vol. 72, pp.445-449, 2005.

• C.-H. Ke and H.D. Espinosa. "Feedback Controlled Nanocantilever Device," Applied Physics Letters, Vol. 85, pp. 681-683, 2004.

Patents

• H.D. Espinosa, C-H. Ke, "Nanocantilever Bistable Tunneling Proximity Sensor/Probe." NU Disclosure No. 24071, (US patent application filed in 2005).