Carbon Nanotubes – Polymer Actuators and Field Effect Transistors

Novel and unique phenomena possessing tremendous commercial potential have been discovered in the field of electrical and photo mechanical microactuators by Emitech's team with the support of the University of RI.

Micrograph of a 20×3.5 mm SWNT-Nafion-SWNT cantilever with 0 V bias (left) and with 3.5 V, 28 Hz ac bias (right).

A system composing of an ionomeric polymer (nafion) coated with single-walled carbon nanotube (SWNT) electrodes acts as an electromechanical actuator18a. The actuator gives a sizable mechanical response to low voltages under open-air conditions. The actuator is active under both DC and AC bias and has a strong resonance at low frequencies that is dependent upon the size of the actuator. Remarkably, such a device demonstrates a very long actuation lifetime, much longer than any existing polymer or only carbon nanotube based actuators.

The left micrograph shows a nafion (180 µm)/ SWNT(15µm) bilayer prior to light exposure and the right micrograph shows the same cantilever under illumination of ~ 100 mW/cm2 white light after 20s. 9a

Photomechanical actuators16a is the next scientific and technological breakthrough discovered by Emitech's team. It was found a strong mechanical response of nafion-SWNT composite on visible-NIR light of low intensity. The figure shows the cantilever displacement on the sub-mm scale under light illumination. Also, you can watch the movie [below, right; use slider to fast forward], demonstrating the cantilever movement induced by light. Such a unique photomechanical actuation effect is new and its nature is principally distinctive from existing photostrictive mechanisms in semiconductors, polymers/gels and carbon nanotubes. A cantilever tip displacement can be considered as a gigantic photo elastic response (up to one mm) with respect to semiconductors (several tens nm) at the same conditions.

Flexible field effect transistors (FETs) were fabricated from similar composite material demonstrating an excellent gating effect15a. To our knowledge, this is the first report about a SWNT based FET fabricated in a micro format with extremely thick SWNT film (10 µm ) and an insulating layer ( ~ 180 µm nafion membrane ). The image on the home page shows the schematic of our flexible field effect transistor fabricated from SWNT- nafion composite.