nanoquebec 2007-08-19 09:17
Actuators get tuned on the nanoscale
[size=5][b]Actuators get tuned on the nanoscale[/b][/size]
[b][纳米科技世界快讯]A nanomechanical resonator that converts electrical energy into mechanical strain using a highly efficient, tuneable actuation mechanism based on the piezoelectric effect has been developed by researchers in the US. The mechanism, which is radically different to that employed in previous nanoelectromechanical systems (NEMS), could find use in a variety of applications, including nanomechanical arrays for chemicals sensing, high-speed switches and nanomechanical logic-based[/b] computation.
"Most research on NEMS so far has focused on the challenging task of converting tiny mechanical vibrations into a measurable electrical signal," team member Sotiris Masmanidis of the California Institute of Technology told nanotechweb.org. "We saw an opportunity to explore the opposite phenomenon – converting electricity into a nanomechanical strain, using the piezoelectric effect that is found in certain crystals."
[img]http://img247.imageshack.us/img247/6407/0708152e84080fr3.jpg[/img]
[i]The cantilever used to explore depletion-mediated actuation. The scalebar on the bottom right is 1 micron. The structure consists of threelayers of gallium arsenide arranged vertically in ap-type/intrinsic/n-type diode configuration. (Credit: S Masmanidis)[/i]
The structural layer in the new device consists of a 200 nm thick diode made from gallium arsenide. Using standard nanofabrication techniques, Masmanidis and colleagues fashioned this diode into cantilevers, or doubly clamped beams. The researchers found that by applying a small oscillating voltage across the diode under a suitable range of frequencies, they could excite the device into mechanical resonance.
"We saw that these structures are not only very efficiently actuated by piezoelectricity, but that they give rise to behaviour that is only prevalent in nanoscale devices, whose thickness approaches the 'depletion width' of diodes," said Masmanidis.
In particular, the actuation efficiency can be tuned using a DC voltage applied along with the oscillating voltage. This is possible because the piezoelectric strain is concentrated in the diode's depletion region (an insulating layer in the semiconductor where charge carriers are depleted), whose width depends on voltage. The result represents a novel way of tailoring the mechanical behaviour of nanoscale devices by exploiting their intrinsic material properties, explains Masmanidis.
The result is possible thanks to the depletion-mediated actuation effect in piezoelectric semiconductor nanostructures. "Other piezoelectric devices have well-defined electrodes and piezoelectrically active layers," explained Masmanidis. "But in the semiconducting systems we investigated, the boundary between the electrode and active region is blurred by charge depletion, giving rise to new electromechanical coupling phenomena."
The researchers say they would now like to apply this "unique toolbox for designing nanomechanical systems" to the study of more-complex devices, such as arrays of interacting NEMS resonators. "We'd also like to explore other piezoelectric semiconductor materials such as aluminium nitride, which has superior mechanical and electrical properties over gallium arsenide," added Masmanidis.
The team published its work in [url=http://www.sciencemag.org/cgi/content/abstract/317/5839/780][i]Science[/i] [b]317[/b] 780[/url].
Source: Nanotechweb