*Device allows naked eye to see motion of 10 nanometers*
*Sandia creates motion detector 1,000 times more sensitive than any known*
Nanomeasure *Sandia researcher Bianca Keeler studies very fine motion
formerly unobservable by human eye but now revealed by a laser beam
interacting with an unusual diffraction grating fabricated at Sandia's
Microelectronic Development Laboratory.*
*Download 300dpi JPEG image, 'nanomeasure.jpg', 684K
<http://www.sandia.gov/news-center/news-releases/2004/images/jpg/nanomeasure.jpg>*
(Media are welcome to download/publish this image with related news
stories.)
ALBUQUERQUE, N.M. -- A new class of very small handheld devices can
detect motion a thousand times more subtly than any tool known.
"There was nothing in the [optics] literature to predict that this would
happen," says Sandia National Laboratories researcher Dustin Carr of his
group's device, which reflects a bright light from a very small moving
object.
Sandia is a National Nuclear Security Administration laboratory.
Carr, who earlier gained fame as a graduate student at Cornell for his
creation of a nanoguitar, was selected this week by MIT's science
magazine /Technology Review/ as one of the year's top 100 researchers
under the age of 35.
The patent-applied-for device will be the subject of an invited talk at
the SPIE Optics East convention in Philadelphia in October, delivered by
Sandia team member Bianca Keeler.
Like shadow pictures projected onto a wall by shining light through the
fingers of one hand moving over the fingers of the other, the relatively
simple measuring device depends upon a formerly unrecognized property of
optics: light diffracted from very small gratings that move very small
lateral distances undergoes a relatively big, and thus easily
measurable, change in reflection. A motion of 10 nanometers can be seen
by the naked eye, says Carr.
A nanometer is one-thousandth of a micron, which is one millionth of a
meter.
As for the device, size matters and small is crucial. "In standard MEMS
[microelectromechanical] applications, though the devices are small,
very few things that sell are dominated by a search for further
miniaturization. There's not a motivation in MEMS to make things still
smaller as a matter of cost. Economics of scale for integrated circuits
just don't apply to MEMS. But our device couldn't exist unless you made
it this small," he says. Features are in the 100-200 nanometer range,
with 300 nm between top and bottom combs and 600 to 900 nm between comb
teeth.
Sub-wavelength interference effects cause the visual display.
"Making use of the effect is fairly obvious once you realize it
happens," he says.
Fabricated out of polysilicon by standard lithography techniques like
those used to make MEMS devices, the Sandia system uses two tiny
comb-like structures (instead of fingers) laid one over each other. The
bottom comb is locked rigidly in place. The top comb is secured only by
horizontal springs. Any tiny motion sends the top comb skittering over
the bottom comb, laterally deforming the grating. A very tiny
disturbance changes by an unexpectedly large amount the amplitude of
light -- in the visible to near-infrared range -- diffracted from a tiny
laser beam shining upon the apparatus.
Micrograph of device *SEM (scanning electron micrograph) of the device,
with scale bar at bottom representing 10 microns. The top grating layer
is suspended by 4 springs and actuated by two side comb drives. The
second, fixed grating layer is hidden below the first. The area of the
grating itself is 10 microns x 10 microns.*
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<http://www.sandia.gov/news-center/news-releases/2004/images/jpg/grating.jpg>*
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The measuring device, still in the laboratory stage, is in effect a kind
of accelerometer, about the size of the inexpensive
microelectromechanical devices that open automobile air bags. Fabricated
by the same processes that mass-produce silicon computer chips, the
device has multiple possible uses.
"If you can make very sensitive detectors very cheaply and very small,
there are huge applications," says Carr. "Made small, synchronized,
cheap, and placed on every block, we could take data from all these
sensors at once and measure the motion of the earth when there's not an
earthquake. So we could learn what leads up to one."
Another use would be for skid and traction control in cars, detecting if
the back end of the car is moving in a different direction from the
front end.
"Such devices also could take the place of inertial navigation systems,"
Carr says. These typically require large gyroscopes to keep commercial
airplanes moving on a preset course. "We could have handheld-sized
devices on Volkswagens that would work even in a tunnel."
Other defense applications are possible, he says.
He sees a time frame of three to five years before the devices are
available for use.
Says James Walker, former Director of Advanced Technologies at Tellium,
Inc., former manager of the MEMS Network Element Sub-systems Group at
Lucent, Bell Laboratories, and now an independent consultant and patent
agent, "To my understanding, it is the first time anyone has tried to
manipulate the optical near-field region in order to affect changes to
the far-field characteristics of a grating. The ability to do this is a
direct result of the nano-scale nature of the device. Due to its high
responsivity-to-displacement ratio, I see it having significant,
far-reaching application in areas as diverse as chemical sensing,
infrared imaging, accelerometry, and displays."
Sandia is a multiprogram laboratory operated by Sandia Corporation, a
Lockheed Martin company, for the U.S. Department of Energy's National
Nuclear Security Administration. Sandia has major R&D responsibilities
in national security, energy and environmental technologies, and
economic competitiveness.