OAK RIDGE, Tenn., Oct. 7, 1996 --Thanks to a problem with a high-tech microscope, researchers at the Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL) have developed microscopic sensors. These hairlike, silicon-based devices are at least 1,000 times more sensitive and 1,000 times smaller than currently used sensors. Each microsensor spans the width of a human hair.
They can detect and measure relative humidity, temperature, pressure, flow,
viscosity, sound, natural gas, mercury vapor, and ultraviolet and infrared
radiation. They show potential as biosensors Microcantilevers of silicon or silicon nitride have been made that are smaller
than this period. These "microscopic diving boards" project from miniature chips
about the size of a grain of rice. For this innovation of microminiature
sensors, ORNL developers Thundat, Eric Wachter, Mitch Doktycz, Rick Oden, and
Bruce Warmack, all in HSRD, were elected to the International Hall of Fame of
the Inventors Clubs of America. ORNL's microcantilever sensor technology
received an R&D 100 Award from R&D Magazine. The awards recognize the year's
most significant technological innovations.
"We showed that a microcantilever would bend in a measurable way if its tip is
coated with a material that attracts another material from the air," Warmack
says, "For example, a gold-coated cantilever absorbs mercury vapor, which
stiffens the cantilever, causing it to bend and changing the way it vibrates. A
gelatin tip absorbs water, measuring humidity."
"These sensors can also respond sensitively to heat," Thundat says. "A silicon
microcantilever coated with aluminum bends more with rising temperature because
aluminum expands more than silicon. Such a device can measure temperature and
even detect infrared radiation and heat-generating chemical reactions."
When set in motion, microcantilevers have a natural vibration that changes in
the presence of sound waves or a fluid (enabling measurements of viscosity and
pressure).
Changes in cantilever position or vibration rate can be detected by measuring
wobble in reflected laser beams. "Future silicon devices," Warmack says, "will
probably be based on piezoresistance ORNL, one of the Department of Energy's multiprogram national research and
development facilities, is managed by Lockheed Martin Energy Research.
(Photo of Thomas Thundat with microminiature sensor available on request)
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Written by Carolyn Krause