18 Aug Nano-diamond film studied at UW could advance telecommunications
Madison, Wis. – The next generation of high-performance wireless communication devices could rely on crystals, according to engineering researchers at the University of Wisconsin-Madison.
But these are no ordinary crystals. Teams of scientists across the country, pursuing a technology 14 years in the making, are examining a material called ultrananocrystalline diamond and the tiny electromechanical systems into which it could be integrated.
“The purpose of the team is to characterize these nano-crystalline diamond films and fabricate devices out of them to determine whether or not we can create micromechanical and nanomechanical resonator switches,” said Rob Carpick, a professor from the Materials and Mechanics Research Group at the UW-Madison College of Engineering.
Carpick studies mechanics and tribology – the study of friction, adhesion, lubrication, and wear – at the atomic, molecular, and nanometer scale. His skill with advanced scanning force microscopy made him a key collaborator on a joint project to develop this technology.
Argonne National Laboratory leads the project, which has received a $1.4 million award from the Defense Advanced Research Projects Agency, the central research and development organization for the U.S. Department of Defense.
Carpick began working with John Carlisle, a scientist at Argonne who became CTO of Advanced Diamond Technologies, Inc., a start-up company spun off of Argonne that now fabricates the nanocrystalline diamond film.
Tiny diamonds in the rough
The material under investigation is comprised of diamond grains three to five nanometers across and applied to a thin film using a patented process developed at Argonne. The trick will be to modify the material for consistency in a variety of applications such as mechanical pump seals, hermetic coatings for retinal prosthetic implants, and micro-electrical-mechanical systems in telecommunications devices.
Telecommunication applications is where Carpick comes in. Most of the switches and resonators currently utilized in telecommunications devices are made of silicon, but project collaborators have identified crystal as a better candidate material because of its unique physical properties.
“Diamond is stiffer and more environmentally resistant,” Carpick said.
In addition, diamond is highly stable, capable of operating in harsh environments and higher temperatures without degrading, and it demonstrates another important property. A single crystal diamond has the highest acoustic velocity of any material. Since the nanocrystaline form is equally stiff, the film exhibits the same properties.
“High sound speed means high frequency,” Carpick explained. “That’s what you want.”
Optimizing the resonance quality to control for variation can be achieved by tailoring the surface of the diamond resonators at the atomic level, Carpick said. One technique involves applying hydrogen atoms to the surface of the film and cleaning off all the other “chunks” that appear on the surface.
Developing improvements for telecommunications equipment could be incredibly lucrative. According to The Insight Research Corp., the $1.6 trillion telecommunications services and equipment market in 2005 is expected to grow by 21 percent to $1.93 trillion by 2010.
“Given the rate of projected industry growth both in the telecommunications and nanotechnology sectors, the potential for [ultrananocrystalline diamond microelectromechanical systems] is sizable,” said Neil Kane, president of ADT in a release.
In early tests, the diamond film already has shown enormous potential for high-quality performance, and the research could have a far-reaching impact on other sectors, including the defense, industrial, and medical industries.
“Our initial results are very promising,” Carpick said.
Carpick’s lab work
Using the atomic force microscope, Carpick and his team image the surface topography of the film to make basic characterizations about smoothness and other features. Then, with a probe two nanometers across, he measures friction and adhesion.
“[The process] gives you a measure of interfacial bonding and how much it will interact with other materials,” Carpick said. “And if you’re trying to make a device, typically you don’t want it to be sticky.”
Finally, Carpick uses the AFM as a tiny tuning fork to measure resonance frequency. The microscope’s probe, shaped like a rectangular diving board, is shaken to measure the pitch and the duration of the vibrations. An ideal resonator will ring at a high frequency for a long time.
“Cellphones need resonators to filter the signal and purely electronic resonators aren’t that good,” Carpick explained. “The higher the frequency and the higher the quality factor, the better the communication integrity and the more information you can transmit.”
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