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UA Researchers Use Nanoscale Speed Bumps to Smooth MEMS, Nano Friction

by Editor1 last modified May 14, 2007 - 19:53

Researchers from the University of Arkansas have shown how nanoscale speed bumps can reduce friction and attractive forces between microscopic parts, helping devices function more smoothly. The work is done at UA’s Nano Mechanics and Tribology Lab, part of UA’s College of Engineering.

UA Researchers Use Nanoscale Speed Bumps to Smooth MEMS, Nano Friction

Reseracher sre using a surface-topography engineering method and water to reduce adhesion and stiction in MEMS and nanoscale devices. "There are two approaches to address adhesion and stiction issues in MEMS devices," said Dr. Min Zou, assistant professor of mechanical engineering. "One is chemistry - applying chemicals on surfaces to weaken the forces. The other is topography engineering. Our approach was simple - we engineered nanoscale bumps to reduce the contact area between surfaces."

Notably, the engineering team used only water, the Laws and Physics and persistent ingenuity to achieve their result. Their work, described in a paper submitted earlier this year to the American Society of Mechanical Engineers’ International Conference on Integration and Commercialization of Micro and Nano-systems. The research was awarded the conference's best paper award.

Using ‘Hydrophobics’ for Tribology
AU project engineers wanted to create a ‘hydrophobic’ surface, where using a water-contact angle water can be beaded up or turned into a ball, much like how water beads up on a car windshield after it has been treated with chemicals or after waxing. [The water-contact angle is the measurement used to describe the extent to which water beads.]

A water-contact angle greater than 90 degrees is considered hydrophobic, and any angle greater than 150 degrees is considered superhydrophobic. With a water-contact angle of approximately 180 degrees, beads represent a near-perfect sphere with only minimal contact on surfaces.

Using only such topography-engineering methods, Zou's team achieved a water-contact angle as high as 137 degrees on silicon. No other researcher has achieved a higher water-contact angle without the use of chemicals. Zou's team also conducted a study that combined the surface-topography engineering method with chemicals. That study achieved a water-contact angle greater than 150 degrees, and thus produced a superhydrophobic surface.

Zou's team started with amorphous silicon - silicon that does not exhibit any crystalline form or shape. The researchers used aluminum to induce crystallization, which manifested as nano- or microcrystallites to form the textured surfaces. The researchers induced crystallization by annealing - a process of heating and cooling - the amorphous silicon in a conventional furnace.

"We demonstrated that the surface area covered by nanotextures can be controlled by changing annealing temperature and duration," Zou said.

In addition to electronic devices, the research applies to biomedical devices. It also advances the understanding of tribology, which is the study of friction, wear and lubrication of interacting surfaces in relative motion, such as gears, bearings and head-disk interfaces in computer hard drives.