RESEARCHERS FIND WAY TO MEASURE FRICTION ON AN ATOMIC LEVEL
COLUMBUS, Ohio -- Researchers here have successfully measured the resistance of one atom as it rubs against another, using new techniques that are rewriting our understanding of the laws of friction. This and other accomplishments are all part of a new and rapid-paced field of nanotribology discussed in the latest issue of the British science journal Nature.
One goal of such research teams is the production of perfectly smooth surfaces. If those are possible, it could lead to as much as a 400-fold increase in the ability to store digital data on magnetic tape and on computer disk drives.
Bharat Bhushan, an Ohio Eminent Scholar and director of the Computer Microtribology and Contamination Laboratory at Ohio State University, said that the new field is providing important clues about what happens between individual atoms and molecules when two surfaces meet.
Jacob N. Israelachvili, professor of chemical and nuclear engineering at the University of California at Santa Barbara, and Uzi Landman, professor of physics at Georgia Institute of Technology, are co-authors of the paper.
For years, scientists have tried to understand just what happens when materials rub against each other, what role friction plays, and how different compounds withstand constant abrasion. For the most part, their theories were based on conjecture and predictions -- not observable facts.
But now with the advent of several new technologies, researchers are able to watch as individual atoms move past one another, scarring the differing surfaces and exchanging molecules from one compound to another.
"The old law of friction -- Amontons Law, the one that's in all the textbooks -- says that the coefficient of friction is independent of the apparent area of contact and normal load. We found that this simply isn't true," Bhushan said. "The old laws are not valid in these situations, so new theories of friction are emerging."
The realm in which Bhushan and his colleagues are operating is the world of nanotechnology, an arena where the thickness of a human hair -- 75,000 nanometers -- is gargantuan compared to the thickness of surfaces and the depth of scratches on the materials he is using. He uses two techniques -- AFM, atomic force microscopy, and FFM, friction force microscopy -- to test the smoothness of ultrasmooth surfaces and to gauge the resistance that can be caused by microscopic defects in those surfaces.
While their findings do have a bearing on the microscopic motors and actuators which have brought public attention to the field of nanotechnology, Bhushan's main interest is the potential the new information has for the design of computer disk drives and other magnetic storage devices. With current technology, information is retrieved by heads that move over the surface of ultrasmooth aluminum disks spinning at incredible speeds.
"It's the equivalent of a jet airliner flying full speed only a few inches off the ground," Bhushan said. "I'm trying to develop a way to get perfectly smooth recording media over which a recording head could fly as close as possible, perhaps even be in contact with the surface!"
If that were done, it would have enormous ramifications for the computer and recording industries. It could mean reducing the size required for a recording head by nearly 1 million times. It could also mean as much as a 400-fold increase in the storage density of computer drives, compared to what is now available, Bhushan said.
He believes such improvements might be possible within the next five years.
Bhushan and his colleagues also reported new developments in lubricating nanotechnology components. They chemically deposited layers of films that were one molecule thick (about two nanometers) onto the surfaces of superfinished aluminum. Then, they took an instrument with a very fine tip and tested how well the surfaces withstood wear.
"We got results that showed the monomolecular film withstood wear about 80 times greater than what might have been expected and they still showed no wear. That's equivalent to what you'd expect with a gold or silica surface," he said.
"This is a new approach to lubricating nanocomponents: the thin film layers are the lubricant; friction is very low;, we get very little wear; and the processes that deposit the films are very simple to do."
Bhushan said that the entire field of nanotribology is only two to three years old and already it represents an industry worth hundreds of billions of dollars. His research is sponsored by the federal Office of Naval Research, the federal Advanced Research Projects Agency and the National Storage Industry Consortium.
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Contact: Bharat Bhushan (614) 292-0651
Written by Earle Holland, (614) 292-8384
EDITOR'S NOTE: Photomicrographs depicting some of Dr. Bhushan's advances are available upon request, including some image files.