Researchers Measure Friction on an Atomic Level

RESEARCHERS MEASURE FRICTION ON AN ATOMIC LEVEL,
MIGHT LEAD TO BETTER COMPUTER DISK DRIVES

     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.

                                #

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.)


[Submitted by: Von Reid-Vargas (ereid@magnus.acs.ohio-state.edu)
               
Thu, 13 Apr 1995 11:23:20 -0400]
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