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NEWS ARCHIVES
For Immediate Release
October 22, 2002
Georgia Tech Physicist Uzi Landman Receives Materials Research Society Award for Studies of Nanoscale Friction and Lubrication
A Georgia Institute of Technology physicist who used powerful computer simulations to predict how friction and lubrication would affect nanometer-scale mechanical systems is one of two scientists who will receive medals December 4 from the Materials Research Society (MRS).
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Uzi
Landman, director of Georgia Tech's Center for Computational Materials
Science, will receive recognition from the MRS, the world's largest materials
professional society. The medal award
is given to recognize "a specific outstanding recent discovery or
advancement that is expected to have a major impact on the progress of
any materials-related field." Charles M. Lieber of Harvard University
will also be honored with a medal at the ceremony.
Landman's award is for the development and implementation of research
methodologies that use molecular dynamics simulations to predict the often-surprising
behavior that occurs at the nanoscale when surfaces of solid and liquid
materials meet. Landman's research team has examined the effects of friction
and lubrication in these small-scale systems, predicting how such systems
would behave long before they could be fabricated. Over time, most of
their key predictions in this new science of nanotribology have been confirmed
experimentally.
Performed on large parallel-processing computers, the simulations use
known laws of physics - including quantum mechanics - to predict how hundreds
of thousands of molecules or atoms interact and respond to external influences
such as the exertion of a load or the application of shear relative motion
between bodies in contact. The resulting calculations will help engineers
design smaller and smaller disk drives, nanometer-scale machines and even
biomechanical implants used in the body.
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A faculty member in Georgia Tech's School
of Physics since 1977 and currently a Regents' and Institute Professor
and Fuller E. Callaway chair, Landman began working on molecular dynamics
simulations in the late 1970s. A 1990 article he published in the journal
Science brought particular attention to the field by "demonstrating
the capacity of realistic molecular dynamics simulations to make specific
predictions that could be compared to quantitative measurements in the
field of tribology," the MRS citation says.
"In many respects, Landman helped create the field of nanotribology
as he contributed to both classical and quantum mechanical molecular dynamics
simulation methodologies, leading to an understanding of the atomic origins
underlying nanoscale tribological processes," the MRS added.
The 1990 Science paper used large-scale molecular dynamics simulations
done on large supercomputers to show that when a nickel tip was brought
into close proximity to a sheet of gold, gold atoms would jump from the
sheet to the probe.
"To our amazement, we found the gold atoms jumping to contact the
nickel probe at short distances," Landman recalled. "Then we
did simulations in which we withdrew the tip after contact and found that
a nanometer-sized wire made of gold was created. That gold would deform
in this manner amazed us, because gold is not supposed to do this."
The simulations were done several years before scientists began to make
and measure the properties of wires on that size scale, and prior to the
rise of the nanoscience and nanotechnology field.
These early simulations and subsequent ones showed that nanometer-scale
wires, called interfacial junctions, would be formed whenever bare metal
surfaces, as well as other material surfaces, were brought into close
proximity. Transforming earlier notions in the microscopic domain, the
simulation results suggested that breaking these junctions is the cause
of friction - resistance to motion - in small-scale mechanical devices.
"It is the need to shear these junctions when you move two bodies
parallel to one another that dissipates energy," Landman noted. "Work
is dissipated and irreversibly lost in the process of formation and breakup
of these junctions. That's what causes the resistance to motion."
Landman also showed that lubricant molecules may no longer behave as
lubricants when trapped in very small gaps between surfaces. Instead,
they organize themselves into "soft crystals" that increase
rather than decrease resistance to motion.
"It turns out that in this kind of a nanotribological situation,
molecules do not behave like they do in bulk," he said. "When
you confine fluids of this type to such small dimensions, they behave
very differently. The viscosity is different, the degree of order is different
and they have a tendency to self-order themselves parallel to the sliding
surfaces. Under such circumstances, the lubricant can become a source
of problems because it is no longer a liquid."
Landman and his group have formulated and simulated techniques that could
be used to maintain the lubricating properties by "frustrating"
the molecules' attempts to align themselves. One strategy would be to
use branch-chain molecules that cannot align themselves into soft crystals.
Another technique would be to rapidly vary the distance between the moving
surfaces, keeping the lubricant molecules in motion - thereby preventing
them from forming soft-solid crystals.
Other simulations showed that nanometer-scale wires would behave like
ideal materials because they are made up of too few atoms to have single
and extended defects known as dislocations. Without defects to impede
the flow of electrons, these wires allow "ballistic electronic transport,"
leading to reduced resistance and quantized conductance. This will be
important to the design of future small-scale electronic devices, Landman
notes.
In August 2000, Landman and collaborator Michael Moseler published a
cover article in Science in which they reported on a molecular
dynamics simulation that predicted the behavior of nanometer-scale jets
of liquid.
The underlying theme behind all of this work can be summed up as "small
is different," the title Landman will use for his MRS medal presentation.
"New behavior emerges on the nanoscale," he explained. "This new behavior creates interesting physical phenomena, and that is where the technological opportunities may lie. To take advantage of them, we must understand how these small systems behave."
Previous releases on Uzi Landman's work:
- Presentation to American Association for the Advancement of Science, February 2001.
- Predicting the Properties of silicon nanowires, September 2001.
- Winning Feynman Prize in Nanotechnology, November 2000.
- Predicting the Performance of Nanojets, August 2000.
- "Frustrating" the Order of Lubricant Molecules, July 1998.
- When a Lubricant May Not Be a Lubricant, October 1995.
- The
Unexpected Properties of Nanowires, March 1995.
RESEARCH NEWS & PUBLICATIONS OFFICE
Georgia Institute of Technology
75 Fifth Street, N.W., Suite 100
Atlanta, Georgia 30308 USA
MEDIA RELATIONS CONTACTS:
John Toon (404-894-6986); E-mail:
john.toon@edi.gatech.edu; Fax: (404-894-4545) or Jane Sanders (404-894-2214);
E-mail: jane.sanders@edi.gatech.edu.
TECHNICAL CONTACT: Uzi Landman (404-894-3368); E-mail: (uzi.landman@physics.gatech.edu).
WRITER: John Toon