Uzi Landman and Kevin Brennan study devices and structures that are at the limits of today's technology. Using powerful computer simulations based on established physical principles, they explore the world of the very small to provide guidance for tomorrow's device designers – suggesting appropriate materials, warning of pitfalls and recommending routes to avoid.
photo by Gary Meek
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Simulations based on established physical principles help researchers understand the unusual behavior of materials at the nanoscale. Uzi Landman pioneered the use of supercomputer-based molecular dynamics simulations to study the unique properties of nanowires, nanojets and other structures.
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Director of the Center for Computational Materials Science and a professor of physics, Landman relies on supercomputers to understand how thousands of atoms and molecules interact under the influence of quantum mechanics. He and his research team examine how wires just a few atoms in diameter will behave, what might be necessary to operate nanoscale jets and how unique molecular effects may hamper lubrication in tiny machines.
"Atomistic simulation methods allow interrogations of complex materials systems with a resolution in space and time that is often not possible by other theoretical approaches," he explains. "In such 'numerical experiments,' researchers can investigate the behavior of matter under conditions that are sometimes difficult, hazardous or impossible to realize in the laboratory."
The simulations often show dramatic differences between materials at the nanoscale and those same materials at more familiar-size scales. Landman adds, "Small really is different."
Among the predictions from his molecular dynamics simulations:
- Liquid jets just a few nanometers in diameter should be technically possible, though their propagation will differ from larger jets and require special operating conditions.
- Highly confined fluids composed of molecular mixtures segregate themselves by size, with longer-chain molecules adsorbing near the surfaces and smaller ones remaining in the center of the confining gap.
- Building nanowires from clusters of silicon atoms, rather than atom-by-atom, could solve the statistical problems involved in doping silicon to improve its properties at the small scale.
With more than a decade of experience simulating small structures, Landman has now seen many of his predictions borne out as experiment catches up with theory. In November, he won the Feynman Prize in Nanotechnology (Experimental) for pioneering work in computational materials science.
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Molecular dynamics simulations show unusual behavior of lubricant molecules in confined spaces.
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Brennan, a professor in the School of Electrical and Computer Engineering, studies the unique properties of next-generation compound semiconductors. His work on electron transport, failure modes and other effects will help nanoelectronic device designers of the future choose the right materials.
While Brennan focuses primarily on wide band-gap materials for high-powered, high-frequency telecommunications devices, his predictions also apply to traditional silicon.
"We start from the fundamental physical principles of the electronic structure and calculate what happens as electrons move through the crystal and interact with the lattice," he explains. "We can put all of the factors into our simulator and predict with reasonable certainty what the electrons are really experiencing. From there, we can move to device geometry and explain how the device is going to behave. This is particularly important in nanostructures as we miniaturize devices."
Designers must be able to anticipate device behavior under different conditions as they produce smaller microcircuits operating with higher electric field strengths. To handle those fields without breaking down or producing unpredictable behavior, new materials such as gallium nitride and silicon carbide will be needed. The information Brennan's group develops will help designers understand the trade-offs between device properties in these new materials – and suggest the most promising experimental routes for learning about them.
"We are the point people, out in front of the device designers, trying to understand what will be going on," he says. "We're helping choose the optimal routes to follow in selecting materials and building devices to minimize the cost and improve performance."
For more information, contact Uzi Landman, School of Physics, Georgia Tech, Atlanta, GA 30332-0430. (Telephone: 404-894-3368)
(E-mail: uzi.landman@physics.gatech.edu); or Kevin Brennan, School of Electrical and Computer Engineering, Georgia Tech, Atlanta, GA 30332-0269. (Telephone: 404-894-6767)
(E-mail: kevin.brennan@ece.gatech.edu)
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Last updated: July 14, 2001
