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Physics Colloquium
Friday, September 2nd, 2005, 4:00 P.M.

E300 Math/Science Center; Refreshments at 3:30 P.M. in Room E200

Min Zhou

Georgia Institute of Technology

Novel Shape Memory of Metal Nanowires

Shape memory materials have important applications because of their ability to recover certain configurations under proper thermomechanical conditions. They are sometimes referred to as ¡Èsmart materials¡É because they can function simultaneously as sensors and actuators. Until recently, the shape memory effect (SME) and its underlying pseudoelasticity were considered unique to shape memory alloys (SMAs), liquid crystal elastomers, and piezoelectric ceramics. Recent research has shown that pseudoelasticity may also be found at the nanoscale, in gold nanowires and carbon nanotubes. Here, we report the discovery of a novel SME in a class of single-crystalline metal nanowires (including Cu, Au, Pt, Ni, and Ag) with sizes smaller than approximately 10 nm. This behavior arises from a reversible crystallographic lattice reorientation within the face-centered cubic (FCC) crystalline structure and is driven by the surface stress and high surface-to-volume ratios of the one-dimensional nanomaterials, a unique and hitherto unknown mechanism which is different from that for SMAs. This SME exists over a wide range of temperature and is associated with response times on the order of nanoseconds, making the nanowires attractive functional components for a new generation of biosensors, transducers, and interconnects in nano-electromechanical systems (NEMS).

Dr. Zhou is a professor in the School of Mechanical Engineering and School of Materials Science and Engineering at Georgia Tech. His research focuses on the behavior of materials at several length scales, emphasizing computational modeling with molecular dynamics simulations, finite element methods, and experiments with laser interferometry and digital diagnostics. He received the NSF CAREER award in 2000 and the Sigma Xi Best Paper Award in 2004. He was named a Woodruff Faculty Fellow at Georgia Tech in 2004 and was elected a Fellow of the American Society of Mechanical Engineers in 2005. He is an associate editor for the Journal of Engineering Materials and Technology.

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