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Surface Stress and its Importance to Nano-structured Materials
Surface Stress and its Importance to Nano-structured Materials Properties of solid surfaces have received renewed interest, as they influence properties and applications of nano-structured materials. In particular, one such property is the surface stress or surface tension of solids. The conventional and widely publicized definition of surface stress is due to Shuttleworth. However, the validity of this definition has been repeatedly questioned in the literature, and it remains a controversial issue. An alternate definition and approach to surface stress and surface elasticity has been published by Gurtin and Murdoch, based on the principles of continuum mechanics and their rigorous mathematical formulation. We have applied their theory to re-analyze experimental data on lattice parameter changes in solid nano-particles, and to compare its predictions with results from atomistic and first-principle simulations of thin films, of atomic clusters, and of vacancy clusters in metals. We find that the Gurtin-Murdoch theory provides an excellent description of the experimental findings and of the results from atomistic simulations. Measured lattice parameter changes as a function of particle size enable us to determine values for the residual or intrinsic surface stress and the surface stretch modulus, two important surface properties in the Gurtin-Murdoch theory. Our demonstration of the success of this theory indicates that the Shuttleworth definition is inappropriate if not incorrect. Biosketch: Wilhelm G. Wolfer is presently a consultant to Sandia National Laboratories in areas of shock physics, hydrogen storage in materials, and mechanical properties of materials. Previously, he was a program leader for plutonium aging in the Chemistry and Materials Science Directorate at Lawrence Livermore National Laboratory. Before joining this laboratory in 1997, he was Manager of the Computational Materials Science Department at Sandia National Laboratory, California. He obtained his degree in Physics at the Max Planck Institute in Stuttgart, Germany, and his PhD in Nuclear Engineering Sciences from the University of Florida, Gainesville. He spent four years at the Advanced Reactor Division of Westinghouse, and two years at the Oak Ridge National Laboratory before joining the University of Wisconsin in 1976 as a Professor of Nuclear Engineering. In 1979, he was a Visiting Scientist at the Max-Planck Institute for Plasma Physics, Garching, Germany. His research interests are in radiation damage in materials, properties of defects in solids, theory and modeling of solid state reactions, phase transformations, and microstructural evolution during processing of materials.
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