Nonequilibrium Interface Dynamics:
Fundamental Physical Issues in Nonequilibrium Interface Dynamics

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Asymmetry and Subtleties of Step Stiffness: Novel Findings and Their Implications

Dr. Theodore L. Einstein

Department of Physics, University of Maryland

Abstract:   Comparison with experiment for Cu(100) shows that the stiffness predicted by the Ising model, using a kink energy deduced from a close-packed direction, underestimates the stiffness by a factor of 4 in general (non-close-packed) directions. Since room temperature is much less than this kink energy, we can make use of the explicit formula coming from a low-T expansion. The low-T formula can be adapted to a triangular lattice, allowing comparison with data for Cu(111). A corollary of this work is that one cannot deduce the step free energy from the stiffness (even though one can readily do the opposite). There are many implications for step fluctuations and electromigration, most obviously that the stiffness is not isotropic, and that the stiffness for steps in the close-packed direction is a particularly poor approximation for the general value. O. Pierre-Louis has found that stiffness asymmetry can lead to interrupted coarsening. S.V. Khare and collaborators have developed a way to analyze island fluctuations on highly anisotropic substrates like TiN. We have followed up on this work. Recent numerical evidence, motivated by study of island fluctuations on Pb(111), suggests that when the asymmetry is not so pronounced and the atomic mass transport is predominantly along the edge, analysis assuming isotropy is adequate and in many ways preferable.

Work supported by NSF MRSEC at U. of Maryland, done in collaboration primarily with T.J. Stasevich and F. Szalma and with E.D. Williams and her group at Maryland, and with M. Giesen, H. Ibach, and S. Dieluweit at FZ-Juelich (via Humboldt Foundation).