AVS 53rd International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuA

Paper SS1-TuA8
Anisotropy in the Continuum Step Model: From Step Stiffness to Step-Edge Mobility*

Tuesday, November 14, 2006, 4:20 pm, Room 2002

Session: Surface Structure and Morphology
Presenter: T.J. Stasevich, University of Maryland
Authors: T.J. Stasevich, University of Maryland
C. Tao, University of Maryland
E.D. Williams, University of Maryland
T.L. Einstein, University of Maryland
Correspondent: Click to Email
The evolution of vicinal surfaces can be efficiently simulated using the continuum step model.@footnote 1@ An important model parameter is the step stiffness, which quantifies how easily a step fluctuates and responds to driving forces. Due to the underlying crystal structure of vicinal surfaces, the stiffness can depend sensitively on step orientation, especially at temperatures low compared to the surface roughening transition (for noble metals, room temperature is considered low). Analytically accounting for this anisotropy within a lattice-gas framework is challenging, making direct comparisons with experiment or implementation in simulations time-consuming and computationally demanding. In this talk, we discuss simple, low-temperature approximations for the stiffness anisotropy on both {001} and {111} surfaces.@footnote 2@ These approximations only fail for steps aligned close to the high-symmetry direction, where an exact, explicit solution can fortunately be obtained. We exploit this by combining our simple formulas with small-angle expansions of the high-symmetry solutions, producing explicit, analytic approximations for the full anisotropy of step stiffness, accurate at nearly all experimentally relevant temperatures. We have recently implemented our formulas into finite-element simulations of the continuum step model. To make contact with experiment, we simulate the relaxation of a Ag(111) step initially pinned by surface impurities. By STM scanning, one pinning point was removed, and the step was thereafter observed to relax to a more favorable configuration. Matching our simulation to the experiment allows us to extract information about the adatom step-edge mobility,@footnote 3@ a parameter traditionally difficult to isolate. @FootnoteText@ *Work supported by NSF-MRSEC at UMD.@footnote 1@Jeong and Williams, Surf. Sci. Rep. 34, 171 (1999).@footnote 2@Stasevich et al., PRB 70, 245404 (2004) and PRB 71, 245414 (2005).@footnote 3@Tao et al., PRB 73, 125436 (2006).