CONTINUUM MODEL FOR SURFACE RECONSTRUCTIONS IN (111)-ORIENTED AND (100)-ORIENTED SURFACES OF FCC METALS

A continuum model for surface reconstructions in fcc metals is presented. The energetics associated with the relaxation of a surface that is elastically strained due to the surface stress, resulting in a loss of structural coherence with the underlying bulk, are analyzed. A simple criterion is developed that involves a dimensionless parameter beta = (f - gamma)/mub, where f and gamma are the surface stress and surface tension of the unreconstructed surface, mu is the shear modulus, and b is the magnitude of the Burgers vector. The model predicts that when beta exceeds a critical threshold, the surface should reconstruct. It is shown that the predictions from the model are in general agreement with experimental observations for both (111) and (100) oriented surfaces. The model also predicts that the (111) oriented surface of Pb may display a surface reconstruction at high temperature as has recently been reported for the (111) surface of Pt. The analysis for the (100) oriented surfaces suggests that while there may be a thermodynamic driving force for reconstruction, it is necessary to enhance the kinetics of the transformation through effects of the surface stress (or of an externally applied stress).