Continuous and discontinuous transitions on 3D equilibrium crystal shapes:A new look at Pb and Au

Equilibrium crystal shapes exhibit flat facets and rough vicinal surfaces. with transitions between them being either continuous or discontinuous, the latter recognizable by a sharp edge. In general, mixed repulsive/attractiv e step-step interactions may lead to continuous or discontinuous facet-to-v icinal transitions. In can be shown that the contact angle at the facet for a discontinuous transition is directly related to the ratio of the step in teraction strengths. Alternatively, surface reconstruction of facets can al so be responsible for sharp edges at the facet boundary. In this case the c ontact angle is related to the difference between surface free energies of the reconstructed and unreconstructed facet as well as the corresponding di fference of step interaction energies. Fitting the experimental shapes by t heoretical expressions can be used to extract the relevant surface and step free energies and also step interaction energies. Experimental examples of Pb and Au equilibrium shapes are evaluated and discussed. Step free energi es of vicinal Au(1 1 1) and Au(1 0 0) surfaces, evaluated by both models, a re 30 and 10 meV/A(2), respectively. (C) 2001 Elsevier Science B.V. All rig hts reserved.