Crystal symmetry, step-edge diffusion, and unstable growth

We study the effect of crystal symmetry and step-edge diffusion on the surface current governing the evolution of a grouping crystal surface. We find there are two possible contributions to anisotropic currents, which both lead to the destabilization of the flat surface: terrace current j(t), which is parallel to the slope m=del z(x,t), and step current j(s), which has components parallel (j(s)(ii)) and perpendicular (js(perpendicular to)) to the slope. On a high-symmetry surface, terrace and step currents are generically singular at zero slope. and this does not allow one to perform the standard linear stability analysis. As far as a one-dimensional profile is considered, j(s)perpendicular to is irrelevant and j(s)(parallel to) suggests that mound sides align along [110] and [110] axes. On a vicinal surface, j(s) destabilizes against step bunching; its effect against step meandering depends on the step orientation, in agreement with the recent findings by Pierre-Louis et al. [Phys. Rev. Lett. 82 (1999) 3661]. (C) 2000 Elsevier Science B.V. All rights reserved.