Abstract
A (001) surface of silicon consists of terraces of two variants, which have an identical
atomic structure, except for a 90� rotation. We formulate a model to evolve the terraces under
the combined action of electric current and applied strain. The electric current motivates
adatoms to diffuse by a wind force, while the applied strain motivates adatoms to diffuse by
changing the concentration of adatoms in equilibrium with each step. To promote one variant of
terraces over the other, the wind force acts on the anisotropy in diffusivity, and the applied strain
acts on the anisotropy in surface stress. Our model reproduces experimental observations of
stationary states, in which the relative width of the two variants becomes independent of time.
Our model also predicts a new instability, in which a small change in experimental variables (e.g.,
the applied strain and the electric current) may cause a large change in the relative width of the
two variants.