Sinuous step instability on the Si(001) surface

On slightly miscut Si(001) surfaces, straight steps are predicted to be unstable against the formation of long-wavelength undulations. These undulations lower the energy, by, in effect, reducing the size of the stress domains; they are thus analogous to the spontaneous step formation proposed by Alerhand et al. However, step undulations are expected to be kinetically favored, and therefore to preempt spontaneous step formation. Moreover, they lead to an unexpected distinct thermodynamic phase in the surface phase diagram at small angles.