It was pointed out that 4-fold symmetry-breaking at the (001) face of the these crystals resulted in a non-equivalence of surface diffusion in the [110] and [¯110] directions. Various reflection high-energy electron diffraction experiments were suggested for the quantitative study of the anisotropy of surface diffusion. Dimerization of monatomic steps (in the [110] direction) during growth of the vicinal faces of Si and Ge was predicted to occur as a result of the existence of an easy diffusion direction on the (001) surface.

S.Stoyanov: Journal of Crystal Growth, 1989, 94[3], 751-6