The (001) facets of Si and Ge have a uniaxial structure which changed direction at each mono-atomic step. This type of topology was unusual and then new for the theory of surface roughening and reconstruction phase transitions. It could be incorporated into the solid-on-solid model description. The phase diagram included pre-roughening transitions and disordered flat phases without the need for step - step interactions. The competition between this and the 1 x 2 reconstruction in Si(001) could be described by a generalized 4-state clock-step model. This led to the prediction that Si(001) and Ge(001) underwent a pre-roughening induced simultaneous deconstruction transition.

Pre-Roughening Induced Deconstruction in Si and Ge(001) Type Crystal Surfaces. M.den Nijs: Journal of Physics A, 1997, 30[2], 397-404