Department of Physics, University of Washington,
Seattle, Washington 98195-1560
The (001) facets of Si and Ge have an uniaxial structure which changes
direction at each mono-atomic step.
This type of topology is unusual and new for the theory of surface
roughening and reconstruction phase transitions.
It can be incorporated into the solid-on-solid model description.
The phase diagram includes preroughening transitions and
disordered flat phases without the need for step-step interactions.
The competition between this and the 1x2 reconstruction in Si(001)
can be described by a generalized 4-state clock-step model.
This leads to the prediction that Si(001) and Ge(001) undergo a
preroughening induced simultaneous deconstruction transition.