Within the framework of a solid-on-solid model we have derived expressions for  and  step free energies of a simple square (001) surface. We show that at elevated temperatures overhangs in the steps cannot be ignored. With increasing temperature, the free energy curves of  and  steps nicely collapse onto each other. This means that (1) the two-dimensional equilibrium shape of an ad-atom island or vacancy island will exhibit a perfectly circular shape at elevated temperatures and (2) the step free energies vanishes at the same temperature leading to an isotropic thermal roughening of the (001) surface.
|Number of pages||4|
|Journal||Physics letters A|
|Publication status||Published - 2004|