  Networks of steps, seen in STM observations of vicinal surfaces on Au and Pt
(110), are analyzed. A simple model is introduced for the calculation of the
free energy of the networks as function of the slope parameters, valid at low
step densities. It predicts that the networks are unstable, or at least
metastable, against faceting and gives an equilibrium crystal shape with sharp
edges either between the (110) facet and rounded regions or between two rounded
regions. Experimental observations of the equilibrium shapes of Au or Pt
crystals at sufficiently low temperatures, i.e. below the deconstruction
temperature of the (110) facet, could check the validity of these predictions.
