Adsorption on stepped substrates

An analysis is given of the behavior of an interface above a stepped substrate in the presence of an external pinning potential for the lattice solid-on-solid (SOS) interface model in 2D. Step-free energy including step-step interaction free energy is calculated, for large step separation. It is found it vanishes at temperatures lower thanT_w (wetting transition temperature), which is different from the case having only one step on a substrate where, as it is well known, step-free energy vanishes at the wetting transition.