Thermal step bunching on the restricted solid-on-solid model with point contact inter-step attractions

We present the restricted solid-on-solid (RSOS) model with the inter-ledge interaction of the point contact type (p-RSOS model). We have made detailed calculation of the Andreev free energy f˜(ηx,ηy), which is similar to the equilibrium crystal shape (ECS) z=z(x,y), and the surface gradient p→=(px,py)=(∂z/∂x,∂z/∂y) as the function of the Andreev field η→. From the calculated f˜(ηx,ηy) and p→(η→), we have obtained the vicinal surface free energy f(p→). The inter-ledge attraction between adjacent steps affects the surface free energies in the equilibrium, and causes the first-order transition on the profile of ECS at low temperature. The inter-ledge attraction also destabilizes the regular train of steps. We also have obtained the thermal step bunching.