Elastic interaction of surface steps: Effect of atomic-scale roughness

Elastic interactions of atomic steps can greatly impact surface morphology. Recent atomistic calculations and experimental observations find the standard dipole model of steps is valid only for very large step separations. In this Letter, a new model is presented that displays remarkable agreement with atomistic predictions for step separations larger than just a few step heights. It is shown that the interaction energy of steps exhibits a novel intermediate-ranged behavior and that, for particular systems, step interactions switch from repulsive to attractive as separation distance decreases.