Attractive interactions between like-oriented surface steps from an ab initio perspective: Role of the elastic and electrostatic contributions

At low temperatures the interactions between like-oriented steps on a surface are believed to be dominated by elastic repulsions. This belief is based on the results of the classical continuum field theories of elasticity. Electrostatic interactions are also believed to have a role but no theory has yet been developed for their description. In our paper we critically revisit the assumptions of these theories, and found that the ab initio approaches, based on the Born-Oppenheimer distinction between the valence electrons and the ions degrees of freedom, allow to identify distinctly both elastic and electrostatic contributions to the step energy and the step interaction energy. By using ab-initio calculations and specifying to the case of the technologically important (001)surface of GaAs, we show that the elastic interactions are not always repulsive and attractive step interactions between like-oriented steps are also possible. Furthermore, the repulsiveness and attractiveness of the step interactions depend on the step atomic structure.