Kinematical binding transition of steps in a surface diffusion field

The motion of steps in a surface diffusion field with asymmetric step kinetics is studied. An effective attraction from interference of the diffusion field causes a kinematical binding transition of two repulsive steps if undersaturation exceeds a critical value. This binding transition leads to a nonlinear growth law, V∼-‖δc${\mathrm{\Vert }}^{2/3}$, for δc<0. If there is a third step at a distance, it collides with the pair and recombination takes place. In a step train this recombination is repeated.