Morphological instability caused by asymmetry in step kinetics

We study motion of a train of linear repulsive steps in a surface diffusion field. With asymmetric step kinetics (Schwoebel effect) and repulsive step interaction, fluctuations of step density at long wavelengths become unstable if undersaturation exceeds a critical value. This leads to a morphological instability, in which the diffusion takes place along the interface in contrast to the usual Mullins-Sekerka instability. The instability develops a step bunch with a diffuse front and a sharp end.