Step-Bunching Instability of Vicinal Surfaces under Stress

On a vicinal surface under stress, elastic relaxation at steps produces a long-range attractive interaction between the steps. As a result, the surface is unstable against step bunching, driven by the energetics of the system rather than by the kinetics of step flow. This bunching instability differs from the predictions of previous continuum models by its lack of a characteristic wavelength. Instead, it evolves by progressive coalescence of step bunches. Flux can dramatically modify this evolution, limiting the growth of step bunches.