Step wandering due to the gap in diffusion coefficient on the upper and the lower terraces

In a vicinal face of a crystal, wandering instability of steps may occur under nonequilibrium conditions when asymmetry in the surface diffusion field exists. Near the transition temperature of Si(1 1 1) surface between 1×1 and 7×7 structures, wandering instability is observed in growth. We provisionally attribute this instability to the gap in diffusion coefficient on the upper and the lower terraces whose surface structures are different. With linear stability analysis and Monte Carlo simulation, we show that the instability occurs in growth if the diffusion coefficient of the lower terrace is larger. The wandering pattern in a vicinal face is chaotic when evaporation is allowed, but is rather periodic when evaporation is absent. The latter result agrees with the experimental observation.