Non-equilibrium Interface and Surface Dynamics

Pattern Formation of a Step Induced by a Guiding Linear Source

Makio Uwaha

Nagoya University

I report on pattern formation of an atomic step induced by a moving linear source of adatoms. A straight step is unstable with the guiding linear source, small projections and dents are formed at the beginning, and a rough step appears. However, the balance between the destabilizing effect of diffusion and the stabilizing effect of stiffness selects a characteristic length. In contrast to usual wandering pattern of a step, a tree-like step follows the source, and a steadily growing state is realized. The branching pattern depends on the crystal anisotropy. A comb-like pattern with few branches may be formed in the <11> directions.

The pattern is similar to that observed on a Si(111) vicinal surface with Ga deposition by Hibino et al.(Surf. Sci. 602 (2008) 2421). If the velocity of the source is increased, the characteristic length is adjusted to follow the source. Above a critical velocity, which is controlled by the fractal dimension of the DLA (diffusion-limited aggregation), the step grows at the critical velocity, independent of the velocity of the source. This kind of pattern formation may be observed in other systems with a moving source of atoms.