Formation of a Comb–Like Step Pattern on a Vicinal Face

Abstract

  We carry out a phase field simulation to study the formation of a comb–like step pattern induced by a straight adatom source advancing in front of a step. The asymmetry of the suface diffusion field induced by the adatom source causes step wandering and small protrusions are formed. The step pattern is changed by the velocity of the adatom soruce, V_p. When V_p is larger than a critical value V_p^c, the step cannot follow the adatom source. A seaweed-like pattern is formed with small ϵ₄ and a dendritic pattern is formed with large ϵ₄, where ϵ₄ represents the strength of the anisotropy of step stiffness. When V_p < V_p^c, the protrusions follow the adatom source: the comb-like pattern with straight finger-like protrusions, which is induced by step wandering triggered by noise, is formed. For a small V_p, the period of protrusions depends on the strength of noise, but the dependence of the period on the noise strength is week when V_p is near V_p^c. The relation between the period and V_p approaches to that between the width of a channel and the velocity of a needle-like step in the free growth in a channel.