Two mechanisms forming a comblike step pattern induced by a moving linear adatom source

We carry out phase field simulations to study properties of the comblike step patterns induced by an adatomsource. When an adatom source advances right in front of a step, stepwandering is caused by the asymmetry of thesurface diffusion field and small protrusions are formed. If the velocity of the source Vp is smaller than a criticalvalue V cp , the protrusions follow the adatom source with coarsening of the step pattern, and a regular comblikepattern with finger-like protrusions is formed.With a sufficiently small Vp, the gap of the supersaturation is largeat the adatom source. Since the period of protrusions, , decreases with increasing Vp, the coarsening of steppattern is irrelevant for the protrusions to catch up with the adatom source. Near V cp , the gap of the supersaturationat the adatom source is small. Taking account of the increase in with increasing Vp, the coarsening of the steppattern is essential for the protrusions to follow the adatom source