Submonolayer Growth on a substrate with defect sites using a Level-Set model
R. Vardavas, C. Ratsch , J. Garcia, R.Caflisch
Keywords: Level Set, Defects, Epitaxial Growth, Submonolayer
Submonolayer epitaxy in the presence of point defects is studied by means of a Level-Set method. Here island nucleation occurs by dimer formation and by the atom-defect irreversible attachment. The latter accounts for a new sink term in the evolution of the adatom density proportional to the number of free, non-seeded defect sites. With increasing D/F, the presence of defect sites has the effect that all island nucleation events occur primarily at the defect sites and the formation of dimers is repressed. Furthermore, the time intervals between successive nucleation events are shortened. These observations are in agreement with a rate equation model , where for a particular coverage one obtains an extensive plateau region of constant island density equal to the defect density independently from the ratio D/F.
We further discuss the evolution of the island size distribution for the cases where the allocation of the point defects over the surface is random or uniform. For randomly allocated defects we observe that with increasing D/F, the island size distribution approaches a scaled gamma distribution of the areas associated to Voronoi cells of the defect sites. This distribution differs from that found by Ratsch et al.  for normal growth where dimers are seeded randomly. For uniformly allocated defects and for large D/F the island size distribution becomes very peaked. This suggests that by controlling the positions of the defects we find that the surface morphology can be engineered so that all islands are of similar sizes.
NSTI Nanotech 2003 Conference Technical Program Abstract