Two-Dimensional Nucleation with Edge and Corner Diffusion

Abstract

The effect of edge and corner diffusions on the morphology and on the density of islands nucleated irreversibly on a flat substrate surface is studied. Without edge and corner diffusion, islands are fractal. As an edge diffusion constant $D_e$ increases, islands tend to take a cross shape with four needles in the $<10>$ direction. Additional corner diffusion with a diffusion constant $D_c$ yields square islands. When $D_e$ is small relative to the surface diffusion constant $D_s$, the square corner shows the Berg instability to produce hopper growth in the $<11>$ direction. The corner diffusion influences the island number density $n$. At a deposition flux $F$ with a small $D_c$, mainly monomers are mobile and $n\propto (F/D_s{)}^{1/3}$. At large $D_c$, dimers and trimers are also mobile and $n\propto F^{3/7}{D}_s^{-5/21}{D}_c^{-4/21}$. The $F$ dependence is in good agreement to the rate equation analysis, but the dependence on $D_c$ cannot be explained by the theory.

8 pages, 7 figures, Change content with additional references and figures