Two-dimensional nucleation with edge and corner diffusions

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-c 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 De 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 proportional to (F/D-s)(1/3). At large D-c, dimers and trimers are also mobile and n proportional to (FD-5/21Dc-4/21)-D-3/7. The F dependence is in good agreement to the rate equation analysis, but the dependence on D-c cannot be explained by the theory.