Two-Dimensional Nucleation with Edge and Corner Diffusions

抄録

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∝(F⁄D_s)^1⁄3. At large D_c, dimers and trimers are also mobile and n∝F^3⁄7D_s^−5⁄21D_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.