Density-functional theory was used to investigate the properties of (111), (100), (110) and stepped (111) surfaces with regard to the formation energies of surfaces, steps, adatoms and vacancies. It was found that, for the adsorption and diffusion of Al on flat regions of (111), the hexagonal close-packed site was energetically slightly preferable to the face-centered cubic site. The energy barrier for self-diffusion on (111) was very low (0.04eV). When close to either of the 2 types of close-packed mono-atomic step on (111), Al adatoms experienced an indirect attraction of up to 0.1eV to the edge of the step. This had a range of several atomic spacings, and was electronic in origin. At the lower step edge, an adatom could attach, with no barrier, at a low-energy 5-fold coordinated site. When coming from the upper terrace, it was incorporated into the step via an atomic exchange whose barrier height was less than 0.1eV for both types of close-packed step. The barrier to diffusion along the lower edge was 0.32eV at the {100}-faceted step, and 0.39eV at the {111}-faceted step. The latter diffusion process occurred via an exchange mechanism. Diffusion via an exchange mechanism was also found for the so-called easy direction on (110); that is, along channels. It was shown that (110) was a model system for diffusion at the {111}-faceted step on (111) because of its similar local geometry. Estimates were made of the temperature ranges for various modes of homo-epitaxial growth on (111). Particularly important were the relatively low barriers for diffusion across the descending steps, and the relatively high barriers for diffusion along the steps. It was noted that, depending upon the temperature, the island growth shapes on (111) could be fractal, triangular or hexagonal, and were determined mainly by kinetics. Under equilibrium conditions, the island shape was hexagonal and was determined by the various step formation energies.

R.Stumpf, M.Scheffler: Physical Review B, 1996, 53[8], 4958-73