Density functional theory study of the formation of Si nanostructures on a Si(1 1 1) unreconstructed surface

Density functional theory (DFT) calculations have been used to characterize the bonding geometry in Si nanostructures, such as trimers (Si3), tetramers (Si4) and hexamers (Si6) formed on a Si(1 1 1) surface. Trimers and tetramers were simulated by placing three respectively four Si adatoms in high symmetry adsorption sites on the Si(1 1 1) surface. For Si6 clusters, a combination of these adsorption sites were used. We found that only trimer and tetramer formed by adsorbing Si adatoms in ontop position can be considered as clusters because of bonding interaction among their constituents. For hexamers, bonds are also formed between Si adatoms suggesting their existence as stable entity.