Initial stages of Mg adsorption on the Si(111)-7x7 surface

First-principles calculations are performed to determine the configurations of adsorbed Mg atoms on the Si(111)-7x7 surface. It is shown that Mg atoms prefer to occupy the higher coordination sites of the faulted half unit cell and that they may diffuse laterally to the nearby ones around the same Si center adatom by overcoming a low diffusion barrier of 0.1325 eV. These characteristics are attributed to weak interactions among Mg and nearby Si atoms. The initial adsorption processes of Mg atoms on the Si(111)-7x7 surface are investigated by scanning tunneling microscopy imaging at room temperature. Three types of adsorption sites are identified, which, by comparing with theoretical simulations, are found to be associated with the adsorbed configurations of one, two, and three Mg atoms, respectively.