Ag adatoms on Si(111)5x2-Au surface

Using scanning tunneling microscopy together with the first-principles density functional theory calculations we study structural properties of the Si(111)5x2-Au surface covered by Ag adatoms. The STM topography data show that a submonolayer coverage of Ag does not lead to a well-ordered adatom chain structure with a periodicity 5x4, as it was observed for Si, Pb and In adatoms. Instead of that, we observe Ag adatoms located in different nonequivalent positions within the unit cell, which confirms the electronic nature of stabilization of the Si(111)5x2-Au surface. Moreover, the DFT calculations give five different structural models of the Si(111)5x2-Au/Ag surface. All the models are almost degenerate in energy, which further supports the above scenario.