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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., 8 pages, 2 figures

The influence of charged STM tip on the electron transport through quantum states on a surface is studied both theoretically and experimentally. The current and the differential conductance calculations are carried out by means of the Green's function technique and a tight-binding Hamiltonian. It is shown that sharp STM tip is extra occupied and this additional charge breaks the conductance symmetry for positive and negative STM voltages. The experiment on Ag islands with two STM tips (blunt and sharp) confirms our theoretical calculations., Comment: 26 pages, 12 figures

The electrical conductivity changes of the Si(111)-(6x6)Au surface at early stage of Pb deposition was studied experimentally and theoretically as a function of coverage. Pb deposition onto a Si(111)-(6x6)Au surface induce strong change of the conductance even at a low coverage ($, 8 pages, 4 figures