Electronic properties of the annealed interface between Ag and 7 × 7 Si(111)

Photoemission yield spectroscopy measurements, associated with LEED and Auger characterisation, are performed on a set of silicon (111) surfaces with different bulk dopings as a function of silver coverage theta , from zero to a few monolayers, obtained by UHV evaporation on a sample kept at room temperature then annealed at 500 degrees C. When the square root 3 × square root 3 structure which is completed theta c approximately=2/3 monolayer is substituted for the 7 × 7 LEED pattern the work function of the system does not vary significantly, while the ionisation energy decreases by about 0.5 eV; it corresponds to a band-bending variation in the Si space-charge region that is in agreement with the change of surface-state density in the gap. The persistence of a Si dangling-bond peak after completion of the first silver layer favours models where a two-dimensional ordered layer is formed allowing Si atoms to be at the surface.