Role of Si adatoms in the Si(111)-Au(5×2) quasi-one-dimensional system

The unoccupied electronic states of the Si(111)-Au(5×2) system have been studied, using inverse photoemission. Striking similarities exist between the unoccupied bands of the Si(111)-Au(5×2) system and the Si(111)-(7×7) and Si(111)-Au($\sqrt{3}$×$\sqrt{3}$)R30° systems. We argue that these similarities suggest that the Si(111)-Au(5×2) system contains Si adatoms, and that the adatom-induced surface states dominate both the inverse photoemission and photoemission spectra in the vicinity of the Fermi level. If this suggestion is correct, it means that the bands crossing the Fermi level may not be derived from the overlap of Au wave functions. The Au atoms may actually inhibit the formation of a Si adatom-induced band in the direction perpendicular to the Au chains.