Surface electronic structure at Si(100)-(2x1)

The surface electronic structure of the clean Si(100)-(2x1) surface at room temperature is studied by high-resolution electron-energy-loss spectroscopy. Main absorption edge is detected at similar to 0.4 eV, which corresponds to the energy gap of the system, further structures are singled out at 0.8 and 1.25 eV and ascribed to interband electronic transitions between dimer-related levels. The paramount importance of cleanness is addressed showing and quantifying the effect of the residual gas atmosphere (that can be present in ultrahigh vacuum) on the electronic structure.