Electronic structure of α and γ phases of Si(111)––Sn

This work presents a detailed comparison of the electronic properties of two phases (a and y) of the prototypical Si(111)-√3 × √3-Sn system, focussing on the empty surface states. The latter reconstruction has been studied at room temperature with inverse photoemission (KRIPES). For the γ-phase characterised by an equal amount of Sn and Si adatoms, a charge transfer towards the Sn adatom leaves an empty surface state localised on Si adatoms, and observed in KRIPES 0.4 eV above the Fermi level (E F ) at the surface Brillouin zone (SBZ) center. The band gap of this semiconducting γ-phase is estimated around 0.5 eV. In contrast, the a phase with only Sn adatoms shows a metallic behaviour and two distinct adatom-derived empty surface states.