Electronic structure of alpha and gamma phases of Si(111)-R3xR3-Sn

This work presents a detailed comparison of the electronic properties of two phases a and g. of the prototypicalSi111.–'3 ='3 –Sn system, focussing on the empty surface states. The latter reconstruction has been studied at roomtemperature with inverse photoemission KRIPES.. For the g-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 0.4eV above the Fermi level EF. at the surface Brillouin zone SBZ. center. The band gap of this semiconducting g-phase isestimated around 0.5 eV. In contrast, the a phase with only Sn adatoms shows a metallic behaviour and two distinctadatom-derived empty surface states.