Electronic structure of alpha and gamma phases of Si(111)-root 3 x root 3-Sn

This work presents a detailed comparison of the electronic properties of tw o phases (alpha and gamma) of the prototypical Si(111)- root 3 x root 3-Sn system, focussing on the empty surface states. The latter reconstruction ha s been studied at room temperature with inverse photoemission (KRIPES). For the gamma-phase characterised by an equal amount of Sn and Si adatoms, a c harge transfer towards the Sn adatom leaves an empty surface state localise d 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 semiconduc ting gamma-phase is estimated around 0.5 eV. In contrast, the alpha phase w ith only Sn adatoms shows a metallic behaviour and two distinct adatom-deri ved empty surface states. (C) 2000 Elsevier Science B.V. All rights reserve d.