Contrasted electronic properties of Sn-adatom-based (root 3X root 3)R30 degrees reconstructions on Si(111) - art. no. 115407

We have investigated the electronic structure of the two-dimensional solid solution SixSn1-x/Si(111)-(root3 x root3)R30 degrees at room temperature, w ith a particular emphasis on the empty states, using both global [k(//)-res olved inverse photoemission spectroscopy (KRIPES)] and local probes (scanni ng tunneling microscopy and spectroscopy, STM and STS), as well as DFT-LDA calculations. This adatom overlayer with a (root3 x root3)R30 degrees symme try shows drastic evolution with increasing Sn-adatom concentration, includ ing a semiconductor to metal transition. The Si0.5Sn0.5/Si(111)-root3 or mo saic phase has a single empty surface state localized at 0.56 eV above E-F at Gamma. With an overall bandwidth of approximate to0.15 eV, this sp(z)-ty pe state localized on Si adatoms does not cross E-F: the mosaic phase is se miconducting, with a bandgap between 0.3 and 0.5 eV. This phase is characte rized by a large corrugation of 0.75 Angstrom with Sn adatoms higher than S i adatoms. In the Sn-rich limit SixSn1-x/Si(111)-root3 with x less than or equal to0.05, we follow an empty state U-1' throughout most of the surface Brillouin zone except near the (K) over bar point where it clearly crosses the Fermi level. A second, empty surface state U-2' is detected 1.67 eV abo ve E-F. Once correlation effects suggested by the small bandwidth of U-1' a re adequately taken into account, we explain our KRIPES results in the fram ework of a dynamical fluctuations model as originating from an underlying ( 3 x 3) structure. Finally, results pertaining to intermediate Sn-adatom con centrations are interpreted in view of the two limiting cases.