Electron correlation, metallization, and Fermi-level pinning at ultrathin K/Si(111) interfaces

In this paper we present a detailed photoemission study of the K/Si(111)7×{}7 and K/Si(111)({}3 ×{} {}3 )R30^∘{}-B interfaces. Angle-resolved valence-band spectroscopy reveals the presence of an almost dispersionless interface state below EF. Both interfaces are clearly nonmetallic at room-temperature saturation coverage. We critically address the issues of charge transfer and Fermi-level pinning by a detailed analysis of the K 3p and Si 2p core-level spectra. We conclude that, up to saturation coverage, correlation effects determine the electronic properties of these interfaces. Metallization occurs during the development of the second layer at cryogenic temperatures.