Electronic structure of Rb-adsorbed Si(100) surfaces studied with angle-resolved photoemission

Angle-resolved photoemission has been used to study Rb adsorption on Si(100)2x1 at room temperature. The development of the valence-band spectra with increasing Rb coverage and the dispersions of the surface-state bands of the saturated Si(100)2x1-Rb surface are reported. Similar to the adsorption of other alkali-metal atoms on the Si(100) surface a strong surface-state peak appears at the Fermi level in the initial stage of Rb deposition. This surface-state peak is a result of partial occupation of a normally empty surface band. The onset of occupation leads to an abrupt upward shift of the Fermi-level pinning position. For the room-temperature saturation coverage, two surface states were observed in the valence-band spectra with energies of -0.55 and -1.55 eV relative to the Fermi level at normal emission. The dispersions of these two surface-state bands were determined along the [010] azimuthal direction of the two-domain 2x1 reconstructed surface. The surface electronic structures of the different Si(100)2x1-alkali metal (Na, K, Rb, and Cs) surfaces are also compared in the paper.