Adsorption of Rb on Si(100)2 × 1 at room temperature studied with photoelectron spectroscopy

Photoelectron spectra of the Si and Rb core-levels have been analyzed for increasing Rb coverage. At the initial stage of adsorption, an abrupt decrease of the band bending at the surface of the n-type sample by ∼0.3 eV was observed, which is due to a partial occupation of an empty surface band existing already for the clean surface. A 2 × 3 low-energy electron diffraction (LEED) pattern was observed for coverages of about 1/3 of the saturation coverage. The Rb 4p and 3d spectra show two components for further Rb adsorption, which provide evidence for two Rb adsorption sites supporting the so-called double-layer model. At saturation coverage, the surface shows a 2 × 1 periodicity in LEED due to the underlying Si dimer reconstruction. In the Si 2p spectra a well resolved structure on the lower binding energy side with an energy shift of ∼0.48 eV is identified as due to Si dimers bonding to the Rb atoms. In the Rb core-level spectra two components, separated by ∼0.55 eV with approximately the same emission intensity, are well resolved in both 4p and 3d core-level spectra. A comparison to other alkali-metal-saturated 2 × 1 surfaces (Na, K and Cs) is also presented.