ADSORPTION OF K ON SI(100)2X1 AT ROOM-TEMPERATURE STUDIED WITH PHOTOELECTRON-SPECTROSCOPY

Different coverages of K on the Si(100)2 X 1 surface were studied by photoelectron spectroscopy up to saturation coverage. The K 3p spectra show two components for coverages larger than 50% of saturation, which is consistent with the double-layer model. The Si 2p spectrum at saturation coverage shows a strong, well-resolved, K-induced component, with an energy shift of similar to 0.42 eV, toward lower binding energies. Based on its intensity and the 2 X 1 periodicity observed by low-energy electron diffraction (LEED) this component is assigned to Si atoms forming symmetric dimers on the surface. An abrupt decrease of the band bending at the surface of the n-type sample by similar to 0.23 eV, accompanied by the appearance of a surface state peak at the Fermi level, was observed for the initial growth. This peak is interpreted as due to a partial occupation of an empty surface band existing already for the clean surface. The smeared out appearance of the Si 2p core-level spectra for the smaller K exposures indicates that multiple surface shifts due to an inhomogeneous surface are present. For a coverage of about 30% of the saturation coverage, a sharpening of the line shape of the Si 2p spectra occurred and a 2 X 3 LEED pattern was observed, implying an ordering of the surface. At saturation coverage, another abrupt energy shift of the spectra, by similar to 0.2 eV, occurred toward higher binding energies. This shift. coincides with a metallization of the surface, which has been reported in inverse and direct photoemission studies.