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 p hotoelectron 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 satu ration coverage shows a strong, well-resolved, K-induced component, wi th an energy shift of similar to 0.42 eV, toward lower binding energie s. Based on its intensity and the 2 X 1 periodicity observed by low-en ergy electron diffraction (LEED) this component is assigned to Si atom s forming symmetric dimers on the surface. An abrupt decrease of the b and 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 le vel, 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-le vel spectra for the smaller K exposures indicates that multiple surfac e shifts due to an inhomogeneous surface are present. For a coverage o f 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 a brupt energy shift of the spectra, by similar to 0.2 eV, occurred towa rd higher binding energies. This shift. coincides with a metallization of the surface, which has been reported in inverse and direct photoem ission studies.