Atomic structure, adsorbate ordering, and mode of growth of the K/Si(100)2×1 surface

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Abstract
We present an investigation of the structural properties, atomic structure, adsorbate mode of growth, and interface formation of the room-temperature K/Si(100)2×1 system by a combination of core-level and valence-band photoemission spectroscopies using synchrotron-radiation and scanning-tunneling-microscopy experiments. The results indicate that, at saturation coverage, the potassium atoms appear to form one-dimensional chains parallel to the silicon dimer rows along the 〈110〉 direction 7.68 Å apart with a single site of adsorption. These K chains pass over the surface step edges to be connected between themselves. The growth and occurrence of a second layer are clearly related to the presence of impurities which, even at very low levels, are shown to significantly increase the K sticking coefficient. It demonstrates the extreme sensitivity of this system and stresses the crucial importance of quality in surface preparation and alkali-metal deposition. At a lower coverage, the K atoms are adsorbed on various coexisting sites with no long-range order. An ordering transition leading to the formation of the one-dimensional linear K metallic chains occurs. The adsorbate-adsorbate interaction is the dominant driving force in this adsorbate-ordering transition. The valence-band results indicate that the K atoms are covalently bonded to the Si atoms through the dangling bond, which makes the cave the most favorable adsorption site for the K atoms. This investigation brings new insights into the understanding of the structural properties of (alkali metal)/Si(100)2×1 systems.