Progress into Understanding of Alkali Metal Interaction with a Silicon Surface
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The atomic and electronic structure and interface formation of alkali metal (Na, K, Rb, Cs) and Si(100)2 × 1 surfaces is investigated by photoemission - XPS, UPS - using synchrotron radiation, scanning tunneling microscopy (STM) and by photoemission extended X-ray absorption fine structure (PEXAFS) experiments. The XPS-UPS results indicate that the alkali metal-silicon bond is a weak and polarized covalent bonding even at low coverages with adsorbate metallization at the monolayer. In contrast to III-V semiconductor surfaces, alkali metals do not induce significant structural changes of the surface: STM images performed with atomic resolution for the representative K/Si(100)2×1 systems demonstrate that, at one mono-layer coverage, the K atoms form one-dimensional linear metallic chains parallel to the Si dimers rows ⟨110⟩ direction and distant by 7.68 Å with a single site of adsorption. Below half a monolayer, the K atoms occupy various coexisting sites with no long range order. An ordering transition occurs around half a monolayer in which the adsorbate-adsorbate interaction, which was so far neglected in theoretical calculations, appears to be the leading driving force. The proposed models and concepts are discussed and compared to the latest state-of-art theoretical calculations.
- Commissariat à l'Energie Atomique, Service de Recherche sur les Surfaces et l'Irradiation de la Matière, Centre d'Etudes de Saclay, 91191 Gif sur Yvette Cedex, France
- Département de Physique, Université de Paris-Sud, 91405 Orsay Cedex, France
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