Scanning Tunneling Microscopy and Barrier-Height Study of K-Adsorbed Si(111) 7×7

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Abstract
We have carried out scanning tunneling microscopy and barrier-height (STM-BH) imaging of a K-adsorbed Si(111) 7×7 surface. At small coverages, most K atoms that adsorb at room temperature are observed in the form of K clusters. Contrary to the previous scanning tunneling microscopy (STM) observation by Hashizume et al. [J. Vac. Sci. & Technol. B 9 (1991) 745], isolated K adatoms are rarely found, perhaps because of their high mobility on Si(111) 7×7 at room temperature. In barrier-height (BH) imaging, a significant reduction of -2 ∼-3 eV is observed in the local BH at K sites. The K-induced reduction of BH is larger in the filled state than in the empty state. This polarity dependence of the BH reduction is discussed in terms of the band structure effect in BH.