Adsorption of Al atoms on the Si(111) 7 × 7 surface was investigated by STM at room temperature. The adsorbed Al atom displaced a Si center adatom on the surface, and the expelled Si atom diffused inside a half unit cell. The adsorbed Al atom hopped among center adatom sites with a frequency of about 0.01s 1 Introduction Study of atom adsorption and diffusion on the Si surface [1, 2] is of both scientific and technological importance. Information for adsorption site, diffusion path and potential energy barrier is expected from atomically resolved experiments and simulations. On a Si(111) 7 × 7 surface that has the dimer-adatom-stacking fault (DAS) structure, a complex potential energy surface for Si atom adsorption and diffusion exists [3,4]. On the other hand, reconstructed Al adsorbed structure [5] and dynamical adsorption process of the Al atoms [6] were reported for the Si(111) surface. However, the behavior of a single Al atom on the surface is not yet understood. To investigate the adsorption process of the Al atom with three valence electrons on the Si (four valence electrons) surface is of interest from scientific viewpoint because the nature of the Si(111) 7 × 7 surface will be revealed.In this article, we study adsorption and diffusion of Al atoms inside a half unit cell of the Si(111) 7 × 7 surface, especially hopping phenomena of a single Al atom, by using a scanning tunnelling microscope (STM) at room temperature. Adsorption site, atomic exchange with a Si adatom, hopping rate are investigated.
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