Surface diffusion of adsorbed Si atoms on the Si(111)7×7 surface studied by atom-tracking scanning tunneling microscopy

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Abstract
The initial adsorption process of Si atoms deposited on a Si(111)7×7 surface has been investigated at 80 to 500 K using a variable-temperature scanning tunneling microscopy. At room temperature, adsorbed Si atoms spontaneously formed tetramers over the center dimers in the dimers adatoms and stacking fault model of a 7×7 structure. Many other adsorbed Si atoms, which were not used for the formation of tetramers, were observed to diffuse within each half of the 7×7 unit cell. The diffusion of Si atoms across the surface was examined directly by using an atom-tracking technique. At low temperatures, the adsorption position of the Si atom was found to depend only on the potential energy. At high temperatures, the activation energy of an Si atom beyond the boundary between the half-unit cells was measured as Ea=1.14 eV.