Surface diffusion of adsorbed Si atoms on the Si(111)7x7 surface studied by atom-tracking scanning tunneling microscopy

The initial adsorption process of Si atoms deposited on a Si(111)7x7 surfac e has been investigated at 80 to 500 K using a variable-temperature scannin g tunneling microscopy. At room temperature, adsorbed Si atoms spontaneousl y formed tetramers over the center dimers in the dimers adatoms and stackin g fault model of a 7x7 structure. Many other adsorbed Si atoms, which were not used for the formation of tetramers, were observed to diffuse within ea ch half of the 7x7 unit cell. The diffusion of Si atoms across the surface was examined directly by using an atom-tracking technique. At low temperatu res, 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 ato m beyond the boundary between the half-unit cells was measured as E-a=1.14e V. (C) 2000 American Vacuum Society. [S0734-2101(00)02703-2].