Initial adsorption process of Si atoms on an Si(111)7×7 surface studied by scanning tunneling microscopy

Using variable-temperature scanning tunneling microscopy (VT-STM), the initial stage of the Si absorption process on an Si(111)7×7 surface has been investigated at 80 to 500 K. At room temperature, tetramers were formed over the center dimers in the DAS model of the 7×7 structure. However, at low temperatures these tetramers were formed over the corner dimers. It is suggested that the mode of Si absorption process changes depending on the temperature. Many other absorbed Si atoms, which were not used for the tetramer formation, were diffused over an absorption region. The size of the region is strongly related to the sample temperature. The diffusion of Si atoms on the surface was examined using a novel atom-tracking technique.