Initial stages of Sn adsorption on Si(111)-(7 x 7)

By means of scanning tunneling microscopy (STM) we have performed a detailed analysis of the initial stages of Sri adsorption on Si(111)-(7 x 7) at room temperature (RT). At very low coverages (Theta approximate to 0.01 ML) single Sit atoms as well as clusters of two Sri atoms can be resolved inside the (7 x 7)-half-cells. According to our STM measurements, single Sn atoms are highly mobile at RT inside the (7 x 7)-half-cells. This thermally activated motion, faster than the scanning speed, results in a characteristic fuzzy appearance of the half-cell. This behavior was first reported for the Pb/Si(111)(7 x 7) system and has since then been observed in the initial stages of growth at RT of other adsorbates on Si(111)(7 x 7) surfaces. For the Sn/Si(111)-(7 x 7) system, by combining real-time STM observations with measurements of cluster size distributions we have been able to gain some insight into the mechanisms involved in the first stages of growth. In particular, the differences observed in relation to the Pb/Si(I 1 1)-(7 x 7) are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.