TIN-INDUCED RECONSTRUCTIONS OF THE SI(100) SURFACE

The behavior of tin on the Si(100) 2 X 1 surface has been studied using scanning tunneling microscopy. At room temperatures (T < 150-degrees-C), low coverages of Sn form dimer rows that are oriented perpendicular to the underlying Si dimer rows. As the coverage is increased, these rows pack into areas of two-dimensional order, forming small regions of 2 X 2 near 0.5 monolayer (ML). For substrates annealed above 500-degrees-C, the following reconstructions are known to occur: c(4 X 4) and 2 X 6 below 0.5 ML, c(4 X 8) for 0.5-1.0 ML, and 1 X 5 for 1.0-1.5 ML. A number of structures are observed by scanning tunneling microscopy which are associated with these reconstructions. Both the c(4 X 4) and 2 X 6 phases consist of missing Si dimer trenches and stripelike structures which grow perpendicular to the Si dimer rows. As the coverage is increased, the c(4 X 8) reconstruction occurs when chainlike structures, consisting of buckled Sn dimers, form on the surface between trenches. The 1 X 5 phase then grows over this c(4 X 8) layer and consists of bright features which are probably associated with Sn dimers. When more than 2 ML Sn is deposited and annealed, the surface undergoes a gross rearrangement and forms {311} facets.