The structure of different reconstructions of Sn on Si(111) has been studied by scanning tunneling microscopy. For less than a monolayer (ML) of Sn, three reconstructions are seen with 7×7, 7/8 × 7/8 , and 2 7/8 ×2 7/8 periodicities. The 7×7 structure is similar to that of the clean surface. The 7/8 × 7/8 phase is a (1)/(3) ML array of adatoms similar to that of Al, Ga, or In on Si(111). The 2 7/8 ×2 7/8 structure is twofold symmetric with three possible orientations on the surface giving the threefold symmetry apparent in the low‐energy electron diffraction pattern. All three surface phases coexist above 0.3 ML.
We report the use of the techniques of scanning tunneling microscopy and impact-collision ion scattering spectrometry to study the in-plane geometry of both the (root)3X(root)3 and 2(root)3X2(root)3 reconstructions of Sn on Si(111). For the (root)3X(root)3 reconstruction, the Sn adatoms were found to prefer fourfold atop (T4) sites. For the 2(root)3X2(root)3 reconstruction, a two-layer epitaxial Sn model with a four-atom unit cell on the top layer is found to provide the best agreement with experimental data.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero.