SI(111)-(2-ROOT-3X2-ROOT-3)SN RECONSTRUCTION STUDIED BY ION-SCATTERING SPECTROMETRY AND SCANNING TUNNELING MICROSCOPY

The techniques of impact collision ion scattering spectrometry (ICISS) and scanning tunneling microscopy (STM) were used to study the (2 square-root 3 X 2 square-root 3)R30-degrees reconstruction of Sn on the Si(111) surface. Our STM results show that the 2 square-root 3 X 2 square-root 3 structure has three equivalent orientations and that the electronic structure is onefold symmetric. ICISS polar-angle scans, using lithium ions (Li+) backscattered from Sn, establish that Sn atoms are located on top of the Si(111) surface. These scans, which reflect the relative positions of the Sn atoms with respect to each other, are compared with computer simulations of two models of the surface. Reasonable agreement is obtained with a model which contains two layers of Sn atoms.