STRUCTURAL STUDIES OF THE MG/SI(111) INTERFACE FORMATION

Structural aspects of the formation of the Mg/Si(111) interface at room temperature were investigated by surface EXAFS at the Mg K threshold. Bond lengths and the symmetry of the adsorption sites were determined as a function of Mg coverage. The Mg atoms are found to adsorb on fourfold sites above second-layer Si atoms (T4)it, with bond distances to first- and second-layer Si atoms equal to 2.60 ± 0.04 Å and 2.47 ± 0.04 Å, respectively. While in the initial stage of adsorption, no adsorbate-induced LEED pattern is observed, the Mg atoms on T4it positions give rise to a (√3 × √3)R30° superstructure at a coverage of 1 3 ML. Further Mg deposition preserves the LEED pattern, while the polarization-dependent SEXAFS spectra reflect the presence of additional Mg atoms at off-centered T sites midway between two Mg atoms at T4it sites. At coverages above 1 ML Mg, the LEED pattern disappears, and a contraction of the Mg-Mg bond distance to the bulk value is found. © 1990.