The adsorption of Ag on the Si(111) 7×7 surface at room temperature studied by medium energy ion scattering, LEED and AES

We have studied the morphology and reactivity of ultrathin Ag films deposited on the Si(111) 7×7 surface at room temperature, employing the high depth resolution of Medium Energy Ion Scattering. In addition, LEED and AES measurements have been made. For coverages from zero to 5×1014 Ag atoms cm−2 we have observed the formation of a two-dimensional Ag layer, followed by the nucleation and growth of three-dimensional Ag islands for higher coverages (Stranski-Krastanov growth mode). Detailed analysis of the measured peak shapes in the energy spectra shows the presence of very high densities (≈ 1012 cm−2) of islands with height to width ratios less than 0.2. For the coverage range studied (zero to 1 × 1016 Ag atoms cm−2), the number of Si atoms, displaced from lattice sites does not increase above the value for the clean Si(111) 7×7 surface. This shows that no substantial mixing of Ag and Si occurs. The crystallographic relation between the Ag(111) crystallites and the Si substrate has been determined from LEED and Ion Blocking measurements, showing that part of the Ag crystallites have a preferential orientation, 180° rotated around the surface normal, with respect to that of the underlying substrate.