Studies on the nucleation, dynamics and structure of the Si(1 1 1)–3×3-Ag surface using surface second-harmonic generation

We have used surface second-harmonic generation (SHG) to study the dynamics of surface processes during the adsorption of silver at room temperature as well as the formation of the Si(1 1 1)–3×3-Ag surface at elevated temperatures on Si(1 1 1)-7×7 surface. Further, the temperature and the flux dependence of the nucleation of the Si(1 1 1)–3×3-Ag phase is also studied. The SHG intensity is found to depend on the density of the two-dimensional adatom gas on the 3×3-Ag surface as a function of temperature and silver flux. The results from the experiments slightly differ depending on the probe wavelength and this has been attributed to the different origins of the SH at the two wavelengths studied here. The polarization sensitivity of SHG to the surface symmetry is used to infer structural changes on the surface. The temperature dependence of the ratio of the SH intensity in the vertical and horizontal polarization directions (extinction ratio) is related to the surface symmetry and its change is interpreted mostly by the variation of the time dependence of the fluctuation in the 3×3-Ag structure. The possibility of finding the structural phase transformation is also discussed.