Surface-structure analysis of Au overlayers on Si by impact-collision ion-scattering spectroscopy: √3×√3 and 6×6 Si(111)/Au

Publisher Website
Google Scholar
Abstract
Amounts of Au equivalent to about 0.8 monolayer and 1.1 monolayers have been deposited onto Si(111) surfaces, and after annealing to 700 °C the atomic structures of the adatom-induced reconstructions (√3×√3 and 6×6, respectively) have been studied using primarily impact-collision ion-scattering spectroscopy (ICISS). The ion-scattering results were quantitatively analyzed by comparing them to the results of computer simulations for various structural models. The scattered-ion angular distributions clearly show that the Au atoms are not embedded in the Si surface, and the underlying Si atoms are not displaced markedly from their bulk positions. Two types of Au adatoms are found on both surfaces: those that are located 2.0±0.2 Å above the outermost Si plane at threefold hollow sites and are arranged in a honeycomb network, and those that reside in the centers of the honeycomb hexagons 0.3±0.05 Å below the honeycomb plane. A model is proposed that is consistent with both the ICISS and low-energy electron-diffraction results: The √3i×√3 surface is essentially an incomplete 6×6 structure with little ordering of the empty honeycomb and centered-hexagon units, whereas the 6×6 surface is predominantly covered by centered hexagons with the empty honeycomb units ordered in a regular array.