INITIAL-STAGES OF METAL-SEMICONDUCTOR INTERFACE FORMATION - AU AND AG ON SI(111)

We have studied the atomic structures formed by monolayer coverages of Au and Ag on the Si(111) surface using primarily the technique of impact-collision ion scattering spectroscopy (ICISS). For the case of Au films annealed at 700°C, three different types of LEED patterns are formed depending on the fractional monolayer coverage: 5 × 1, √3 × √3, and 6×6. The ICISS data reveal that all the three surfaces are structurally similar: the Au atoms reside above the Si(111) plane, most likely in threefold-hollow sites, and the different surfaces appear to be characterized by rows (5×1) or a honeycomb network (√3×√3 and 6×6). In contrast, the Ag films deposited at elevated substrate temperature (480°C) display only a √3×√3 LEED pattern for coverages ranging from 0.25 to 35 monolayers. A trimer model appears to be more consistent with the low coverage Ag ICISS data rather than a honeycomb arrangement of the Ag atoms. © 1989.