Thermal reaction processes of ternary metal (Au, Ag, Cu) adsorbates on the Si(111) surface

The change of atomic structures and compositional ratios by thermal annealing of ternary metal (Au, Cu, Ag) adsorbates on the Si(111) surface has been studied by means of LEED-AES-RBS techniques. The Ag adsorbate on the Si(111)single bond√3×√3single bond(Au, Cu) surface produces a clear 2√3× 2√3 LEED pattern on annealing at 300°C. The coverages for the 2√3× 2√3 pattern are in the region of 0.4–0.6 ML for Au, 0.3–0.6 ML for Ag and 0.05–0.25 ML for Cu. The Au atoms are thermally the most stable among the ternary metal adsorbates on the Si(111) surface. When the Cu coverage decreases to 0 ML on isochronal annealing, the 2√3× 2√3 pattern changes into the √3×√3 pattern, which is assigned to the √3×√3single bond(Au, Ag) structure. When the sum of Ag and Cu coverages is less than 1 ML, the Si(111)-(Ag, Cu) surface shows a mix of √3×√3 and “5 × 5”. The Si(111)-(Au, Cu) surface shows only a √3×√3 pattern. These results indicate that the Si(111)single bond2√3× 2√3single bond(Au, Ag, Cu) structure is a ternary alloy phase. Since Ag and Cu on the Si(111) surface hardly mix with each other, Au plays an important role in formation of the two-dimensional ternary alloy on the Si(111) surface.