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 an nealing of ternary metal (Au, Cu, Ag) adsorbates on the Si(111) surfac e has been studied by means of LEED-AES-RBS techniques. The Ag adsorba te on the Si(111)-root 3 X root 3-(Au, Cu) surface produces a clear 2 root 3 X 2 root 3 LEED pattern on annealing at 300 degrees C. The cove rages for the 2 root 3 X 2 root 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 ar e 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 root 3 X 2 root 3 pattern changes into the root 3 X r oot 3 pattern, which is assigned to the root 3 X root 3-(Au, Ag) struc ture. When the sum of Ag and Cu coverages is less than 1 ML, the Si(11 1)-(Ag, Cu) surface shows a mix of root 3 X root 3 and '' 5 X 5 ''. Th e Si(111)-(Au, Cu) surface shows only a root 3 X root 3 pattern. These results indicate that the Si(111)-2 root 3 X 2 root 3-(Au, Ag, Cu) st ructure is a ternary alloy phase. Since Ag and Cu on the Si(111) surfa ce hardly mix with each other, Au plays an important role in formation of the two-dimensional ternary alloy on the Si(111) surface. (C) 1998 Elsevier Science B.V.