Adsorption of Ag on the Si(1 1 1)√3×√3-Au surface

Thermal properties and atomic arrangements of Ag adsorbates at coverages between 0.1 and 0.8 ML on the Si(1 1 1)√3×√3-Au surface have been studied by means of low energy electron diffraction (LEED), scanning tunneling microscopy, and Rutherford backscattering spectroscopy (RBS). In particular, the two surface structures of 6×6 and 2√3×2√3 are newly observed with LEED. The Ag minimal coverages determined with ex situ RBS measurements are 0.15 and 0.25 ML for the 6×6-(Au,Ag) and 2√3×2√3-(Au,Ag) surfaces, respectively. The Si(1 1 1)6×6-(Au,Ag) surface shows a reversible phase transition between 6×6 at room temperature and 2√3×2√3 at 150°C. STM images for both the 6×6-(Au,Ag) and 2√3×2√3-(Au,Ag) surfaces show p1 symmetry. The 2√3×2√3 periodicity is found additionally in the STM image of the 6×6-(Au,Ag) surface at sample biases lower than 0.5 V. Based on these results, the relationship between the 6×6-(Au,Ag) and 2√3×2√3-(Au,Ag) surfaces is discussed.