THERMAL-STABILITY OF 2-DIMENSIONAL ATOMIC STRUCTURES OF AU-AG ADSORBATES ON SI(111) SURFACES

Isochronal annealing of Au-Ag binary adsorbates at the Si(111) surface at temperatures from 200 to 430-degrees-C has been studied by means of low energy electron diffraction, Auger electron spectroscopy, and Rutherford backscattering spectroscopy techniques. It was found that a square-root 3 X square-root 3-(Au, Ag) structure was formed by annealing for 15 min at 200-degrees-C Ag atoms on the Si(111)-5 X 1-Au surface at Au coverages less than 0.60 ML, and that the square-root 3 X square-root 3 structure was kept until Ag decreases from 0.70 ML down to 0.18 ML due to the annealing, while the initial Au coverage was kept. Furthermore, when the Ag atoms, which are more than 0.60 ML, on the Si(111)-square-root 3 X square-root 3-Au surface were annealed at 200-degrees-C, a new structure of 2 square-root 3 X 2 square-root 3-(Au, Ag) was observed. Then, the square-root 21 X square-root 21R(+/- 10.89-degrees)-(Au, Ag) structure was formed by prolonged isochronal annealing and was kept until Ag decreases down to 0.12 ML, while the initial Au coverage was kept. From analysis of the decay curves of Ag coverage, it was determined that the activation energies for Ag atoms on Si(111)-5 X 1-Au and Si(111)-square-root 3 x square-root 3-Au surfaces to be dissolved into the bulk were 0.61 +/- 0.15 and 0.52 +/- 0.15 eV, respectively.