Dissolution and segregation of monolayer Cu, Ni and Co atoms on the Si(111)-3×3-Ag surface induced by thermal annealing

Concentration changes of monolayer Cu, Ni, and Co atoms on the Si(111)-3×3-Ag surface by isochronal annealing at temperatures from 150 to 700°C have been studied by means of LEED-AES-RBS techniques. It is shown that Cu atoms on the Si(111)-3×3-Ag surface dissolve into the Si bulk at a temperature of 250°C, and segregate back to the surface when Ag atoms decay from the surface on annealing at temperatures higher than 400°C. It is also shown that Ni atoms, which have once dissolved into the bulk, segregate back to the surface on annealing above 400°C. In the case of the CoSi(111)-3×3-Ag surface, Co atoms preferentially dissolve into the bulk, a situation similar to that of Cu and Ni atoms on the Si(111)-3×3-Ag surface; however, no segregation of Co atoms has been observed upon annealing at higher temperatures. These results are discussed in terms of the heats of mixing between the Ag atoms and the co-adsorbates and also between the co-adsorbates and the Si substrate.