Growth and annihilation of nickel silicide studied by scanning tunneling microscopy

Formation of ultra-thin silicides (similar to 1 ML) and its annihilation upon annealing have been studied by scanning tunneling microscopy (STM). Ni clusters adsorb on the Si-7 x 7 DAS structure at room temperature. With increasing substrate temperature, the clusters coalesce to form monolayer silicides. Two kinds of islands, showing root 3 x root 3 and 2 x 2 surface structure, are observed at 400 and 600 degrees C, respectively. Further annealing at higher temperature, Ni diffuses from the surface into the bulk and the surface shows a disordered '1 x 1', and eventually a clean 7 x 7 structure appears with the annihilation of nickel silicides.