Study of Ga Adsorption Structure on Ni/Si(100) Surface by Scanning Tunneling Microscopy

The Ga adsorption structures on the Ni-induced Si(100) surface have been studied by scanning tunneling microscopy. The protrusions, which are different from Ga ad-dimer, are observed on the dimer vacancy lines (DVLs) after the Ga ad-dimers cover the Si region. The amount of protrusions increases as Ga coverage increases and these protrusions occupy the DVLs at about 0.50 monolayer. The type of protrusions on the DVLs is similar to the precursor state of the Ga clusters. Islands of different sizes are formed locally on the steps and terraces as coverage increases. Small islands are distributed evenly on the terraces after annealing the surface at 200 \mbox{ \circ C}, whereas large islands are formed again at 400 \mbox{ \circ C}. The changes in the distribution of the islands are associated with the nuclei sites on the DVLs and the transformation of the surface structure.