Atomistic study of the formation process of Ni silicide on the Si(111)-7×7 surface with scanning tunneling microscopy

This paper reports on the surface structure of Ni-induced ‘1×1’ on Si(111) and the dynamical nickel silicide formation observed by scanning tunneling microscopy (STM). The ‘1×1’ surface consists of Si adatoms and two kinds of ring-clusters. The silicon adatoms form the local structure of 2×2 or c(4×2). One of the ring-clusters is found to form the well-known 19×19 structure. The other ring-cluster is observed to be smaller and brighter than the former ones, and forms a local 7×7 arrangement. The latter ring structure has never been reported yet. Islands of nickel silicide are formed after annealing the Ni-covered surface at elevated temperature. The surfaces of the islands show 3×3 and 2×2 periodicity for annealing temperatures of 400°C and 600°C, respectively. The transformation of the island structure seems to proceed through nickel diffusion from the surface into the bulk.