STM/STS investigations of surface evolution of Si(111)-(7x7) induced with nickel

By means of scanning tunneling microscopy and spectroscopy we studied the surface evolution of Si(111)-(7 x 7) induced with nickel followed by annealing at specified temperatures (400, 600, and 800degreesC). Nickel evaporation resulted with 0.05 ML and 0.2 ML coverage was carried out at room temperature with the use of solid phase epitaxy. The characteristic phase formations occurred after gradual annealing the sample depending on the amount of deposited material. At very low coverages scanning tunneling microscopy observation showed two types of ring clusters (1 x 1-RC and clusters of the root19 x root19 reconstruction) accompanied by the Si(111)-(7 x 7) surface reconstruction. All above-mentioned phases appeared in that order as. the annealing temperature increased. Deposition of about 0.2 ML of Ni followed by annealing at 600degreesC formed extended regions of 1 x 1 nickel silicide reconstruction. Very clear, extended regions of root19 x root19 reconstruction appeared when annealed to 800degreesC. The electronic properties of observed structures have been studied by the scanning tunneling spectroscopy. Spectroscopy curves measured above certain surface formations revealed the presence of the Si rest atom, NiSi, and NiSi2 local density of electronic states.