Thermal evolution of the morphology of Ni/Ag/Si(111)-√3 × √3 surface

The temperature-driven changes in morphology of the interface formed by room temperature (RT) deposition of Ni atoms onto an Ag/Si(111)-√3 × √3 surface were investigated by scanning tunneling microscopy. Roughly 70% of Ni deposition diffused into bulk substrate within the temperature range between RT and 573 K. The images as obtained after annealing up to 670 K correspond to the formation of nano-sized islands of nickel silicides. Two types of islands, large triangular islands typical of the whole range of applied coverage, and smaller islands of different shapes, coexist at Ni coverage higher than 1 monolayer. Annealing above 870 K led to the formation of a 7 × 7 phase in coexistence with small 5 × 5 domains at the expense of a complete disappearance of the √3 × √3 phase. Also, formation of Ni,Si alloy was observed at the temperature, along with segregation of bulk-dissolved Ni species onto the surface.