Formation of Ni-driven nano-sized structures on Ag/Ge(111)-3 × 3 surface: STM study

The formation of nano-sized structures upon room temperature (RT) deposition of small amounts of Ni (∼0.1 ml) onto an Ag/Ge(111)-3 × 3 surface was investigated by scanning tunnelling microscopy. The RT behaviour was dominated by the formation of Ni clusters, which did not interact chemically with the surface. The images as obtained after annealing within the temperature range between 100°C and 500°C corresponded to the formation of clusters as well as triangular, elongated and hexagonal-shaped nano-sized islands. Annealing above 550°C resulted in the transformation of the 3 × 3 phase into a c(2 × 8) phase. This process was accompanied by the thermal decomposition of the majority of the islands, except the hexagonal-shaped ones. The latter remained on the surface in an unaltered form upon annealing even at 800°C. We propose that the hexagonal-islands are made of Ni and Ge compounds rather than pure Ni atoms.