The temperature evolution of ultra-thin films in solid-phase reaction of Co with Si (111) studied by scanning tunneling microscopy

The solid-phase reaction of 5 Å of Co with the Si (111) surface is investigated by scanning tunneling microscopy (STM) in the range from room temperature to 700 °C. Room-temperature deposition leads to a granular film surface. The small grains transform upon annealing between 200 and 300 °C into triangular surface terraces with step heights of 1.5 and 3.1 Å. Further annealing up to 500 °C leads to their growth and a decrease of the relative number of 1.5 Å steps. These observations are explained by the formation of a cobalt silicide with a CsCl-type lattice. Furthermore, apart from the known 2×2 reconstructions and the unreconstructed surface, various surface features like individual double-line-shaped defects and steps with a height of 0.4 Å are resolved. Finally, the formation of pinholes is observed after annealing at 500 °C. They lead upon further annealing to a complicated pinhole-induced CoSi2 network that breaks up into individual islands at ~700 °C