We have fabricated nanometer width Co/Si metal lines on Si(100) surfaces by ultrahigh-vacuum scanning tunneling microscopy (UHVSTM) based nanolithography on the hydrogen-passivated surface, combined with vapor deposition of Co at room temperature and subsequent annealing. The STM tip was used to define depassivated lines (<10 nm in width) by electron stimulated hydrogen desorption, and subsequently Co was deposited at a submonolayer coverage. Annealing of the substrate at 410 °C (just below hydrogen desorption) improves the structure of the wire due to silicidation, whereas the as-deposited wire is very granular (comparable to other materials in previous studies).

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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 CoSi 2 network that breaks up into individual islands at~700°C.