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).

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.

We investigate the diffusion, nucleation and annealing behaviour of Co on H-passivated Si(100) surfaces by scanning tunneling microscopy (STM). Due to the absence of nucleation sites for silicide formation, the nucleation and growth mode is dominated by the formation of non-epitaxial islands which merge by increasing Co coverage h. The island number density N shows a power law dependence on coverage N3hc (c=0.29±0.03) for room temperature deposition. Annealing at temperatures up to~400°C results in small changes of the Co clusters, while deposition at elevated substrate temperatures (~400°C) results in the formation of fewer but coarser Co islands. Finally, at higher annealing temperatures (~490°C) where H desorption takes place, the formation of twodimensional islands occurs which are surrounded by an irregular 2×n (n>1) reconstructed surface due to interstitial diffusion of Co into Si.