Very different adsorption path ways of triatomic molecule H₂O on isolated and domains of dangling bonds on the Si(100) surface

On the ideal clean Si(100) surface, dangling bond pairs (DBPs, denoted as -Si-Si-) cover the entire surface. Each dangling bond is an active adsorption site for adsorption of a gas molecule. In this study, isolated DBPs are prepared on a Si(100) surface as well-defined chemically-reactive sites for chemisorption of the prototypical H₂O triatomic molecules. The surrounding dangling bonds are passivated by chlorine-termination. Following saturation exposure to H₂O molecules at room temperature, the adsorbate configurations on these reactive sites as well as on the clean surface have been examined in atomic resolution using scanning tunneling microscopy.

The results show that, while the H-Si-Si-OH adsorbate configuration is common on a DBP, other configurations such as H-Si-O-Si-H and H-Si-Si-H are observed. These findings indicate that a seemingly simple chemisorption reaction on reactive sites involves not only the sites themselves but also the relevant surrounding bonds and adatoms.