Iodine Adsorption on Arrays, Clusters, and Pairs of Reactive Sites on the Si(100) Surface

Isolated, paired, and clustered dangling bonds are prepared on a Si(100) surface as well-defined chemically reactive sites for chemisorption of iodine diatomic molecules. The surrounding dangling bonds around a designed reactant configuration are passivated by hydrogen- and iodine-termination. Following exposure to I-2 at room temperature, the adsorbate configurations on these reactive sites have been examined using scanning tunneling microscopy (STM). On clean Si(100), three types (type-I, type-II, and type-M) of adsorption pathways have been identified, consistent with previous findings. The results from H- and I-masked Si(100) show that at least two dangling bonds in the same row and in close proximity (<4 angstrom) are needed to trigger chemisorption and that dissociative adsorption is the dominant mechanism. Contrary to its major role on clean Si(100), type-II adsorption is not observed when the two needed dangling bonds are surrounded by H-adatoms. 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.