The role of repulsive interactions in molecular bromine adsorption and patterning of Si(100)-2×1

Scanning tunneling microscopy (STM) was used to investigate the role of repulsive interactions in the adsorption and patterning of molecular bromine on the Si(100) surface. At room temperature and low coverage, chemisorption of bromine occurs dissociatively on the same side of adjacent dimers of the same row. Using the STM tip as a probe, we demonstrate the existence of repulsive interactions at adjacent sites on the Si(100)-2×1 surface. These repulsive interactions also contribute to the arrangement of adatoms on the surface. In particular, we report the presence of a stable c(4×2) surface phase that results after exposing the Si(100) surface to bromine under certain conditions. This phase involves adsorption on non-neighboring dimers and is stabilized by repulsive interactions that force bromine adatoms to occupy alternating dimers within rows with an out-of-phase occupancy between adjacent rows.