The ordering of the adsorbed NH₃ molecules across the Si dimer rows on the Si(0 0 1) surface

Scanning tunneling microscopy was used to study the adsorption behaviors of NH₃ molecules across Si dimer rows on a Si(0 0 1)-2 × 1 surface, taking into account the existence of both the on-dimer (OD) and inter-dimer (ID) adsorption configurations. In the OD configuration, the dissociated NH₂ and H form bonds with two Si atoms of a dimer. On the other hand, in the ID configuration, they adsorb at two Si atoms on the same side of two adjacent dimers along the dimer row. The OD configurations on the neighboring dimer rows were preferentially aligned perpendicular to the dimer rows, indicating a strong attractive interaction across the dimer rows, whereas the NH₃ molecules adsorbed in the ID configuration rarely showed ordering behavior.