Abstract:Auger electron spectroscopy, low-energy electron diffraction, and differential reflectometry in the photon energy range 1.5–4.5 eV have been used to study the room-temperature adsorption of O2 on the Si(110) surface with an initial 5×1 superstructure. The reaction kinetics are complicated. Five adsorption stages can be discerned, the first stage (0–2 L) being remarkably fast with an initial sticking probability near unity. Our results suggest that the surface sites which constitute the higher-order reconstructions and possibly also defects, are highly reactive. In the second stage (2–200 L) the O2 adsorption can be described by a dissociative process on the first-layer Si atoms, the sticking probability being about 2×10–3. Incorporation of oxygen into the subsurface Si lattice and possibly also adsorption of a molecular oxygen species are the main processes of the third stage (200–1000 L). In the fourth stage (103–4×104 L) O2 adsorption completely removes the dangling bonds. This occurs at 0.79±0.15 monolayer oxygen coverage. The number of dangling bonds per 5×1 unit cell (ten atoms) is thus eight or less. The fifth stage (>4×104 L) comprises a slow further oxygen adsorption with a sticking probability of ~10–6: oxygen mainly goes into a bridging position between two first-layer Si atoms in the uppermost chains of the ideal (110) surface. The optical spectrum indicates that the clean Si(110) surface probably has several types of (dangling bond) surface states.