Scanning tunneling microscopy of Sr adsorption on the Si(100)-2×1 surface

The Sr-induced ordered superstructures on the Si(100)-2×1 surface have been studied using ultrahigh vacuum scanning tunneling microscopy and low-energy electron diffraction (LEED) for metal coverages (θ) below one monolayer (ML). At very low coverages (θ≤0.01 ML) Sr atoms adsorb as isolated atoms or small clusters. At submonolayer coverages of ∼θ≥0.12 ML we have observed the alkali-earth metal chains, even at room temperature, that run perpendicular to the substrate dimer rows. It is found that the Sr rows form areas of (2×3) order for coverages θ about 1/3 ML after annealing at 800 °C whereas a (1×3) phase grows on top of this with θ≥1.0 ML coverage in agreement with LEED data. It was also observed that the (2×3) phase formation is critical to the Sr coverage and to the annealing temperature as well. The relationship between the (2×3) and (1×3) ordered structures has been investigated as a function of Sr coverage and annealing temperature.