STM study of Sr adsorption on Si(100) surface

Reconstructed structures of strontium (Sr) on the Si(100)-2 × 1 surface annéaled at high temperature have been investigated using ultra-high vacuum scanning tunneling microscopy (STM) 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 13 ML after annealing at 800°C whereas a (1 × 3) phase grows on top of this with θ ≥ 1.0 ML coverage in good agreement with our 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.