Adsorption of oxygen on Si(100) steps: a study at semiempirical level

In this study oxygen adsorption on steps of the Si(100) surface is investigated with quantum mechanical detail. A cluster model represents the step structure and the oxygen impurity is deposited in this cluster above the dimer rows. A map of the total energy sensed by the adsorbate is constructed by displacing the oxygen atom on the terraces and down the step and allowing the system to relax to the total-energy-optimized configuration by a steepest-descent method. A self-consistent semiempirical molecular orbital method is applied to the evaluation of the total energy. Though the adsorption geometries are reminiscent of the ones observed for the flat surface, the effects of the step geometry are noticeable. They influence both the preferred adsorption sites and the properties of the electronic configuration of the adsorbed system.