Extending molecular lines on the Si(100)-2 × 1 surface: A theoretical study of the effect of allylic mercaptan adsorbates on radical chain reactions

The reaction mechanism for the adsorption and growth of allylic mercaptan (ALM) at a defect site on the Si(100)-2 × 1 surface has recently been proposed. The adsorbate structure is believed to be a branched or linear ALM molecule forming a bridge across silicon dimer rows on the Si(100)-2 ×1 surface. Subsequent reactions at the radical site formed by an ALM adsorbate have not been studied previously. We have now calculated the reactivity of ALM, acetone, and styrene at radical sites formed by an ALM adsorbate. The reactivity of ALM and acetone is unaffected by adjacent ALM adsorbates. The same is true for styrene reacting adjacent to a linear ALM adsorbate. A branched adsorbate significantly destabilizes a styrene adsorbate, making styrene more likely to desorb than to react further. The origin of this destabilization is the partially broken silicon dimer bond. These results are consistent with available experimental observations and support the proposal of a branched ALM adsorbate bridging dimer rows.