Interaction of Lewis Acids with Si(100)-2x1 and Ge(100)-2x1 Surfaces

In this work we have examined the reactions of Lewis acids (MX3, M = B, Al, or Ga and X = F, Cl, Br, or H) with the Si(100)-2x1 and Ge(100)-2x1 surfaces using Moller-Plesset second-order perturbation theory. After careful consideration of the possible surface reactions, we have determined that all metal-halide Lewis acids react via unactivated dissociative addition reactions where the metal-halide covalent bond is broken. However, two types of final products are seen that depend on the nature of the metal. In the case of aluminum and gallium halides, a weak dative bond between metal and halogen is formed, resulting in the formation of cyclic structures on the silicon and germanium surfaces. This dative bonding is absent in the case of boron, leading to open structures. Our results differ significantly from recently proposed mechanistic models and are comparable to available experimental results.