Oxygen adsorption on small Si clusters: A full-potential linear-muffin-tin-orbital molecular-dynamics study

Using the full-potential linear-muffin-tin-orbital method, we have performed molecular-dynamics simulations for oxygen adsorption on Si_n (n = 1-7) clusters. It is found that Si₁, Si₂ and Si₃ can react with the O₂ molecule directly to form small SiO₂, Si₂O₂ and Si₃O₂ molecules. For the Si clusters with more than four Si atoms, the O₂ molecule cannot be adsorbed on them directly, due to the potential barrier for dissociative chemisorption of O₂. In contrast, atomic oxygen favours reactions with all the silicon clusters considered here. The formation of strong Si-O bonds makes the structures of the small Si clusters obviously distorted and their stabilities decreased. As for the fragmentation, the processes from Si_nO₂ to Si_n-2 + 2SiO are found to be energetically favourable. The theoretical investigations can help us to understand the existing experimental results.