Theoretical investigation of molecule adsorption and dissociation mechanisms on the silicon surface

We have found that mult-dime silicon cluster models can provide ClCN dissociation pathways that are more feasible than the one from using the single-dimer silicon cluster model. The resulting multi-dimer reaction pathways, unlike the previous single-dimer pathway, are consistent with the experimental observations.;The calculated dissociation pathway of benzene on the Si(100) surface revealed that spin crossing from a single to a triplet state is required. The calculated high energy barrier explains why benzene does not dissociate on the Si(100) surface, consistent with experimental results, but in contrast to some recent theoretical results. It is also found that the adsorption and dissociation of phenanthrene molecule on Si(100) surface is analogous to the benzene molecule, except additional geometrical selection rules are observed for phenanthrene adsorption.;Several ab-inito theories and DFT have been used to calculate the energy separation and the spin crossing probability between the singlet and triplet state of Si(100) surface. It is found that the spin crossing process barrier for the bare silicon dimer cluster is moderate, and thermodynamic equilibrium between the singlet ground state and the triple excited state of the silicon dimer cluster can be established at room temperature. Non-negligible population of triplet silicon dimer cluster will present at the Si(100) surface at high temperature.;Finally, we have tested the application of a quantum capping potential (QCP) method on building the silicon dimer cluster. Using single-dimer cluster, the QCP method has shown promising results for the hydrogen terminated cluster model. However, for the bare cluster model, it has failed on reproduction the electronic property of larger size silicon dimer cluster models.