On the Stability of Hydride Configurations on Silicon Cluster Surfaces : A First-Principle Theoretical Study

The Si-H bond energies and wet oxidation of SiH_x (x = 1-3) configurations on silicon cluster surfaces have been studied by ab initio calculations It is found that the Si-H bond energy is simply determined by its local configuration and is about 75.2 to ∼76.3 kcal/mol for silicon monohydride, 77.9 to ∼78 9 kcal/mol for silicon dihydride, and 80.9 to ∼81.6 kcal/mol for silicon trihydride. The evaporation energies of a hydrogen molecule from the dihydride and trihydride configurations are found to be slightly higher than the calculated bond energies However, when a water molecule reacts with them, the reaction energy barriers are found to be generally smaller than 500 kcal/mol, much less than these bond energies. The calculated reaction barriers and heats do not show clear relationships with the bond energies. Rather, the results show that the reaction at SiH₂ is the most unfavorable one whereas the most easy reaction may take place at the Si-Si dimer on a (2 × 1) reconstructed Si(001)-like configuration, Our results indicate that the degradation of hydrogenated silicon nanostructures or bulk silicon surfaces might be significantly determined by the possibility of reaction with water molecules, a hydrogenated surface covered by dihydride configurations being the most inert case.