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

Abstract

The Si-H bond energies and wet oxidation of SiHx (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 50.0 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.