Interactions of hydrogen molecules with the Si(111) (1 × 1) surface: First-principles calculations

The interactions of hydrogen molecules with the Si(111) (1 × 1) surface have been investigated using a first-principles method. We have calculated the energy curves for H₂ approaching seven distinct sites in the irreducible zone of the Si(111) (1 × 1) surface and considered different orientations of H₂ in each path approaching the surface. The most favoured and disfavoured sites for the hydrogen molecule on the Si(111) (1 × 1) surface correspond to the saddle point (M₂) and the chemisorbed site (T1) of the potential energy surface for atomic hydrogen moving on the surface. The effect of the orientations of the molecule depends strongly on the position of H₂ on the surface and the distance of H₂ from the surface. Several possible dissociative chemisorption processes for H₂ on the surface were studied and, except for the approach path through the M₂ site, all require the overcoming of an energy barrier in the dissociative process. The approach path through the M₂ site was found to be a direct dissociative chemisorption path.