Highly site-specific H-2 adsorption on vicinal Si(001) surfaces

Experimental and theoretical results for the dissociative adsorption of H-2 On vicinal Si(001) surfaces are presented. Using optical second-harmonic g eneration, sticking probabilities at the step sites are found to exceed tho se on the terraces by up to 6 orders of magnitude. Density functional theor y calculations indicate the presence of direct adsorption pathways for mono hydride formation but with a dramatically lowered barrier for step adsorpti on due to an efficient rehybridization of dangling orbitals.