Dissociative adsorption of molecular hydrogen on silicon surfaces

The dissociative adsorption of molecular hydrogen on silicon is considered to be the prototype for an activated chemical reaction at a serniconductor surface. The covalent nature of the silicon-silicon and silicon-hydrogen bonds lead to large lattice distortion in the transition state of the reaction. As a result, the apparently simple reaction exhibits relatively complex pathways and surprisingly rich dynamics. The report reviews, among others, experiments using optical second-harmonic generation, molecular beam techniques and scanning tunnelling rnicroscopy which, in close connection with state-of-the-art density functional theory, have led to a detailed microscopic understanding of H-2 adsorption on Si(001) and Si(111) surfaces. On the dimerized Si(001) surface, dissociative adsorption as well as recombinative desorption of H-2 is shown to involve the dangling bonds of two neighbouring dimers. Preadsorption of atomic hydrogen or thermal excitation is able to substantially alter the adsorption barrier. As a consequence, the reactivity strongly depends oil coverage and surface temperature. In contrast to activated adsorption of hydrogen at metal surfaces, even the most basic description of the dynamics has to include phonon excitation of the silicon substrate. (c) 2006 Elsevier B.V. All rights reserved.