Phonon-assisted sticking of molecular hydrogen on Si(111)-(7 x 7).

Abstract

The initial sticking probability for dissociative adsorption of molecular hydrogen on Si(111)- $(7\ifmmode\times\else\texttimes\fi{}7)$ was measured as a function of substrate temperature. By monitoring the hydrogen coverage of the surface in an ${\mathrm{H}}_{2}$ atmosphere with optical second-harmonic generation we find a sticking coefficient that increases from $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ at $580\mathrm{K}$ to $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ at $1050\mathrm{K}$. An effective barrier to dissociative adsorption of $0.87\ifmmode\pm\else\textpm\fi{}0.1\mathrm{eV}$ via a substrate-phonon-assisted process is deduced. The results reveal a new type of adsorption dynamics where the lattice distortions play a major role.