|
The adsorption and decomposition of water molecules on silicon surfaces is of interest for both fundamental and technological reasons. From a technological perspective, this interaction is important for the growth of ultra-thin film silicon oxide layers. The relatively uncomplicated H2O molecule allows for a confident identification of surface adsorbate fragments observed in atomic-scale scanning tunneling microscopy (STM) images. It also allows the detailed and accurate calculation of binding energies and reaction barriers using density functional theory (DFT). Here, we present the observation of individual H2O molecules on the silicon (001) surface. We observe the formation of both single- and double-dimer adsorbate structures, the conversion between these two structures, and the formation of new, previously unreported adsorbate configurations. Using DFT, we re-examine the reaction pathways of H2O dissociation on Si(001), considering both inter- and intra-dimer dissociation and diffusion processes. The resultant network of dissociation reactions and rates is analysed using the kinetic Monte Carlo method, which provides a dynamical model of H2O dissociation. We show an excellent level of agreement between our theoretical predictions and experimental observations and present new insights into the nature of this fundamental and technologically important interaction. |