Characterization of Coadsorbed Molecular Species in a Multilayer Solvent Environment on Insulating Surfaces

By employing metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS, HeI) together with work function measurements and temperature-programmed desorption (TPD), the condensation of multilayer solvent systems, such as water and methanol on ultrathin Mo(100)-supported MgO films, has been investigated. In a first step, the techniques MIES/UPS and TPD are used to characterize the condensation of the pure solvent systems. Data collected in a coverage regime from submono- to multilayers at substrate temperatures between 100 and 500 K are surveyed in order to provide information about the buildup of the multilayer systems on an atomic level. Besides investigating the chemistry of pure phases, the present work provides insight into the chemistry of coadsorbed molecular species in a multilayer solvent environment. It is shown that thin films of amorphous water prepared at 100 K are a good candidate for studying aqueous multilayer chemistry under well-defined conditions, i.e. ultrahigh vacuum, by MIES. We are taking advantage of the unique properties of amorphous water films for investigating the interaction of water with coadsorbates, such as sodium and methanol. A deliberately chosen surface preparation technique in combination with the surface-sensitive electron-spectroscopic technique MIES enables the discrimination of various stages in the complex coadsorbate multilayer solvent reaction. Sodium has been chosen as a representative of a class of highly reactive and readily soluble species, and methanol as a surfactant.