Interaction of water with clean and gallium precovered Fe(111) surfaces

The interaction of water with the clean Fe(111) surface and that surface modified by small coverages of Ga has been investigated. Both thermal energy atom scattering and Auger electron spectroscopy have been used to probe this interaction. Water adsorption occurs via a molecular precursor state on these surfaces, and a passivated overlayer is formed on the clean surface exposed to water at 423 K. Small amounts of Ga precoverage, from the decomposition of triethyl gallium, strongly affect the subsequent water adsorption. Preadsorbed gallium reduces the molecular water sticking coefficient and inhibits water dissociation. This effect is proportional to the Ga precoverage. Electron beam irradiation during Auger measurement also strongly affects the water adsorption on the clean and Ga modified surface, and this effect is discussed. (C) 1996 American Vacuum Society.