Temperature dependent interactions of water vapor with a beryllium surface

Abstract

The temperature dependence of the dissociation of H 2O, adsorption of its products on a Be surface and the initial oxidation process were studied. In contrast to the room temperature one-step full dissociation, at 150 K the dissociation is into H and OH, the latter being adsorbed on the surface. Above a certain dose, adsorption of an ice layer occurs. Heating such an adsorbed ice layer to 200 K, causes some of it to desorb, leaving adsorbed hydroxyls on the surface. Further warming causes complete dissociation of the hydroxyls and oxidation of the surface. At 375 K the whole surface is transformed into an oxide. Exposing an O 2 pre-oxidized Be surface to residual H 2O for a long period, yields hydroxyl adsorption on the oxide. A time dependent mechanism of electron supply by tunneling through the oxide layer, causing the partial dissociation of the water molecules, or attachment to the surface of hydroxyl groups, is suggested.