Adsorption of water vapour on evaporated germanium films. An Infrared Study

Abstract

The interaction of water vapour on evaporated germanium films was studied at room temperature (25°C) by means of infrared spectroscopy. As a result of dissociation of water on the surface, bands were observed at 1980–60, 770 and 675, and at 730 and 875–825 cm^–1. They are attributed to three adsorbed species; the first to Ge–H, the second pair to Ge–OH groups and the third pair to Ge–O^– and oxygen incorporated in the lattice, respectively. Surface oxidation was found to proceed through the elimination of water molecules between neighbouring hydroxyls. From the observed changes in the Ge—H band intensity (while the surface was covered with several layers of physisorbed water) a mechanism is proposed for H₂ formation as a result of the reaction: H_(ads)+ H₂O_(ads)→ OH_(ads)+ H_2(g). An activation energy of ≈ 50 kJ mol^–1 was obtained for this reaction from an Arrhenius plot of the rate of decrease in the Ge—H band intensity at increasing temperatures.