PNNL

Abstract

The structure of an ordered, ultra thin ?-Al203 film grown on a NiAl(100) single crystal surface was studied by Auger electron spectroscopy (AES), X-Ray photoelectron spectroscopy (XPS), and low energy electron diffraction (LEED), and its interaction with water was investigated with temperature programmed desorption (TPD), and XPS. Our results indicate that H2O adsorption on the ?-Al203/NiAl(100) surface is predominantly molecular rather than dissociative. For ?H2O 1ML, H2O overlayers were observed to form three dimensional ice multilayers where water molecules start occupying both cationic and anionic adsorption sites on the oxide surface allowing the formation of hydrogen boding. A small extent of H2O dissociation was observed to occur on the ?-Al203/NiAl(100) surface which was attributed to the presence of a low concentration of surface defects. Titration of these defect sites with absorbed H2O molecules revealed an estimated defect density of ~0.-5 ML for the ?-Al203/NiAl(100) system consistent with the ordered nature of the synthesized oxide film.