AVS 45th International Symposium
    Surface Science Division Friday Sessions
       Session SS2-FrM

Paper SS2-FrM6
Surface Restructuring of Magnesium Oxide at the Interface with Water

Friday, November 6, 1998, 10:00 am, Room 309

Session: Water and Ice Interfaces
Presenter: J. Jupille, CNRS, France
Authors: J. Jupille, CNRS, France
P. Nael, Laboratoire CNRS/Saint-Gobain, France
D. Abriou, Laboratoire CNRS/Saint-Gobain, France
H. Arribart, Saint-Gobain Recherche, France
Correspondent: Click to Email
Interactions of water with oxide surfaces are among the most common chemical reactions since they can be observed at any time in the surrounding medium. Nevertheless, despite their apparent simplicity, they often lack microscopic description. A well known example is the adsorption of water on magnesium oxide. Cleaved MgO samples, which show mostly flat (100) terraces, undergo dramatic rearrangements upon exposures to surrounding atmosphere. Their surfaces are becoming very rough, so that flat (100) terraces are no longer visible. These changes in morphology are usually suspected to arise from the reaction with water molecules present in the ambient air. However, according to theory, water is not expected to dissociate on the dense (100) faces of MgO, but only on sites of lower coordination numbers. To demonstrate that water adsorption induces a restructuring of the MgO(100) surfaces, the behaviour of cleaved MgO surfaces which have been brought in contact with water have been examined by atomic force microscopy. It has been observed that pits are formed along <110> directions. Moreover, rearrangements along similar directions have been seen by exposing cleaved MgO surfaces either to the ambient air or to moist nitrogen. Consistently with calculations relative to hydroxylated MgO surfaces, the orientation of the pits suggests that the driving force for the restructuring is the change in surface energy upon water adsorption.