Chemical vapour deposition -: a new approach to reactive surface defects of uniform geometry on high surface area magnesium oxide

Chemical vapour deposition (CVD) is particularly well suited for the preparation of high surface area magnesium oxide which exhibits a considerably reduced surface heterogeneity. This is shown in the present study for three types of surface defects: low coordinated anions and cations as well as anion vacancies. For each of them, only two to three different species with discrete geometries are observed. The characterization of these defects is based on specific EPR active molecular surface probes, namely, electron deficient oxygen anions O-, superoxide anions O-2(-) and surface colour centres F-S(+), respectively. Some of the O-2(-) and F-S(+) centres exhibit a dipolar magnetic interaction with the proton of a closely spaced OH group. The electronic interaction is reflected by a change of the intramolecular force field of the respective OH group. Consequently, there is an IR spectroscopic access to the characterization of the defects in question. On the other hand, the surface O- species are absolutely insensitive to the hydroxylation state of the MgO surface. (C) 2000 Elsevier Science B.V. All rights reserved.