Department of Chemistry and Laboratory for Surface Studies, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA
Abstract:
The surface chemical activity of an alumina films grown on Mo(100) by oxidation of aluminum evaporated onto the surface and oxidized using water is examined using Auger, X-ray photoelectron and reflection/absorption infrared spectroscopies. The formation of alumina is confirmed using Auger and X-ray photoelectron spectroscopy from the positions and intensities of the aluminum features and using reflection-absorption infrared spectroscopy from the longitudinal optical modes of the Al–O bonds measured at 935 cm−1. The presence of surface hydroxyls is monitored by forming films using D2O which are evidenced by a feature at 2700 cm−1. Ammonia adsorption on a dehydroxylated surface yields a single peak at 1260 cm−1 due to ammonia adsorbed at a surface Lewis site where the principle symmetry axis of ammonia is oriented perpendicularly to the surface plane. Ammonia also appears to adsorb at Lewis sites on a hydroxylated surface with a slightly different adsorption geometry from that on a dehydroxylated surface. Finally, the chemistry of trimethyl aluminum adsorbed on the planar hydroxylated alumina surface is compared with that found on high-surface-area γ-alumina where the spectra and the chemistry found in both régimes is exactly identical except that the low-frequency methyl bending modes (at 769 and 718 cm−1) are not obscured on the thin film by the intense substrate whereas they are on the high-surface-area support.