An infrared spectroscopic investigation of thin alumina films: measurement of acid sites and surface reactivity

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 D 2 O 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 c-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.

Transmission Infrared Spectroscopy of Methyl- and Ethyl-Terminated Silicon(111) Surfaces

“…This absorption energy is expected for a methyl C-H rocking mode, 27 which would be polarized parallel …”

“…This peak was assigned as the C-H symmetric bending, or "umbrella", mode of the methyl group. 22,27 This mode is expected to be normal to the surface if CH 3 replaces Cl on Si(111) as shown in Chart 1.…”

The Surface Chemistry of Propylene, 1-Iodopropane, and 1,3-Diiodopropane on MoAl Alloy Thin Films Formed on Dehydroxylated Alumina

“…Unfortunately, these are obscured by an intense alumina LO mode. 26,27 Following adsorption at 80 K, features at 3072, 3056, 2977, and 2940 cm -1 are found in the C-H stretching region. In the low-frequency region, relatively intense modes are detected at 1645, 1452, and 1435 cm -1 .…”

A novel method for synthesis of nano-γ-Al2O3: study of adsorption behavior of chromium, nickel, cadmium and lead ions

“…All the adsorption bands were at 3,429, 1,829, 1,026, 921, 828 and 515 cm -1 . The strong IR band at 3,429 cm -1 was assigned to the stretching bands of adsorbed water (Kaltchev and Tysoe 1999). The bands around the peak of 1,629 cm -1 were assigned to Lewis sites, and they were also identified on dehydroxylated alumina (Nero et al 2010).…”