Atomic-Scale Structure and its Impact on Chemical Properties of Aluminum Oxide Layers Prepared by Atomic Layer Deposition on Silica

We report the atomic-scale structure of alumina layers obtained by atomic layer deposition (ALD) of trimethylaluminium onto partially dehydroxylated silica. Such a detailed insight into the atomic structure of the species formed with increasing Al content was gained using a variety of one- and two-dimensional solid-state nuclear magnetic resonance (NMR) experiments involving ²⁷Al, ¹H and ²⁹Si nuclei. ¹⁵N dynamic nuclear polarization surface-enhanced NMR spectroscopy (¹⁵N DNP SENS) and infrared spectroscopy using ¹⁵N-labelled pyridine as a probe molecule reveal that aluminium oxide layers on amorphous silica contain both strong Bronsted and strong Lewis acid sites, whereby the relative abundance and nature of these sites, and therefore the acidity of the surface, evolve with increasing thickness of the alumina film.