Growth of Aluminum Nitride on Porous Alumina and Silica through Separate Saturated Gas−Solid Reactions of Trimethylaluminum and Ammonia

Abstract

Aluminum nitride-type species were prepared on porous alumina and silica by repeated separate, saturated reactions of gaseous trimethylaluminum (TMA) and ammonia with solid substrates. Reaction cycles of TMA at 423 K and ammonia at 823 K were performed up to six times. Growth per cycle was on average 2.4 AlN units/nm2, but it increased slightly with the number of reaction cycles. The amount of hydrogen present in NHx groups increased with the increasing number of reaction cycles. AlN4 units were observed by 27Al NMR on alumina, but the AlN remained amorphous to X-ray diffraction. Scanning electron microscopy combined with energy-dispersive X-ray spectroscopy revealed that the AlN-type species were spread out evenly on the surface of the particles. TMA reacted with equal probability with the still-exposed silica and the AlN-type species present on the surface, as shown by low-energy ion scattering. 29Si and 27Al NMR suggested that transition from the oxide substrates to aluminum nitride occurred through silicon oxynitride for the silica substrate and through aluminum oxynitride for both substrates.