Atomic layer deposition of zinc oxide on mesoporous zirconia using zinc(II) acetylacetonate and air

The self-terminating chemistry of atomic layer deposition (ALD) ideally enables the growth of homogeneously distributed materials on an atomic scale. This study investigates the ALD of zinc oxide (ZnO) on mesoporous zirconium oxide (ZrO2) using zinc acetylacetonate [Zn(acac)2] and synthetic air in a fixed-bed powder ALD reactor. A broad variety of methods, including thermogravimetry analysis, scanning electron microscopy with energy dispersive X-ray spectroscopy, low energy ion scattering, X-ray absorption near edge structure, X-ray photoelectron spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy-mass spectrometry, and density functional theory calculations were used to analyze the reactant and the resulting samples. The factors affecting the zinc loading (wt%) on ZrO2 were investigated by varying the ALD reaction temperature (160 °C–240 °C), the calcination temperature of zirconium oxide (400 °C–1000 °C) and the ALD cycle number (up to three). The studied process showed self-terminating behavior, with the areal number density of zinc of approximately two atoms per square nanometer per cycle. Zinc was distributed throughout ZrO2. After the Zn(acac)2 reaction, acac ligands were removed using synthetic air at 500 °C. In the following cycles, the already-deposited ZnO acted as nuclei for further ZnO growth. This study demonstrates the potential of Zn(acac)2 as an ALD reactant and provides an initial understanding of ZnO growth via ALD on high surface area porous particles as an example for catalytic applications.