Investigation of the Hydrophobic Nature of Metal Oxide Surfaces Created by Atomic Layer Deposition

Surface hydrophobicity can be exploited in the design of catalyst materials to improve their activity and selectivity. One versatile method for modifying the hydrophobicity of the environment surrounding an active site is atomic layer deposition (ALD). In this work, Al2O3, TiO2, and SiO2 deposited by ALD as well as CeO2 deposited by electron beam evaporation-all on alpha-Al2O3 wafers-are investigated to determine their intrinsic hydrophobicity and any changes upon exposure to the atmosphere. The properties of metal oxide thin films are compared to those of single-crystal alpha-Al2O3, alpha-SiO2, and Y/ZrO2. Contact angle measurements with water combined with X-ray photoelectron spectroscopy studies are applied to determine the hydrophobicity and elemental content of the metal oxides. Both the single-crystal and thin-film metal oxides are found to be intrinsically hydrophilic following a rapid thermal-processing procedure. Upon exposure to air, the investigated metal oxide surfaces become increasingly hydrophobic, correlated to the adsorption of carbonaceous species. Metal oxide thin films deposited by ALD exhibit the same hydrophobicity behavior as their single-crystal equivalents.