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

Abstract

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 α-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 α-Al2O3, α-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.

Enhanced Hydrophobicity of CeO2 Thin Films by Surface Engineering

“…The initial values of WCA for the as-deposited ceria stay below 60°, defining the surface as hydrophilic. Such wetting behavior corresponds well with numerous works [6]-[9],[16]-[19] and confirms the idea of the intrinsic hydrophilicity of CeO2. The obtained results demonstrate a significant increase of the hydrophobicity after deposition of the carbon containing molecules.…”

Materials and Methods for High‐Efficiency Perovskite Solar Modules

“…There are several methods of improving the wettability of coating solutions. Inorganic charge extraction materials such as TiO 2 , SnO 2 , NiO, NiMgLiO, BaSnO 3 , and other metal oxides are typically hydrophilic, [ 91 ] which means that a polar solvent and an ionic liquid such as perovskite precursor solution can easily be spread on substrates based on these materials. In contrast, as organic charge extraction materials such as polymeric HTMs of PTAA (poly (triaryl amine)), TFB (poly (9,9‐dioctylfluorene‐alt‐ N ‐(4‐sec‐butylphenyl)‐diphenylamine)), and TPD (poly( N , N '‐bis‐4‐butylphenyl‐ N , N '‐bisphenyl)benzidine) are generally hydrophobic, [ 92 ] additional techniques are required to enhance the interface between the substrate and loaded precursor solutions.…”

Corrosion of One-Step Superhydrophobic Stainless-Steel Thermal Spray Coatings

“…From previous studies, it can be hypothesized that the WCA will plateau, indicating carbon adsorption saturation, within about a week where significant increases are observed within the first 48h. 35,47 As seen in the supporting information in Figure S5, the WCA values over time do not change significantly. In fact, the hydrophobicity decreases slightly with increasing exposure time.…”

“…The origin of REO hydrophobicity was proposed to be due to their unique electronic structure that inhibits hydrogen bonding with interfacial water molecules, , while some recent studies countered with evidence that the adsorption of carbon contaminates (volatile organic compounds, CO 2 , etc.) is responsible for the apparent hydrophobic nature of the inherently hydrophilic materials. ,− Although the mechanism of wetting is still under debate, this method is extremely advantageous since SPPS is industrially scalable, eliminates the need for a surface energy decrease post modification step, and results in coatings that are extremely robust. Despite their success and abundance, REOs are costly due to production difficulties encountered.…”

“…is responsible for the apparent hydrophobic nature of the inherently hydrophilic materials. 31,[34][35][36] Although the mechanism of wetting is still under debate, this method is extremely advantageous since SPPS is industrially scalable, it eliminates the need for a surface energy decrease post modification step, and the resulting coatings are extremely robust. Despite their success and abundance, REOs are costly due to production difficulties encountered.…”