Role of surface oxygen-to-metal ratio on the wettability of rare-earth oxides

Hydrophobic surfaces that are robust can have widespread applications in drop-wise condensation, anti-corrosion, and anti-icing. Recently, it was shown that the class of ceramics comprising the lanthanide series rare-earth oxides (REOs) is intrinsically hydrophobic. The unique electronic structure o...

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Bibliographic Details
Published in:Applied physics letters 2015-02, Vol.106 (6)
Main Authors: Khan, Sami, Azimi, Gisele, Yildiz, Bilge, Varanasi, Kripa K.
Format: Article
Language:English
Subjects:
Applied physics
Cerium oxides
Chemical bonds
Contact angle
Contaminants
Corrosion prevention
Deicing
Electronic structure
High vacuum
HYDRO ENERGY
Hydrogen bonding
Hydrophobicity
Molecular structure
Oxygen atoms
Rare earth compounds
Rare earth oxides
Stoichiometry
Water chemistry
Wettability
Wetting
X ray spectra
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Summary:Hydrophobic surfaces that are robust can have widespread applications in drop-wise condensation, anti-corrosion, and anti-icing. Recently, it was shown that the class of ceramics comprising the lanthanide series rare-earth oxides (REOs) is intrinsically hydrophobic. The unique electronic structure of the rare-earth metal atom inhibits hydrogen bonding with interfacial water molecules resulting in a hydrophobic hydration structure where the surface oxygen atoms are the only hydrogen bonding sites. Hence, the presence of excess surface oxygen can lead to increased hydrogen bonding and thereby reduce hydrophobicity of REOs. Herein, we demonstrate how surface stoichiometry and surface relaxations can impact wetting properties of REOs. Using X-ray Photoelectron Spectroscopy and wetting measurements, we show that freshly sputtered ceria is hydrophilic due to excess surface oxygen (shown to have an O/Ce ratio of ∼3 and a water contact angle of ∼15°), which when relaxed in a clean, ultra-high vacuum environment isolated from airborne contaminants reaches close to stoichiometric O/Ce ratio (∼2.2) and becomes hydrophobic (contact angle of ∼104°). Further, we show that airborne hydrocarbon contaminants do not exclusively impact the wetting properties of REOs, and that relaxed REOs are intrinsically hydrophobic. This study provides insight into the role of surface relaxation on the wettability of REOs.
ISSN:0003-6951
1077-3118
DOI:10.1063/1.4907756