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Title: 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 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 ofmore » REOs.« less
Authors:
;  [1] ;  [2] ;  [3]
  1. Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
  2. Department of Chemical Engineering and Applied Chemistry and Materials Science and Engineering, University of Toronto, Toronto, Ontario M5S 3E5 (Canada)
  3. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
Publication Date:
OSTI Identifier:
22412594
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 106; Journal Issue: 6; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ATOMS; CERAMICS; CERIUM OXIDES; CORROSION; ELECTRONIC STRUCTURE; HYDRATION; HYDROCARBONS; HYDROGEN; ICE; INTERFACES; MOLECULES; OXYGEN; RELAXATION; SPUTTERING; STOICHIOMETRY; SURFACES; WETTABILITY; X-RAY PHOTOELECTRON SPECTROSCOPY