The wettability of reactively sputtered Y 2O 3, thermally oxidized Y-Y 2O 3 and Cd-CdO template assisted Y 2O 3 coatings has been studied. The wettability of as-deposited Y 2O 3 coatings was determined by contact angle measurements. The water contact angles for reactively sputtered, thermally oxidized and template assisted Y 2O 3 nanostructured coatings were 99°, 117° and 155°, respectively. The average surface roughness values of reactively sputtered, thermally oxidized and template assisted Y 2O 3 coatings were determined by using atomic force microscopy and the corresponding values were 3, 11 and 180 nm, respectively. The low contact angle of the sputter deposited Y 2O 3 and thermally oxidized Y-Y 2O 3 coatings is attributed to a densely packed nano-grain like microstructure without any void space, leading to low surface roughness. A water droplet on such surfaces is mostly in contact with a solid surface relative to a void space, leading to a hydrophobic surface (low contact angle). Surface roughness is a crucial factor for the fabrication of a superhydrophobic surface. For Y 2O 3 coatings, the surface roughness was improved by depositing a thin film of Y 2O 3 on the Cd-CdO template (average roughness = 178 nm), which resulted in a contact angle greater than 150°. The work of adhesion of water was very high for the reactively sputtered Y 2O 3 (54 mJ/m 2) and thermally oxidized Y-Y 2O 3 coatings (43 mJ/m 2) compared to the Cd-CdO template assisted Y 2O 3 coating (7 mJ/m 2).
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