Wettability of Y(2)O(3): A Relative Analysis of Thermally Oxidized, Reactively Sputtered and Template Assisted Nanostructured Coatings

The wettability of reactively sputtered Y(2)O(3), thermally oxidized Y-Y(2)O(3) and Cd-CdO template assisted Y(2)O(3 )coatings has been studied. The wettability of as-deposited Y(2)O(3 )coatings was determined by contact angle measurements. The water contact angles for reactively sputtered, thermally oxidized and template assisted Y(2)O(3 )nanostructured coatings were 99°, 117° and 155°, respectively. The average surface roughness values of reactively sputtered, thermally oxidized and template assisted Y(2)O(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(2)O(3) and thermally oxidized Y-Y(2)O(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(2)O(3) coatings, the surface roughness was improved by depositing a thin film of Y(2)O(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(2)O(3) (54 mJ/m(2)) and thermally oxidized Y-Y(2)O(3) coatings (43 mJ/m(2)) compared to the Cd-CdO template assisted Y(2)O(3) coating (7 mJ/m(2)).