Growth of Thin Film Water on α-Al2O3 (0001) : An FTIR Study

This study set out to elucidate the growth of thin film water on a hydroxylated α-Al2O3 (0001) surface using FTIR spectroscopy. The absorption of water on metal oxide surfaces, particularly aluminum oxides, alters the surface chemical reactivity and structure. We are able to detect an infrared signature due to surface bound water that is different than multilayer water. We use this infrared signature to separate and quantify the amount of water at the surface or interfacial water from the total amount of water adsorbed. Also, we use this information to model the growth of the interfacial water layer as compared to total water absorption and show that initially water does not wet the α-Al2O3 (0001) surface completely. We are able to extract a small contact angle (1.9 × 10−4) and spreading parameter (−4 × 10−10) for thin-film water growth up to ∼7 monolayer equivalents and show that thin-film water grows as droplets that conserve contact angle.