Pure and silver (2.5-40Â vol%) modified TiO2 thin films deposited by radio frequency magnetron sputtering at room temperature: Surface topography, energy gap and photo-induced hydrophilicity

Ag-TiO2 nanostructured thin films with silver volume fraction of 0-40% were deposited on silicon and quartz substrates by radio frequency (RF) magnetron sputtering. The phase structure, surface composition, surface topography, optical properties, and hydrophilicity of the films were characterized by X-ray diffractometer, X-ray photoelectron energy spectrometer, atomic force microscope, ultraviolet-visible spectrophotometer, and water contact angle apparatus. The relation of hydrophilic property and silver content was studied in detail. It was found that silver content influences microstructure of TiO2 thin films, and silver in the films is metallic Ag (Ag0). Hydrophilic behavior of the films increases with the increase of silver content up to 5 vol% Ag and then decreases. A suitable amount (around 5 vol% Ag) of silver addition can significantly enhance the hydrophilicity of TiO2 films. The hydrophilic behavior of the films is discussed in terms of the synergic effects of defective site, energy gap, surface roughness, and grain size.