Structural, optical and hydrophilic properties of nanocrystalline TiO2 ultra-thin films prepared by pulsed dc reactive magnetron sputtering

TiO2 ultra-thin (15 nm) films were deposited on silicon wafers (100) and glass slides by pulsed dc reactive magnetron sputtering in an ultra-high vacuum (UHV) system. The effects of substrate temperature, from room temperature to 400 °C, on structural, optical, and hydrophilic properties of the obtained films have been investigated. The structure of the films was characterized by grazing-incidence X-ray diffraction, high-resolution transmission electron microscopy, and atomic force microscopy. The optical properties were determined by UV–vis spectrophotometer and spectroscopic ellipsometry. The hydrophilic properties of the films, after exposed to ultraviolet illumination, were analyzed from contact angle measurements. The results suggested that the substrate temperature at 300 °C was critical in the crystalline phase transformation from amorphous to anatase in the TiO2 films. The obtained films exhibited good qualities in the optical properties, in addition to excellent photo-induced hydrophilic activities.

Research highlights
► TiO2 ultra-thin (15 nm) films were prepared by dc reactive magnetron sputtering.
► Primary deposition condition was the substrate temperature.
► Several techniques were used to characterize the physical and optical properties.
► 300 °C was the critical temperature to the TiO2 phase transformation.
► The ultra-thin films demonstrate excellent super-hydrophilic properties.