Super-hydrophilic anatase TiO2 thin film in-situ deposited by DC magnetron sputtering

Abstract

The present work shows in-situ polycrystalline anatase TiO2 without annealing under the deposition condition of affluent oxygen partial pressure (≥5.67, PO2/PAr) by DC magnetron sputtering. The films tended to grow from the early random orientation to A(211) oriented polycrystalline as deposition time increases. As the oxygen gas flow rate was high, A(211) facet grew more. Therefore, oxygen partial pressure and the deposition time/thickness can be considered as the key parameters that promote the growth of A(211) facet. The study focus was the hydrophilicity due to A(211) facet measured in dark after initial one time UV exposure. The contact angle relaxation of super-hydrophilic TiO2 films was influenced by the humidity for dark storage time. The contact angle was measured after 24h from the initial UV irradiation. The measured contact angle decreased somewhat linearly with the increase of the XRD intensity ratio of A(211)/A(101) up to 50%. When it was higher than 50%, the angle saturated. XPS analysis showed that the higher the XRD intensity ratio of A(211)/A(101), the larger the area of O 1s (OH) band related to the dissociative adsorption of water. The relative amount of the surface hydroxyl group was found to be inversely proportional to the contact angle. ATR-FTIR spectra also showed that the water is adsorbed more on the formation of A(211) facet on the TiO2 surface. In summary, A(211) oriented TiO2 grains lead to dissociative adsorption of water and show better superhydrophilicity due to a sufficient amount of surface hydroxyl groups.