The reversible wettability of Ti containing amorphous carbon films by UV irradiation

The Ti-containing amorphous carbon (a-C:Ti) deposited by the off-plane double bend (OPDB) Filtered Cathodic Vacuum Arc (FCVA) technique has been shown to exhibit very good mechanical properties such as low stress and ultra-high hardness and electrochemical properties. Further studies reveal that a-C:Ti films have a hydrophobic surface (contact angle with water >90°). This is mainly due to the formation of Ti-O bond when the samples are exposed to the ambient air. In this paper, we show that with ultraviolet (UV) laser treatment, the contact angle of a-C:Ti films with water could be reduced to be as low as 36.2°, forming a hydrophilic surface. After storing the film in ambient air for 3 h, the contact angle increased to 80° and the film recovered back to the original hydrophobic condition. We attributed this to the absorption of hydroxyl groups on the surface by the photocatalysis reactions of TiO2. This behavior makes the film a good potential candidate for self-clean coatings.