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.