Contact angle of water on chromium nitride thin film prepared on three-dimensional materials by chromium plasma-based ion implantation

This work focused on the contact angle of a water drop on chromium nitride (CrN) film. The CrN thin film was prepared on a silicon substrate attached to materials of simple three-dimensional (3D) shapes, such as trenches and pipes. The materials were immersed in a DC (80 A) chromium cathodic-arc plasma at nitrogen gas pressure of 0.27 Pa. The voltages applied to the substrate were the pulses of −10, −20 and −30 kV for 20 μs at 400 Hz, and DC of −400 and −600 V. The processing time was 20 min. The water contact angle increased with time after preparation of the film. The initial contact angles were smaller, the surface being rather hydrophilic; they rapidly increased with time up to 5 h, and a gradual increase followed after 10 h. The temporal change and the final (48 h) value of the contact angle were independent of the position on the 3D materials. The final value of the contact angle for an application of DC −600 V was equal to that for pulse potential of −20 kV. However, the value became small when the film was prepared without an application of voltage or with an application of DC voltage below −400 V.