Surface energy of nano-structurated ZnO films deposited on silicon.

Surface energy and work adhesion are important features for a wide range of applications such as: water repellent surfaces, self cleaning materials, anti-icing surface, antifogging devices,ensing applications and microfluidics. In this work we studied the surface wettability of nanostructured ZnO films deposited by RF sputtering using Ar-H2 plasma. Depositions were performed at room temperature. Si (100) was used as substrate. The wettability was measured by means of sessile contact angle using milliQ water (18MΩ). The surface energy was calculated by Neumann equation and the work of adhesion by means of Young – Dupre equation. The surface morphology was studied by Atomic Force Microscopy. The nano-porosity of surface was determined by means of nanoindentation measurements. The results show that the increase of hydrogen concentration in the gas mixture during deposition leads to a) an increase of the surface nano-porosity of ZnO and b) a reduction of the work of adhesion on ZnO surfaces. This result is interpreted on the basis of the Cassie-Baxter mechanism