Superhydrophobic Poly(tetrafluoro-ethylene) (PTFE) like thin films were grown using a plasma-based hybrid process consisting on sputtering a carbon target in a Ar/CF4 atmosphere. The influence of the bias voltage applied to the substrate (VBias) as well as of the gas mixture composition (%CF4) on the chemical composition, the wettability and the morphology of the deposited thin films were evaluated.

The chemical composition measured by X-Ray photoelectron spectroscopy (XPS) reveals that the fluorine content is lower than in conventional PTFE (50 at.% maximum >< 66%) and that it decreases when VBias increases (from 50 at.% for VBias = -100 V to 30 at.% for VBias = -200 V). This behaviour is associated with the preferential etching of the fluorine atoms during the plasma-assisted growth of the films. Consecutively to this etching, a self-nanostructuration enhanced by increasing VBias, is observed. As a consequence, the water contact angle (WCA) measurements range from 70° up to 150° depending on (i) the fluorine content and (ii) on the magnitude of the nanostructuration. In addition, for the films presenting the highest WCA angles, a small hysteresis between the advancing and receding WCA is observed (< 10°) allowing these films to fulfil completely the requirements of superhydrophobicity.

In order to get more understanding on the wettability mechanisms of these surfaces, the topology of the films has been evaluated by atomic force microscopy (AFM). The data reveal, for all films, a dense and regular structure composed by conic objects for which the dimensions increase with Vbias. We were able to correlate the ratio of the average height (AvH) of the objects and the average distance (AvD) between them with the WCA. Theoretical evaluations of the WCA using the Wenzel and Cassie equations with, as inputs, the features of the deposited thin films surfaces measured by AFM suggest that the wetting regime is intermediate between these two ideal situations.