Ultra hydrophobic wetting behaviour of amorphous carbon films

Abstract

Carbon films are distinguished by their broad structural variability and a correspondingly wide range of properties varying from diamond-like to graphite-like. This variability is determined by the relation of diamond bonds (sp3) to graphitic bonds (sp2) and can be influenced by addition of other elements. The highest degree of diamond-likeness, e.g. expressed by high hardness, is achieved in pure carbon films. Such super hard films, so-called tetrahedral bonded amorphous carbon films (ta-C), reach a hardness from 40 GPa up to 80 GPa and a Young's modulus from 400 GPa up to 800 GPa.By incorporation of additional elements, not only the mechanical properties but also the surface energy can be varied. PTFE-like properties can be obtained by addition of fluorine or other elements. At Fraunhofer IWS Dresden such doped amorphous carbon films (a-C:X) have been deposited by a special pulsed vacuum-arc technique, the laser-induced pulsed arc (Laser-Arc). The deposition process is characterized by producing a high activated carbon plasma from a pure or doped graphite cathode and its deposition on substrates under vacuum or reactive conditions.The mechanical properties of the doped a-C:X-films were investigated in dependence on the content of the doped elements. Furthermore, the surface energy was determined by means of contact angle measurements.To get ultra hydrophobic properties of a surface additionally to a low surface energy a defined structuring of the surface topography is necessary. Different kinds of such structuring methods and their effects in conjunction with a doped a-C:X-film on the super hydrophobic behaviour are shown.