Network Modification of DLC Coatings to Adjust a Defined Surface Energy

Abstract

In addition to the well-known properties of diamond-like-carbon (DLC) coatings, the surface tension is a new criterion to characterize this kind of thin films. To influence the surface tension of DLC coatings, their structure is modified by the incorporation of different elements like fluorine or silicon into the matrix of the amorphous network. Furthermore, the surface tension can be strongly influenced by the deposition parameter. With the appropriate reactive gas and process parameter it is possible to adjust separately the polar and the dispersive components of the surface tension. Using fluorinated hydrocarbons an almost PTFE-like coating with a surface tension of 22 mN/m is realized. Since halogenous monomers are very controversial it is desirable to find other reactive gases for modifying the surface tension on the basis of amorphous hydrocarbon layers. First investigations with silicon containing monomers point out the possibility to prepare hard coatings with a surface tension also comparable to PTFE but with a much better microhardness of about 15 GPa instead of 6 GPa for fluorinated thin films or 0.3 GPa for PTFE, respectively. To calculate the surface tension of plasma polymerized thin films, the applicability of contact angle measurements (sessile-drop method) is investigated first by comparing different approaches for the adhesion energy and evaluation methods, respectively.