Amorphous hydrogenated carbon films deposited by plasma enhanced chemical vapor deposition (PECVD) in a methane atmosphere were exposed to carbon tetrafluorine plasma. The r.f.-plasma treatments were performed with a chamber pressure of 8Pa and a self-bias voltage, V b , between −100 and −600V. The treatment time varied from 5 to 160min. A contact angle of approximately 135° was obtained after 10min of CF 4 r.f.-plasma treatment at a self-bias voltage of −350 or −600V and after 160min of CF 4 r.f.-plasma treatment at self-bias of −100V. The modification of the surface roughness was assessed by atomic force microscopy, which showed an increase of up to a few nanometers for the longer treatment times. The surface layer was analyzed by low energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS). The chemical bonds were probed using XPS and two chemical ambients were dominant: pairs of bonded carbon atoms and carbon bonded to one fluorine atom. The content of fluorine measured by LEIS at the sample surface increased with the treatment time. When the contact angle reached its maximum value, LEIS results were nearly independent of V b , indicating that the chemical composition of the outermost layer of the sample plays an important role in the control of the surface wettability.