Hydrogen isotope exchange in amorphous hydrocarbon layers: plasma-deposited a-C:H and ion-saturated carbon

Although hard hydrocarbon layers prepared by glow discharge (a-C:H/D films) display hydrogen contents similar to those observed in graphite saturated by hydrogen implantation, the hydrogen-recycling behaviour of both films appears to be significantly different. This is concluded from isotopic exchange measurements during 8 keV D+ and 11 keV H+ irradiation of hydrogenated and deuterated layers. The a-C:H/D films display a strong initial depletion, which slowly gives way to a resaturation at increasing ion fluence. In the case of saturated carbon, the initial depletion appears much weaker or is even missing. This difference may be explained qualitatively by different binding states in the films resulting from the different conditions or preparation. (author)