Tailored a-C:H coatings by nanostructuring and alloying

The different properties of a-C:H can be tuned, either by alloying additional elements into the amorphous a-C:H or by building multilayer structures composed of two different types of a-C:H. This allows the design of optimized coatings for a wide range of applications. Multilayered a-C:H films, composed of a 60 nm Si-a-C:H adhesion layer and 300 nm multilayer structure have been deposited by a periodical variation of the sample self-bias voltage during deposition. The single layer thickness has been varied from 4 to 20 nm. The wear rate (determined by pin-on-disk measurement against a steel ball) of multilayer structures having a single layer thickness in the range of 12-14 nm, showed a drastic decrease by one decade down to 4 x 10^-18 m³ Nm^-1, compared to the multilayer systems composed of thicker or thinner single layers. Amorphous hydrogenated carbon films containing titanium in different concentrations (a-C:H/Ti) were deposited by a combined RF-PACVD and DC magnetron sputtering process. The titanium content in the carbon matrix caused cellular reactions of bone marrow cells (BMC) like enhanced cell proliferation together with a reduced osteoclast cell activity. This could make a-C:H/Ti a valuable hard coating for bone implants, by enhancing bone ingrowth through osteoblast differentiation while reducing bone resorption through osteoclast inhibition.