Influence of plasma conditions on the deposition of superhard amorphous films by laser and arc methods

It is now well proved that superior mechanical properties may be achieved not only with crystalline diamond but also by amorphous carbon films. They allow the unique combination of very high hardness (40 - 80 GPa), low friction (dry, against steel: 0.1 - 0.2) and high smoothness. By special measures the usually high level of intrinsic compressive stresses may be reduced down to about 1 GPa. These properties together with the low deposition temperature are made possible by using particles with high kinetic energies of some ten eV. According to the subplantation model the impinging particles penetratethe surface. In this way the film grows from the interior outwards instead of island-like condensation on the surface typical for lower energies.The subplantation growth mode allows the preparation of very smooth surfaces and due to the constraints of the surrounding the formation of sp3 bonds and a correspondingly tight three-dimensional carbon network. Thorough investigations with monoener getic ion beams have clearly shown the existence of a certain energy threshold of about 30 eV which must be exceeded for the preparation of amorphous carbon films with dominating sp3 bonds. More effective plasma sources as laser ablation and vacuum arcs show a more complex plasma state. Its influence on mechanical and optical film properties will be discussed in the following.