Influence of Plasma Conditions on the Deposition of Superhard Amorphous Carbon Films by Laser and Arc Methods

Abstract

Amorphous carbon films with dominating sp 3 bonds in the C-C network can be deposited by energetic particle beams if the following pre conditions are fulfilled: - high kinetic energy of all particles in the range of some ten to some hundred eV for sufficient subplantation into the surface layer, - sufficient low deposition temperature for avoiding any relaxation towards graphitic bonding, - avoidance of hydrogen, which could occupy carbon bonds and thus weakens the carbon network. Pulsed laser irradiation and pulsed vacuum arc discharges are suitable methods for producing fully ionized plasma beams with high kinetic energies in the required range. For an ArF excimer laser, laser controlled vacuum arc (Laser-Arc) and the magnetically filtered High Current Arc (HCA) the plasma parameters are determined by optical short time emission spectroscopy and by retarding field analysis. In dependence on the irradiation or discharge conditions, the temperature of the fully ionized plasma lies between 1.5 and 2.2 eV, the main kinetic energy (without bias) between 20 and 60 eV, the energy spread between 20 and 50 %. These plasma parameters correlate with macroscopic properties. Young's modulus > 700 GPa (corresponding to hardness > 70 GPa and sp 3 fraction > 70%) has been realized. By a special interlayer and film design, internal compressive stresses has been reduced to about 1 GPa. The optical gap, which determines the transparency is increased to about 2.5 eV. Structural heterogeneity down to the micrometer scale is characterized by micro-Raman spectroscopy, at the nanometer level by transition electron microscopy. Nanometer multilayer stacks with alternating sp 3 content can be produced by systematic variation of deposition parameters. Under special fullerenlike nanosperes (or nanotubes) grow in the film notwithstanding the dominating sp 3 nature. The potential of these carbon films and especially their nanometer scaled modifications for a variety of industrial applications in tribology, electronics, ananlytics and others and the necessary adaption of optimized plasma sources is shortly discussed.