DLC films deposited at room temperature by reactive Magnetron sputtering and by an anode layer source - a comparative study

We report on the structural, mechanical and surface properties of diamond-like carbon films (DLC) deposited by employing reactive pulsed DC magnetron sputtering of graphite in argon/acetylene atmosphere and by the use of a special ion gun working with acetylene as carbon precursor. The goal of this study was to work out and discuss the most promising advantages of the two named DLC deposition techniques, in order to cover the needs for practical applications of these films. It was found, that the ion beam process using the anode layer source allows the deposition of defect-free films with high hardness (36±1 GPa) and reduced elastic modulus values (180±4 GPa). However, the disadvantage of this method is the very low deposition rate of the coatings of ~4 - 10 nm · min^-1. Sputtering is the favoured process when higher deposition rates as well as not completely defect-free films are necessary. A highest hardness of 23.3±0.3 GPa and a reduced elastic modulus of 161±4 GPa were found for the sputtered films. Deposition rates of a-C:H coatings could be tuned up to ~33 nm · min-1 for the sputtering processes. Film properties could be mainly varied by the discharge voltage when using the anode layer source or by adjustment of the acetylene/argon-ratio and the bias voltage during sputter deposition. Sputtered a-C:H films with a higher overall sp3 binding content (C–C, C–H) show lower diamond-like character (less disordering), whereas films deposited with the anode layer source show a higher overall sp3 content and thus higher diamond-like character. In general, the films deposited by the anode layer source were found to be ultra-smooth which was derived from an averaged roughness of the film surfaces of down to ~0.1 nm, whereas the sputtered films showed minimum roughness values of ~1 nm.