Laser Arc Coating

The laser arc process is a specialized variant of vacuum arc evaporation (ARC) and is classified as a PVD process. The pulsed laser specifies the ignition point at a high frequency. This combines all the advantages of the robust arc process with the controllability of the laser. This offers many process advantages, but above all it enables the stable deposition of ta‑C coatings. However, other materials that do not work with conventional arc processes can also be deposited using laser arc, e.g., MoS₂ solid lubricant films.

Laser arc technology offers the following advantages over classic arc processes:

• Uniform Layer Thickness Distribution
• Defect-free Coatings by Plasma Filtering
• Long-term Stable Coating Process
• Deposition of Doped Layers
• Deposition of MoS₂ Layers

The laser-arc plasma source acts as a line source. As a result, the carbon plasma produces a very uniformly distributed ta-C layer at the point of impact on the sample holder. A coating homogeneity of 100 ± 2% can be achieved at a coating height of 0.5 m. This enables the deposition of ultra-thin layers in the thickness range of a few nanometers, e.g., as functional, protective, or barrier layers for electrode or sensor applications. Even intense interference color layers can be deposited with a high degree of uniformity. Above all, however, the laser arc source with its homogeneous layer thickness distribution is suitable for continuous and inline coating concepts.

By deflecting the coating plasma using electric and magnetic fields, it is possible to separate the macro particles that are inevitably vaporized along with the coating, thereby achieving effective plasma filtration.

Without filtration, the particles are incorporated into the growing layer and create a defective, rough surface.

Filtering achieves virtually defect-free, smooth layers. The ta‑C layers produced with plasma filters can be used directly without post-smoothing.

The carbon-coating plasma is generated by the continuous ablation of a rotating, cylindrical graphite cathode, on which a pulsed laser scanning rapidly up and down triggers the arc discharges. The large supply of graphite material is sufficient for countless coating processes until the cathode is depleted. This means that there is no longer any limit to the layer thickness in terms of cathode consumption; layer thicknesses of >100 µm ta‑C can be deposited in a batch process. The long cathode service life is also of great importance for continuous and inline coating concepts. No other arc process is capable of running coating processes for such long periods without interruption and under constant deposition conditions.

Laser arc technology also allows the vaporization of materials other than pure carbon. To do this, the graphite cathodes are replaced with suitable alternative materials, e.g., graphite + X composites. Laser arc vaporization is achieved by adjusting the discharge parameters.

In this way, doping with boron, silicon, molybdenum, tungsten, iron, or copper can be produced. It is also possible to incorporate elements from gases such as N₂.

Laser arc technology can be used to deposit mechanically very robust MoS₂ layers, which can then be used as solid lubricants for bearings and other components in space and vacuum applications. In contrast to sputtered MoS₂, laser arc layers are significantly denser, harder, and less dependent on component contours.