Decorative coatings with different properties
Metallic effect layers
Substrate surfaces can be finished with decorative metal coatings using magnetron sputtering or thermal vapour deposition. In doing so, the PVD vacuum process can be carried out in a way that forms either a matte or a metallically high-gloss coating. The colour spectrum ranges from deep tones of black or blue to copper and bronze colours to bright gold and silver effects. Metal effect coatings are often coated with a transparent oxide protective layer to preserve their optical brilliance over a long period of time.
Typical effect metals
- Chromium (Cr)
- Ruthenium (Ru)
- Copper (Cu)
- Gold (Au)
- Silver (Ag)
Dielectric effect coatings (interference colours)
Relatively thick oxide layers with layer thicknesses of greater than half the wavelength of the light (d > λ/2) reflect the incident light at their boundary surfaces in such a way that effective colour shifts occur as a result of interference. All of the colours of the rainbow can be produced by selecting a suitable layer thickness. If there are special requirements for the reflection and transmission behaviour beyond the colour effect, then combinations of low-and high-index dielectric materials can be stacked to produce the desired result.
Oxide deposited by reactive sputtering for example
- Silicon dioxide (SiO2)
- Titanium oxide (TiO2)
Decorative applications such as colour reflections can be produced by reactive sputtering of oxide layers (interference colours)
Polymer substrates can be coated using the PVD process as well. Here, thin films are used to colour device exteriors (housings for mobile phones)