Coloration of metallic and/or ceramic surfaces obtained by atomic layer deposited nano-coatings

By depositing by physical vapor techniques single layer coatings, the tailoring of their coloration is generally complex because a given color can be obtained only by very high composition control. Moreover, PVD processes are expensive and complicated to perform on curved objects. They exhibit intrinsic defects (columnar structures, pores) which can affect other functional properties like barrier protection. Atomic Layer deposition (ALD) technology delivers on different materials conformal coatings with very low defectiveness, suitable e.g. for barriers to ion release, etc. A more straightforward coloration is obtained by a combination of two types of layers with different refraction index, deposited to high thickness precision. Different multilayer configurations were sought as optical coatings to modify the typical coloration of several metallic and/or ceramic surfaces. Computer simulation studies were performed to design the thickness and architecture of suitable multilayer structures, to a total thickness of the order of 100 nm, in order to modify the typical coloration of some materials, without altering the other physical and chemical properties. The most promising nano-layered structures were then deposited by ALD and tested with regard to their optical properties. Their total thicknesses were specified in such a way to be technically feasible and compatible with future industrial production. The materials employed in this work to build the optical coatings, are two oxides (Al2O3, TiO2) deposited at temperatures between 120 and 250°C and two nitrides (AlN, TiN), which need deposition temperatures between 350 and 400 °C. The possibility of using such modern deposition technology for aesthetic and decorative purposes, while maintaining the functional properties, opens perspectives of industrial applications. KEYWORDS: Optical design; colored ceramic layers; atomic layer deposition (ALD).