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

• Computer simulation is done to design multilayers made of Al2O3, TiO2, AlN, and TiN.
• Total thickness (< 120 nm) is specified to be compatible with industrial production.
• The most promising nano-layered structures are then produced and optically tested.
• An ultrathin TiN (20 nm) top layer is able to confer intense blue color to metals.

By depositing single layer coatings by means of physical vapor techniques, tailoring of their coloration is generally complex because a given color can be obtained only by very high composition control. Physical vapor deposition (PVD) processes are expensive and cannot be easily used for obtaining conformal coating on three-dimensional objects. Moreover PVD coatings exhibit intrinsic defects (columnar structures, pores) that affect their functional properties and applications such as barrier layers.Atomic layer deposition (ALD) technology delivers conformal coatings on different materials with very low defectiveness. A straightforward coloration can be obtained by a combination of two types of layers with different refraction index, deposited to high thickness precision.Computer simulation studies were performed to design the thickness and architecture of multilayer structures, to a total thickness of approximately 100 nm, suitable to modify the typical coloration of some materials, without altering their 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 study to build the optical coatings, are two oxides (Al2O3, TiO2) deposited at 120 °C and two nitrides (AlN, TiN), which need a deposition temperature of 400 °C.The possibility of using such modern deposition technology for esthetic and decorative purposes, while maintaining the functional properties, opens perspectives of industrial applications.