Structural coloration of stainless steel with planar thin-film surface cavity structure

The esthetic functions of metals are becoming increasingly significant, as their application fields are rapidly extending into mobile electronics, home appliances, surface decoration/art, and building interiors. Herein we present a simple surface structure that produces vivid structural colors on stainless steel (STS). The structure consists of a thin metal layer deposited on a dielectric film, in which the metal layer can adjust the amount of light incident onto the dielectric and strengthens the interference effect. A wide variety of colors, including blue, green, pink, purple, scarlet, and yellow, are produced simply by changing the thicknesses of the dielectric and metal layers. An important finding is that the refractive indices of the thermally evaporated Ag and Au layers are strongly thickness-dependent, which allows color tuning by varying the thickness of the metal layer only. Consequently, color images can also be printed by selectively depositing a metal layer (Au or Ag) on a uniform dielectric film. The results of this study provide a simple, scalable route to produce vivid structural colors on bulk metals and may find diverse applications, including surface decoration, product identification, perfect absorbers, and reflective color filters.