Vivid structural colors produced on stainless steel

As the esthetic functions of metals have attracted increasing attention, their coloration is a significant issue in scientific and technological aspects. We here demonstrate that vivid structural colors can be produced on stainless steel. The structure consists of a SU-8 layer coated on the surface of bulk stainless steel that has a one-dimensional texture of 500 nm period. Polarization-dependent, diverse colors are produced simply by changing the thickness of the dielectric overlayer. The colors result from the surface plasmon resonance and guided mode resonance of incident light, which occur on the metal surface and inside the dielectric layer, respectively. Simulation based on the finite-difference time-domain method supports the experimental results, showing that the layer thickness influences the characteristic wavelengths of both resonances and the resulting colors. Color image patterns are also printable on the surface of stainless steel by irradiating a solution-coated SU-8 layer with a pulsed ultraviolet laser beam. The final thickness of the photopolymeric SU-8 layer is locally controlled by adjusting laser fluence. The current study provides a simple route to produce diverse structural colors on metals and may find many applications including surface decoration, product identification, and anti-counterfeiting.