Interference-Enhanced Plasmonic Photocatalysis via Color Laser Engraving on Stainless Steel

Color laser engraving on stainless steel produces structural colors by forming oxide layers of controlled thicknesses via fiber laser processing. By tuning laser parameters, we generated several distinct coloration patterns on 304 stainless steel, each associated with a different thickness of the oxide layer. Then, a SiO₂ layer was deposited on the colored surface. Owing to the optical path difference introduced by the total stack thickness of the stainless steel oxide layer and the SiO₂ layer, light reflected from the top of the SiO₂ layer and the bottom of the stainless steel oxide layer at specific wavelengths could interfere. Subsequently, Ag nanocubes (NCs) were placed atop this stack to exhibit enhanced surface plasmon resonance (SPR)-mediated photocatalytic activities resulting from this interference effect, probed by using surface-enhanced Raman scattering (SERS) of the <i>p</i>-aminothiophenol to <i>p</i>,<i>p</i>'-dimercaptoazobenzene (PATP-to-DMAB) conversion under 633 nm irradiation. The best photocatalytic performance was achieved when the total optical path difference satisfied the constructive interference condition, approaching an integer multiple of the incident light's wavelength. With a 46.2 nm SiO₂ layer, this condition was met for the red coloration sample, whereas with a 132.8 nm SiO₂ layer, it shifted to the yellow coloration sample. Therefore, the interference engineering through oxide thickness tuning might suggest a novel strategy for improving SPR-mediated photocatalytic performance, and this work demonstrates clear practical and experimental novelty by providing a simple, low-cost approach to tune interference-enhanced plasmonic photocatalysis on real metallic substrates.