Femtosecond laser-induced nanoscale texturing for super-black stainless-steel surfaces

Abstract The fabrication of hierarchical micro-/nanostructures on stainless steel (SS)(SS304) surfaces provides highly efficient broadband light-trapping capability, enabling applications in photothermal conversion, infrared stealth, sensing, low-illumination imaging, solar energy harvesting, and anti-reflection optical components. In this work, we demonstrate synergistic three-dimensional micro-/nanofabrication approach by integrating subtractive and additive material processing techniques. The subtractive process employs ultrafast femtosecond-laser fabrication, enabling the formation of micro- and nanostructures through a single-step ablation process. The subsequent additive process involves controlled oxidation, which induces the growth of dense nanospikes on the hierarchical framework. Together, these processes create a graded refractive-index profile that effectively suppresses reflectivity across the UV–visible-IR spectral range. By optimizing the laser fluence, scanning interval, and scanning speed, we achieve an average total hemispherical reflectivity of ∼0.90% in the 400–1100 nm range and ∼0.75% in the 250–700 nm range corresponds to ∼99.25% absorbance. Owing to the enhanced light-trapping capability, the fabricated surfaces also exhibit superior photothermal performance, reaching significantly higher temperatures under solar irradiation compared to untreated SS. The demonstrated approach establishes a versatile platform for engineering metallic surfaces with extreme light absorption and improved photothermal response, suitable for large-area and application-oriented implementations.