Femtosecond laser-plasmon interference lithography for self-organization of extremely regular nanogratings with tunable periodicity.

This article focuses on achieving highly regular and tunable laser-induced periodic surface structures (LIPSS) using a hybrid film composed of an amorphous silicon coating on a copper substrate. By exploiting laser-plasmon interference, the study demonstrates that increasing the silicon film thickness from 15 to 70 nm decreases the LIPSS periodicity from 1020 to 750 nm, yielding a tuning sensitivity of 4.6 ± 0.28 nm per nm, which surpasses that of previously reported single-layer films. The enhanced tunability arises from the high refractive index of silicon, which significantly affects the effective refractive index near the metal surface and modulates the surface plasmon polariton wavelength. The oxidation-driven formation of LIPSS under femtosecond laser irradiation is identified as a primarily photochemical process, enabling nonthermal, nonablative fabrication with superior uniformity. These findings suggest promising applications in photonics, sensor technology, and surface engineering by enabling cost-effective, large-scale production of nanostructured surfaces with controllable optical properties.