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

Abstract

Achieving laser-induced periodic surface structures with both excellent regularity and high tunability is a challenging task. In this study, we address this challenge by utilizing a hybrid film structure, comprising an amorphous silicon coating on a copper film, to create periodic structures through a photochemical reaction induced by laser-plasmon interference. Our experiments, corroborated by numerical simulations, demonstrate a significant decrease in structural periodicity from 1020 to 750 nm with an increase in silicon film thickness from 15 to 70 nm. This corresponds to a tuning sensitivity of 4.6 ± 0.28, which is an order of magnitude higher than that of previously reported single-layer films. This substantial tunability is due to the high refractive index of silicon, where even slight thickness variations significantly alter the effective refractive index near the metal surface, thereby modulating the plasmonic wavelength. Additionally, we investigated the influence of laser pulse durations and repetition rates on laser-induced periodic surface structure periodicity and found them to have negligible effects.