Deeply sub-wavelength laser nanopatterning of Si surface in dielectric fluids: Manipulation by surface plasmon resonance

Deep sub-wavelength, large-scale surface nanopatterning of silicon (Si) wafers immersed in water or carbon disulfide, in the form of ultrafine nanoripples was performed by multi-shot 1030-nm femtosecond laser exposures. Our simulations indicate the key role of surface plasmons, with their extreme wavenumbers tunable versus the dielectric permittivity of the contact dielectric fluids. The factors of the squared optical refraction index of fluids, excitation and interference of counter-propagating surface plasmons were revealed to provide in both these fluids the ultimately small (similar to 100 nm) periods of the nanoripples. The realized advanced wet laser nanopatterning of Si surfaces, unattainable via dry laser processing, paves the way toward nanoscale laser lithography.