Uniform subwavelength high-aspect ratio nanogratings on metal-protected bulk silicon produced by laser-induced periodic surface structuring
Kirill Bronnikov, А. В. Достовалов, V. S. Terentyev, Sergey A. Babin, A. G. Kozlov, Е. В. Пустовалов, Evgeny L. Gurevich, Alexey Zhizhchenko, Aleksandr A. Kuchmizhak
Abstract
Formation of highly ordered nanostructures on a crystalline silicon surface is highly demanded for novel optoelectronic and nanophotonic designs pushing toward development of inexpensive and high-performing nanostructuring technologies. Here, we demonstrate that laser-induced periodic surface structuring of c-Si protected by a thin Hf over-layer allows one to fabricate extremely uniform high-aspect-ratio gratings with a characteristic periodicity of ≈900–950 and 450 nm. Corresponding ordering originates from interference of incident IR femtosecond laser pulses with surface plasmons as well as doubling of the grating period via interference of counter-propagating plasmons. A high-melting-point Hf over-layer regulates the c-Si ablation in the plasmon-mediated interference maxima and prevents its excessive oxidation upon multi-pulse exposure in ambient environment. Considering unique high-aspect ratio morphology (a depth-to-period ratio of up to 1.24 and a depth-to-width ratio of up to 8) of the reported nanogratings, their outstanding uniformity, and rather fast printing rate of ≈0.2 mm2/s as well as possibility for its further upscaling, we envision high practical applicability of this technology in novel optoelectronic devices, visible and near-IR optics, all-dielectric metasurfaces, and sensors.