High-density flexible nanopatterning of silicon with scanning photonic nanojets

The growing demand for micro/nanofabrication calls for precise, reliable, and scalable processing techniques. While direct laser writing offers flexibility, the Abbe diffraction limit fundamentally restricts its ability to achieve nanometer-scale resolution. To address this challenge, we rely on a maskless colloidal lithography technique leveraging laser-driven photonic nanojets (PNJs). A self-assembled monolayer of 5 μm polystyrene microspheres generates PNJs under 1030 nm femtosecond laser irradiation, enabling the fabrication of sub-500 nm features on silicon substrates. Unlike conventional static PNJ configurations, we report on a method that employs a rotational mechanical assembly to dynamically steer PNJs through each microsphere, facilitating ultra-high-density parallel writing of arbitrary structures. However, experimental results and numerical simulations reveal significant angular-dependent variations in PNJ properties, leading to non-uniform feature sizes. We propose compensatory optimizations of laser pulse conditions to achieve angle-independent modification dimensions. Using this approach, we demonstrate the fabrication of uniform arbitrary structures with a 5-μm pitch across processed areas. This technique offers a promising route toward high-throughput parallel nanofabrication, with applications in next-generation photonic devices, optical data storage systems, and advanced micro/nano manufacturing technologies.