Flexible metamaterials with near-infrared chirality fabricated by 1D multi-pen tip-based lithography

While three-dimensional (3D) chiral metamaterials can provide strong optical chirality, their fabrication is often challenging. Two-dimensional (2D) planar metasurfaces can also exhibit intrinsic or extrinsic chiro-optical responses only when appropriate symmetries and resonant modes are engineered; thus, realizing strong and mechanically reconfigurable near-infrared chirality on flexible substrates remains challenging. Here, we demonstrate the fabrication of quasi-3D (extended along the z-axis) dielectric chiral metamaterials using one-dimensional (1D) multi-pen equipped tip-based lithography combined with metal-assisted chemical etching (MACE) on silicon-on-insulator (SOI) substrates. Quasi-3D Si fylfot (counterclockwise-chiral) structures were obtained via MACE on SOI, released, and encapsulated in polydimethylsiloxane (PDMS), resulting in flexible chiral metamaterials. The PDMS-encapsulated quasi-3D Si fylfot structures, fabricated via vacuum-free and maskless processing under ambient conditions, exhibited a circular dichroism of approximately 30% at 1537.8 nm. PDMS flexibility allows tunable optical chirality by adjusting the degree of bending. Further advancements in fabrication, such as improved pattern uniformity and etching control, are expected to enhance optical chirality, with the combination of high chirality and flexibility enabling diverse near-infrared photonic applications.