Dynamic tuning of surface lattice resonances via mechano-optical coupling in flexible nanoring metasurfaces

Flexible metasurfaces comprising arrays of sub-wavelength thick nanoparticles embedded in soft and transparent substrates have attracted significant research interest due to their ability to generate predictable, tunable, and reversible optical performances. In this work, we employ electron beam lithography combined with wet-etching techniques to fabricate flexible metasurfaces of gold elliptical nanorings arranged in square or triangular arrays on polydimethylsiloxane. Scanning electron microscope tests conducted on the soft substrate demonstrate the feasibility of the pattern transfer technique at the nanoscale, as well as the reliability of the in situ optical characterization. Continuous monitoring of reflectance under strain, complemented by numerical simulations and theoretical analysis, reveals intriguing optical behaviors for these metasurfaces, including Fano features in surface lattice resonances, spectral blueshifts in localized surface plasmonic resonances, and color changes from purple to green and orange. By integrating metasurfaces with different characteristics into a chessboard-like pattern, we propose the configuration of a flexible strain map for contactless investigation of localized surface strain, which also provides opportunities for information encryption by encoding the varied resonances under strain.