Tunable multiband metasurfaces by moire nanosphere lithography

Moire nanosphere lithography (MNSL), which features the relative in-plane rotation between two layers of self-assembled monodisperse nanospheres as masks, provides a cost-effective approach for creating moire patterns on generic substrates. In this work, we experimentally and numerically investigate a series of moire metasurfaces by MNSL. Due to the variety of gradient plasmonic nanostructures in arrays, single moire metasurfaces can support multiple localized surface plasmon (LSP) modes with a wide range of resonant wavelengths from similar to 600 nm to similar to 4200 nm. We analyze the origin of the LSP modes based on the optical spectra and near-field electromagnetic distributions. In addition, we fabricate and analyze the metasurfaces with high-density nanogap structures. These nanogap structures support plasmonic gap modes with significant field enhancements. With their tunable multiband optical responses from visible to near-infrared to mid-infrared regimes, these moire metasurfaces are applicable for ultrabroadband absorbers, multiband surface-enhanced infrared and Raman spectroscopy, and broad-band single-molecule spectroscopy.