Extremely Ultranarrow Linewidth Based on Low-Symmetry Al Nanoellipse Metasurface.

Plasmonic nanostructures with ultranarrow linewidths are of great significance in numerous applications, such as optical sensing, surface-enhanced Raman scattering (SERS), and imaging. The traditional plasmonic nanostructures generally consist of gold and silver materials, which are unavailable in the ultraviolet (UV) or deep-ultraviolet (DUV) regions. However, electronic absorption bands of many important biomolecules are mostly located in the UV or DUV regions. Therefore, researchers are eager to realize ultranarrow linewidth of plasmonic nanostructures in these regions. Aluminum (Al) plasmonic nanostructures are potential candidates for realizing the ultranarrow linewidth from the DUV to the near-infrared (NIR) regions. Nevertheless, realizing ultranarrow linewidth below 5 nm remains a challenge in the UV or DUV regions for Al plasmonic nanostructures. In this study, we theoretically designed low-symmetry an Al nanoellipse metasurface on the Al substrate. An ultranarrow linewidth of 1.9 nm has been successfully obtained in the near-UV region (400 nm). Additionally, the ultranarrow linewidth has been successfully modulated to the DUV region by adjusting structural parameters. This work aims to provide a theoretical basis and prediction for the applications, such as UV sensing and UV-SERS.