Aluminum surface lattice resonances for enhanced near-infrared performance in asymmetric environments.

Aluminum (Al) is a cost-effective alternative to noble metals for plasmonics, particularly in the ultraviolet (UV) and visible regions. However, in the near-infrared (NIR) region, its performance is hindered by interband transitions (IBTs) at around 825 nm, leading to increased optical losses and broad resonances. Surface lattice resonances (SLRs) offer a promising solution by enhancing the plasmonic quality factor (-factor) through coherent coupling of localized surface plasmon (LSP) modes with Rayleigh anomalies. Although high- SLRs have been demonstrated in homogeneous environments, achieving similar enhancements in asymmetric media such as air remains a challenge. This study presents a novel approach for improving the factor of aluminum in air by utilizing SLRs in aluminum nanoparticle (NP) arrays fabricated electron beam lithography (EBL) on a high refractive index indium tin oxide (ITO) substrate. The ITO substrate enhances long-range coupling between NPs, reinforcing coherent interactions. Using absorption micro-spectrometry and finite-difference time-domain (FDTD) simulations, we demonstrate factors reaching 110 in air, significantly exceeding typical values in IR in an asymmetrical surrounding medium. Our results establish aluminum as a viable low-cost material for high-performance plasmonic applications in sensing, telecommunications, and optoelectronics.