Plasmonic crescent nanoarray-based surface lattice resonance sensor with a high figure of merit

Due to the natural accumulation of radiation losses arising from the localization and random arrangement of nanoparticles, the figure of merit (FOM) of localized surface plasmon resonance (LSPR) sensors is usually very low (the value is usually less than 5 RIU^-1). However, radiation losses of individual particles will be offset by adjusting the phase of the scattered field which is dependent on the structure parameters of arrays. Based on this, a two-dimensional periodic crescent nanoarray-based surface lattice resonance (SLR) sensor with a high FOM is proposed in this work. Some significant results have been obtained by mode field analysis and adjustment of structural parameters. On the one hand, the line-shape of the SLR spectrum is divided into a Fano-like line and a separate line. And the former usually has an FOM of 10¹ magnitude while the latter has an FOM of 10³ magnitude. On the other hand, the relative size of the excitation wavelengths between SLR and LSPR is also vital. The FOM is higher but resonance depth decreases faster when the relative size increases. In this work, a full width at half-maximum (FWHM) of less than 0.5 nm and FOM of more than 1000 RIU^-1 (the quality factor is more than 3000) are achieved by the proposed crescent nanoarrays. In addition, this structure demonstrates that plasmonic nanoarray-based SLR has enormous potential in trace substance detection.