Localized Surface Plasmonic Resonance and Sensing Properties of Ag–MgF₂ Composite Nanotriangles

Regular nanotriangular (NT) patterns and thin films composed of a mixture of Ag and MgF 2 with different composition ratios are prepared by combining nanosphere lithography and electron beam codeposition. The plasmonic property of Ag–MgF 2 composites with a high Ag composition C Ag (≥90 at. %) are shown to be a function of C Ag as well as the size of the NTs, whereas for samples with low C Ag (<90 at. %), a nearly constant localized surface plasmon resonance (LSPR) peak appears in all samples, regardless of C Ag, NT size, or thin film, which is confirmed to be because of Ag nanoparticles formed during the deposition. Thus, the LSPR property of the composite NTs can be tuned by C Ag when C Ag ≥ 90 at. %. The resulting LSPR sensor at C Ag = 90 at. % with 500 nm diameter polystyrene nanosphere monolayer can achieve a sensitivity of 696 RIU/nm, as compared to 312 RIU/nm for the same NTs with pure Ag. This significantly improved sensitivity is due to the modified dispersion relationship of the dielectric constant by the metal–dielectric composite and will play an important role in future plasmonic material design and applications.