Plasmonic Refractive Index Sensing Based on Interference in Disordered Composite Films

Abstract

The strong dispersion in the effective optical constants of plasmonic nanocomposite films is used to generate interference effects that are highly sensitive to changes in the dielectric environment of particles. Numerical simulations show that reflectance measurements on metal nanoparticle systems close to a metallic substrate have larger sensitivities to changes in the surrounding refractive index than the standard transmittance measurements of the same system when placed on a transparent substrate. The scheme is particularly advantageous in case of disordered nanoparticle systems, where the difference between reflectance and transmittance‐based sensing approaches is enhanced due to local‐field fluctuations that modify the effective optical constants dispersion. Exceptional to most plasmonic applications, in the present case, a disordered system provides larger sensitivity and figure of merit than its ordered counterpart. The key concepts suggested from numerical calculations are verified by the fabrication of metal island films coated with different dielectric layers, that confirm the superiority of the reflectance‐based sensing scheme. Overall, the present approach profits from the disorder to improve refractive index sensitivity in metal nanoparticle systems that are produced with industrially appealing techniques. Thus, the proposed scheme may be valuable for the broad implementation of low‐cost and highly efficient plasmonic sensors.