Tarnishing of silver subwavelength slit gratings and its effect on extraordinary optical transmission

We study the impact of tarnishing of silver subwavelength gratings on their optical performance. We report that in the course of months under regular laboratory conditions, the gratings undergo tarnishing very differently from plain silver films: instead of thin layer of evenly distributed silver sulfide, a random pattern of rare larger crystals is formed across the grating area. As typical of plasmonic metamaterials, the gratings appear to be very sensitive to the arising structural disorder and show a very specific modification of the optical transmittance spectra – total degradation of the Wood diffraction anomaly and attenuation of the near-infrared transmission peak. The identified ‘optical fingerprints’ of the microscopic grating contamination pave a way for prospective plasmonic sensor applications.