Plasmonic waveguide-mode based aluminum nanogratings for enhanced chemical and biological sensing in the UV regime

Abstract We have designed and modeled one dimensional narrow-gap aluminum nanogratings for plasmonic sensing of bulk and localized changes in the refractive index in the UV spectral region. The proposed configuration of the plasmonic sensors based on narrow-gap nanogratings allows normally light to be directly coupled into plasmonic waveguide modes in the gaps between the nanogratings, thereby alleviating the problem of employing bulky prism coupling mechanisms. The rigorous coupled wave analysis (RCWA) simulations were performed to optimize all the narrow-gap nanograting parameters such as the periodicity ‘ P ’, the gap between the nanograting walls ‘ W ’, and height ‘ H ’ of the nanogratings such that the plasmonic sensors based on these nanogratings operated in the UV spectral region and had the highest values of sensing performance characteristics. The plasmon resonance related dips in the reflectance spectra of these narrow-groove nanogratings can be tuned in the far-UV and deep-UV wavelength ranges by varying the different structural parameters of these nanogratings. Furthermore, we have defined other performance parameters like FOM bulk * and FOM localized * to account for the depth of the plasmonic resonance dip along with the sensitivity ( S ) and figure of merit ( FOM ). These narrow-gap nanogratings have localized regions of high electromagnetic fields inside the gaps between the nanogratings, which results in enhanced sensitivity of the proposed structures. We have calculated the maximum bulk sensitivity ( S ) of 190 nm RIU −1 with the figure of merit ( FOM bulk * ) of 2.567 RIU −1 in the UV region. Similarly, the highest localized sensitivity ( S s ) of 18.2 nm nm −1 and a figure of merit ( FOM localized * ) of 0.15356 nm −1 was obtained for the narrow-gap aluminum nanograting based plasmonic sensor. The high sensitivity achieved in localized and bulk sensing enables this configuration to be developed into a compact and highly robust sensor for chemical and bio-sensing applications.