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Abstract
In this paper, using double-layer graphene nanograting arrays on top of a titanium nitride ground plane, a tunable plasmonic sensor has been presented for mid-infrared chemical sensing applications. Utilizing the plasmonic field enhancement and near-field coupling of the double-layer graphene scheme, narrowband absorption spectra in the mid-infrared region have been achieved for the required selective characteristic of the proposed sensor. The large surface area and atomic level thickness of graphene result in high surface sensitivity, leading to the tunability of the resonant wavelength of the sensor by the chemical potential variation. Moreover, employment of titanium nitride as the ground plane benefits from its abundance and low cost, fabrication stability, high melting point, and biocompatibility compared to metallic plates. Using finite-difference time-domain numerical simulations, it has been shown that the proposed sensor yields high sensitivity and a figure of merit of 3188.8 nm/RIU and ${9.1}\,\,{\rm{RIU}^{ - 1}}$, respectively, in the refractive index range of 1.31–1.39. To prove the feasibility of the design for chemical sensing applications, the sensor response in contact with organic aromatic pollutants in water has also been investigated, demonstrating a high sensitivity of 29,250 nm/RIU and a figure of merit of ${83.5}\,\,{\rm{RIU}^{ - 1}}$.
© 2019 Optical Society of America
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