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Improvement of the sensitivity of chalcogenide-based infrared sensors dedicated to the in situ detection of organic molecules in aquatic environment

The aim of this study was to develop mid-infrared chalcogenide sensor and perform its functionalization by polymers in order to detect various hydrocarbon pollutants in water and to ensure an efficient attenuation of the water absorption bands. Selenide waveguides were fabricated by radiofrequency magnetron sputtering on silicon substrates using two different glass target compositions, for cladding and guiding layers. A hydrophobic polymer was deposited on the surface of zinc selenide prisms to allow its characterization by ATR-FTIR (Attenuated Total Reflectance-Fourier Transform InfraRed) spectroscopy. Benzene, toluene and ortho-, meta- and para-xylenes in solutions of distilled water at concentrations ranging from 10 ppb to 20 ppm were simultaneously detected and the measured limit of detection was determined to be equal to 250 ppb. However, the limit of detection must be improved to meet environmental standards. To achieve this goal, metallic nanostructures were deposited on the surface of the chalcogenide waveguides to increase the sensitivity of the future optical sensor thanks to the plasmon resonance phenomena. Thus, the fabrication of a heterostructure composed of gold nanoparticles deposited by electron beam evaporation was performed on a slab selenide waveguide in order to assess SEIRA (Surface-Enhanced InfraRed Absorption) effect.