An optical sensor of ammonia gas, based on the surface plasmon resonance (SPR) method has been investigated. The surface plasmon resonance (SPR) is very sensitive, and so is the optical technique used in chemical sensing. The angle of incident of light at which a resonant effect is observed, as well as the dip of a resonant are very sensitive to variations of the optical parameters of the medium on a surface-active plasmon metal layer. The sensing structures were made as follows. Gold layers were coated by means of vacuum evaporation on a substrate, 1 mm thick, made of a BK7 glass slide. The thickness of Au was about 48 nm. An active sensor layer of WO3 was deposited by thermal evaporation on the gold film while a Nafion"R" film was coated by means of the spin-coating method. The sensing structures were coupled on immersion oil with a prism coupler. A change of the intensity of light of the plasmon dip was observed when chemical active films (WO3 or Nafion"R") were exposed to varying concentrations of NH3. Optical ammonia gas sensors display a very fast response time and a fast regeneration time at room temperature.
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