Influence of Layers Morphology on the Sensitivity of SnO2-based Optical Fiber Sensors

Recently, the capability of a SnO₂ based silica optical fiber (SOF) sensors to detect ammonia at room temperature in water environment has been for the first time demonstrated [1-3]. The SOF probes were deposited onto the fiber end by the simple and low cost Electrostatic Spray Pyrolysis technique (ESP), which allows to change the layers features by changing the deposition parameters. Here, it is experimentally demonstrated that modifications of the optical near field behavior occur when the sensitive overlay exhibits peaks with dimensions comparable with the light wavelength (1.55 mum). In addition, the influence of the SnO₂ layers morphology on the room temperature sensing performances against ammonia, in water environment, is preliminarily investigated. To the aim, before performing the ammonia adsorption measurements, the topography and the optical near field profile for different SnO₂-based sensors have been analyzed by a very complex instrumentation able to perform simultaneous atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) imaging.