Study of the Sorption Properties of Ge20Se80 Thin Films for NO2 Gas Sensing

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In this study we investigated the sorption ability of Ge20Se80 thin films applied as active layers of quartz crystal microbalance for NO2 gas sensing. To identify the chalcogenide system appropriate for gas sensing, we provided data for the packing fraction of a number of chalcogenide systems and discussed their suitability. We performed Raman spectroscopy, X-ray photoelectron spectroscopy and atom force microscopy measurements on the thin films both before and after gas absorption, which showed that the introduced gas molecules interact electrostatically with the chalcogen atoms of the host material and initiate some degree of structural changes in it. The weight change due to NO2 gas absorption was measured by the frequency change of the resonator. The absorbed mass increased monotonically with the thickness of chalcogenide films and the NO2 gas concentration. At the conditions of our experiment, up to 11.4 ng of the gas was absorbed into 200 nm thick Ge20Se80 film at 5000 ppm NO2 concentration. The process of gas molecules absorption is found irreversible at the purging conditions.