  In this study we investigated the sorption ability of Ge20Se80 thin films
applied as active layers of quartz crystal microbalance (QCM) 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 (XPS) and atom force microscopy (AFM) 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 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 200nm thick Ge20Se80
film at 5000 ppm NO2 concentration. The process of gas molecules absorption is
found irreversible at the purging conditions.
