Study of Metal-sulfide Chemoresistive Properties for Gas Sensing

Although the electrical, optical, structural and morphological features of metal sulfides have been widely investigated, such materials lack of investigation for gas sensing applications. We propose metal sulfides as a novel class of sensing materials. Potentially, metal sulfides may be of interest because they can circumvent the problem of in/out diffusion of oxygen vacancies, which in turn leads to long-term instability. Cadmium Sulfide and Tin (IV) Sulfide were investigated as functional materials as chemoresistive gas sensors. Films were deposited by screen-printing and electrical characterization was carried out under either thermo- or photo-activation mode. In thermo-activation mode, these materials showed high selectivity to aldehydes and ketones (SnS2) and alcohols (CdS), as well as good stability and sensitivity. In this condition of activation, a comparison between metal sulfides and their metal-oxides counterparts was carried out, revealing larger selectivity to specific analytes and significant long-term stability for the sulfides. Moreover, due to a looser bond of sulfur than oxygen, the activation temperature for reversible operation of the sensors was lower for the sulfides than for the oxides. The sensing properties in photo-activation mode highlighted good chemoresistive properties of CdS with tested gases, in particular as the radiation wavelengths approach the band gap energy.