Understanding the chemical reception and electronic transduction mechanism in gas sensing with sulfide colloidal quantum dots

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Today, there is a need for low-cost and highly efficient sensors to detect low concentrations (ppb level) of toxic gases. Currently, traditional chemiresistive sensors based on semiconducting oxides (SMOX) are widely used due to their excellent sensor responses, robustness and low cost. SMOX based sensors, however, require high operation temperatures between 200 °C and 600 °C resulting in both high power consumption and safety issues. As a result, there is a worldwide effort to produce rapid, sensitive, low temperature-operating gas sensors. Metal sulfides are emerging as promising materials. At room temperature, sensors based on PbS show high responses to NO2 and NH3, while ZnS is known to show a high response to H2S. For even better results, a new development is the use of sulfide colloidal quantum dots (CQDs) for gas sensing. CQDs have an extremely large surface-to-volume ratio capable of active interaction with target gas molecules. In addition, the size controlled synthesis of sulfide CQDs allows electronic and optical properties to be changed. The goal of this project is to understand the chemical reception of sulfide CQDs. The results of other metal sulfides, e.g. Bi2S3, SnS, and ZnS will be compared to those for PbS. The surface reaction mechanisms and possible sources of instability will be identified using operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Operando work function measurements will provide insight into the charge transfer processes associated with the surface chemistry. The results will provide the input for a sensing model. This model will serve as a basis for understanding gas sensing with metal sulfides.