Utilizing p-type native oxide on liquid metal microdroplets for low temperature gas sensing

Highlights • Development of an amorphous p-type oxidised galinstan film confirmed by XRD and Hall effect measurements; • Sensing performance of oxidised galinstan based conductometric devices towards NO2, NH3 and CH4 at low operating temperatures up to 150 °C; • Optimal response with a more stable baseline at an operating temperature of 100 °C; Abstract Liquid metals based on gallium oxidize under ambient conditions to form a native oxide on the surface. Here we take advantage of the semiconducting properties of this oxide layer for gas sensing applications. In particular, the development of gas sensors that operate at low temperatures is an ongoing challenge. Therefore, to address this problem, we fabricated conductometric sensors based on an oxidized liquid metal galinstan layer, and investigated their sensitivity towards NO2, NH3 and CH4 gases. The fabrication of the sensing layer was achieved via a simple approach, involving the sonication of the liquid metal in acetonitrile to produce a solution of micro/nanodroplets and dropcasting it onto a non-conducting alumina substrate at different loadings. The material properties of the developed film were extensively investigated by means of field emission scanning electron microscopy, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The results confirmed the presence of an amorphous oxide on the surface of the droplets. Hall effect measurements indicated that the oxide film was p-type, which influenced the sensing response towards the different gases. We demonstrated that a physisorption process occurs at 100 °C, leading to a detection limit as low as 1 and 20 ppm for NO2 and NH3, respectively