UV-assisted fluctuation-enhanced gas sensing by ink-printed MoS₂ devices

In this work, MoS₂ flakes were printed on ceramic substrates and investigated toward 1-10 ppm of nitrogen dioxide (NO₂), 2-12 ppm of ammonia (NH₃), and 2-12 ppm acetone (C₃H₆O) under UV light (275 nm). The structure of overlapping MoS₂ flakes and UV light assistance affected high responsivity to NO₂ when DC resistance was monitored, and superior sensitivity to NH₃ was obtained from the low-frequency noise spectra. MoS₂ exhibited response and recovery times in hundreds of seconds and stability throughout the experiments conducted within a few months. MoS₂ sensor exhibited a resistance drift during the detection of a specific relaxation time. Subtracting the baseline burden with exponential drift exposed the direction of changes induced by oxidizing and reducing gases and reduced DL to 80 ppb, 130 ppb, and 360 ppb for NO₂, NH₃, and C₃H₆O, respectively. The fluctuation-enhanced sensing (FES) revealed that the adsorption of NO₂ on MoS₂ decreases the noise intensity, whereas adsorbed NH₃ increases the fluctuations of current flowing through the sensor, and these changes are proportional to the concentration of gases. The noise responses for NO₂ and NH₃ were opposite and higher than DC resistance responses with subtracted baseline (an increase of 50% for 10 ppm of NO₂ and an increase of more than 600% for 12 ppm of NH₃), showing that FES is a highly sensitive tool to detect and distinguish between these two gases. This way, we introduce a simple and low-cost method of gas sensor fabrication using ink-printed MoS₂ and the possibility of enhancing its sensitivity through data processing and the FES method.