Revealing the relationship of NO2 sensing with energy level in 2D van der Waals SnS1-xSex alloys

Understanding the relationship between sensing behavior and energy level is an important prerequisite for providing rational guidance to predict advanced gas-sensing materials and develop design principles. A tunably compositional van der Waals (vdW) alloy SnS1-xSex (x=0.2, 0.4, 0.6, 0.8) that reveals the trend of response value with Fermi level is first reported here, which is prepared by the isoelectronic Se atoms substituting the S atoms of SnS via an ion exchange method. The cause-and-effect of the energy level with response value is disclosed by Kelvin probe force microscopy, which reveals that increasing the gap between the Fermi level of alloys and the molecular orbital of NO2 by tuning Se content can enhance the response value for NO2. Compared to a no response to NO2 for pristine SnS crystals at room temperature, the as-prepared SnS1-xSex vdW alloys show a sensitive p-type response, in which the response value reaches 400.3% for SnS0.6Se0.4 alloys toward 20 ppm NO2 with a short response/recovery time (80 s/140 s). The SnS0.6Se0.4 alloys also have excellent selectivity and good stability. As a basic and crucial step, this work could pave the way to develop the gas sensors of vdW layered crystals with a p-type high-sensitive response, and also could be extended to electronics, sensing, and catalysis fields.