Development of flexible paper substrate sensor based on 2D WS2 with S defects for room-temperature NH3 gas sensing

For the important applications of gas identification related to specific diseases in healthcare, flexible gas sensors have attracted more attention. Among them, two-dimensional transition metal dichalcogenides (2D TMDs) have been known as good promising flexible gas-sensitive materials. While how to tightly attach 2D materials on flexible substrates is still challenging. Here, we propose an enhanced room-temperature flexible paper-substrate sensors based on 2D tungsten disulfide (WS2) with S defects, which are facilely synthesized by chemical exfoliation and vacuum filtration method. Structure characterization shows that most of the as-prepared 2D WS2 are within 3 layers. Spectroscopic characterization proves the existence of S defects on the surface of 2D WS2 produced by chemical exfoliation. The room-temperature (25 degrees C) NH3 gas sensitivity results show that the response intensity of 2D WS2 with rich S defects is nearly three times higher than the highly crystalline 2D WS2. The results of the flexible gas sensitivity indicate the fast response and high stability of our devices in breathing detection and bending experiments. Furthermore, the devices can effectively distinguish bending stress changes and gas-sensitive response signals at the same time, realizing multifunctional sensing detection. Our work will be a reference for fabricating flexible sensors based on 2D materials.