Notable synthesis, properties and chemical gas sensing trends on molybdenum disulphides and diselenides two-dimensional nanostructures: A critical review.

Evaluation of synthesis methods, notable properties, and chemical gas sensing properties of molybdenum disulphides and diselenides two-dimensional nanosheets is unfold. This is motivated by the fact that the two dichalcogenides have good sensitivity and selectivity to different harmful gases at ambient temperatures. Synthesis methods explored include exceptional top-down and bottom-up approaches, which consider physical and chemical compositional inceptions. Mechanical exfoliation in both molybdenum disulphides and diselenides nanosheets demonstrate good crystalline purity with structural alterations under varying stacking conditions. These chalcogenides exhibit low energy band gaps of ±1.80 eV for MoS and ±1.60 eV for MoSe, which reduces with introduction of impurities. Thus, upon doping with other metal elements, a transformation from either n-type or p-type semiconductors is normally observed, leading to tuneable electronic properties. Thus, different gases such as methane, ethanol, toluene, ammonia, nitrogen oxide have been systematically detected using molybdenum disulphide and diselenide based thin films as sensing platforms. This review highlights structural, electronic and morphological characteristics of the two dichalcogenides which influences the sensitivity and selectivity ability for a couple of gases at ambient temperatures. The strategies for enhancing the selectivity by introducing defects, impurities and interfacing with other composites expanding the choice of these gases wider is also discussed in details. The review also provides overviews of challenges and limitations that open new research avenues to further enriching both chalcogenides as flexible, stable and cost effective state-of-the-art chemical gas sensors.