WS₂ and MoS₂ thin film gas sensors with high response to NH₃ in air at low temperature

Transition metal dichalcogenides (TMDs) have received immense research interest in particular for their outstanding electrochemical and optoelectrical properties. Lately, chemical gas sensor applications of TMDs have been recognized as well owing to the low operating temperatures of devices, which is a great advantage over conventional metal oxide based sensors. In this work, we elaborate on the gas sensing properties of WS₂ and MoS₂ thin films made by simple and straightforward thermal sulfurization of sputter deposited metal films on silicon chips. The sensor response to H₂, H₂S, CO and NH₃ analytes in air at 30 °C has been assessed and both MoS₂ and WS₂ were found to have an excellent selectivity to NH₃ with a particularly high sensitivity of 0.10 ± 0.02 ppm⁻¹ at sub-ppm concentrations in the case of WS₂. The sensing behavior is explained on the bases of gas adsorption energies as well as carrier (hole) localization induced by the surface adsorbed moieties having reductive nature.