Room-Temperature NO₂ Sensing of CVD-Modified WS₂-WSe₂ Heterojunctions

Two-dimensional (2D) semiconducting heterojunction chemical sensors are in high demand because of their enhanced response, stability, and selectivity. However, fine-tuning heterojunctions using vapor deposition growth still needs further research. Our present study focuses on the ambient pressure chemical vapor deposition (CVD) synthesis of hexagonal tungsten sulfide-tungsten selenide (WS₂-WSe₂) p-p heterojunctions (as a 2D-2D arrangement). We use the liquid-phase exfoliation method to disperse bulk WS₂ and WSe₂ and decorate large flakes of WS₂ with smaller WSe₂ nanosheets in CVD. Electron microscopy and related surface investigations reveal their homogeneity on drop-casting. Two drops from the exfoliated heterojunction dispersion were drop-cast on a transducer to study the NO₂ response and related sensing properties. The sensor showed long-term stability (>2 months), even at high humidity levels (40-90%). The gas-sensing properties of this layered p-p heterojunction-based nanocomposite strongly suggest an affinity toward NO₂ gas, leading to improved response, high stability, independent of humidity effects, and high selectivity.