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.