Robust Room-Temperature NO₂ Sensors from Exfoliated 2D Few-Layered CVD-Grown Bulk Tungsten Di-selenide (2H-WSe₂)

We report a facile and robust room-temperature NO₂ sensor fabricated using bi- and multi-layered 2H variant of tungsten di-selenide (2H-WSe₂) nanosheets, exhibiting high sensing characteristics. A simple liquid-assisted exfoliation of 2H-WSe₂, prepared using ambient pressure chemical vapor deposition, allows smooth integration of these nanosheets on transducers. Three sensor batches are fabricated by modulating the total number of layers (L) obtained from the total number of droplets from a homogeneous 2H-WSe₂ dispersion, such as ∼2L, ∼5-6L, and ∼13-17L, respectively. The gas-sensing attributes of 2H-WSe₂ nanosheets are investigated thoroughly. Room temperature (RT) experiments show that these devices are specifically tailored for NO₂ detection. 2L WSe₂ nanosheets deliver the best rapid response compared to ∼5-6L or ∼13-17L. The response of 2L WSe₂ at RT is 250, 328, and 361% to 2, 4, and 6 ppm NO₂, respectively. The sensor showed nearly the same response toward low NO₂ concentration even after 9 months of testing, confirming its remarkable long-term stability. A selectivity study, performed at three working temperatures (RT, 100, and 150 °C), shows high selectivity at 150 and 100 °C. Full selectivity toward NO₂ at RT confirms that 2H-WSe₂ nanosheet-based sensors are ideal candidates for NO₂ gas detection.