CVD growth of self-assembled 2D and 1D WS2 nanomaterials for the ultrasensitive detection of NO2

Herein, we report for the first time on the facile synthesis of 2D layered WS2 nanosheets assembled on 1D WS2 nanostructures by combining the aerosol assisted chemical vapor deposition (AA-CVD) method with H2-free atmospheric pressure CVD, for an ultrasensitive detection of NO2. This synthesis strategy allows us a direct integration of the sensing material onto the sensor transducer with high growth yield and uniform coverage. Two different WS2 morphologies (nanotriangles and nanoflakes) were prepared and investigated. The results show that the assembly of layered WS2 nanosheets on a 3D architecture leads to an improvement in sensing performance by maintaining a high surface area in an accessible porous network. The sensors fabricated show stable, reproducible and remarkable responses towards NO2 at ppb concentration levels. The highest sensitivity was recorded for WS2 NT sensors, with an unprecedented ultra-low detection limit under 5 ppb. Additionally, this material has demonstrated its ability to detect 800 ppb of NO2 even when operated at room temperature (25ºC). Regarding humidity cross-sensitivity, our WS2 sensors remain stable and functional for detecting NO2 at ppb levels (i.e., a moderate response decrease is observed) when ambient humidity is raised to 50 %. An 8-month long-term stability study has been conducted, which indicates that WS2-NT sensors show a very stable response to NO2 over time.