Few-Layer PdSe₂ Nanofilm/Si Heterojunction for Sensing NO₂ at Room Temperature

Palladium diselenide (PdSe2), a noble transition metal dichalcogenide has attracted increasing attention in recent years due to its outstanding semiconductor properties. In this study, 2D PdSe2 nanofilms with thicknesses ranging from 2 to 28 nm and their heterostructures with Si substrates (PdSe2/Si heterostructures) were synthesized via a simple selenization method. Electrical transport characterizations based on field-effect transistor devices indicate that the few-layer PdSe2 nanofilms exhibit a p-type semiconducting behavior. The optimal sensing performance of the PdSe2/Si-8 sensor (8 nm-thick PdSe2) exhibits a comparable response toward NO2 gas (ΔR/Ra = ∼7.2% to 100 ppb and ∼18% to 1 ppm) at room temperature (RT). This response may result from the heterostructure effect and maze-type surface. Additionally, the PdSe2/Si-8 sensor has selectivity toward NO2 compared with other gases including NO, H2, CO, NH3, and C2H5OH. Furthermore, density functional theory (DFT) calculations reveal the largest adsorption energy and charge transfer between NO2 and the PdSe2 surface, which coincides well with the experimental results. Moreover, the PdSe2/Si-8 sensor also exhibits repeatability and long-term stability during about 4 months at RT. These results indicate that the PdSe2/Si heterostructures may be a promising nanomaterial for room-temperature NO2 gas-sensing devices.