Light-Enhanced CdS Quantum Dot and Cicada-Like Fe2O3 Collaboratively Induce Band-Level Discretization and Trap-State Charge Storage for Advanced Ammonia Detection.

Metal-oxide semiconductor (MOS) gas sensors are vital for environmental monitoring, yet they face inherent trade-offs among sensitivity, selectivity, and room-temperature operation. Conventional designs rely on macroscopic interfaces rather than on a quantum-scale electronic structure. Inspired by quantum confinement, we grew CdS quantum dots on a cicada-like Fe2O3 substrate to form a planar quantum well. Quantum confinement broadens the CdS bandgap and facilitates electron transfer from Fe2O3 to CdS, where abundant defect states trap electrons, creating a stable reservoir that maintains high resistance in air. Upon ammonia exposure, trapped electrons are released, enabling high room-temperature sensitivity (68% to 100 ppm) and fast response/recovery times (17 s/43 s). The CdS quantum dots also act as a size-selective barrier, blocking larger interfering molecules while allowing NH3 to reach active sites and ensuring superior selectivity. Under photoexcitation, photogenerated electrons replenish trap states, further enhancing the response value (84.7% to 100 ppm) and selectivity (interfering with gas response below 15%). This quantum-dot-enabled charge-regulation strategy resolves long-standing trade-offs in MOS sensors and demonstrates a feasible preparation route for anchoring CdS quantum dots to cicada-like Fe2O3 scaffolds. The resulting interfacial trap-state charge storage and photoenhanced response provide a clear experimental basis for understanding the gas-sensing behavior in this specific system.