Integration of ZnO nanowires with coupled resonators for ammonia gas detection

This study presents a novel ammonia sensor using hydro-thermally synthesized ZnO nanowires integrated with a mode-localized coupled resonator. The ZnO nanowires, with their high sur-face area, act as an efficient gas adsorption layer. The resonator’s driving mechanism was optimized using finite element method (FEM) simulations, revealing that a coupled resonator pair exhibited 45.52 times higher sensitivity than a single resonator. Out-of-phase modes showed greater sensitivity than in-phase modes. Resonators R1 and R2 driven together had the lowest sensitivity, while Resonator 1, with a zinc oxide layer and driven individually, demonstrated the highest sensitivity. Additionally, the sensitivity of the coupled resonator in-creased with the decrease in DC bias voltage. Comprehensive mate-rials characterization of the ZnO nanowires was conducted using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) to confirm their structural and chemical properties. Fourier-transform infrared spectroscopy (FTIR) results showed that after ammonia adsorption, zinc oxide nanowires exhibited additional absorption bands at approximately 1430 cm−1, 1633 cm−1, and within the broad range of 3100 to 3550 cm−1. The sensor’s gas-sensing performance was evaluated with varying ammonia concentrations, achieving a very high sensitivity of 0.0026 ppm−1 in the 25–100 ppm range at room temperature. This design highlights the potential of integrating ZnO nanowires with modal-coupled resonators for highly sensitive, miniaturized, low-cost sensors for environmental monitoring and safety applications.