Highly sensitive and selective ammonia (NH3) sensing by annealed pulse laser deposited (PLD) - ZnO thin films

This work reports highly sensitive and selective ammonia (NH₃) gas sensor development with a detection limit 5.2 ppm achieved by PLD-deposited ZnO thin film, annealed at 450 °C. At this annealing temperature, ZnO film exhibited a very high sensing response of 89 % on exposure to lowest NH₃ concentration at 300 °C operating temperature. Moreover, a fast response time of 60 s and a recovery time of 65 s are recorded. Comparatively, the sensor response is 9 times higher (89 %) than the response obtained by unannealed ZnO thin film (10 %) for the same gas concentration. Additionally, the optimized film exhibits excellent selective detection towards NH₃ gas as compared to other interfering gases (CO, H₂, CO₂, O₂, NO₂, C₃H₆O, C₂H₂, and CH₄). Also, the sensor’s repeatability is examined over a multiple number of gas exposure cycles, and good stability is achieved. The physical properties of PLD-deposited ZnO films are systemically explored by using X-ray diffraction (XRD), Atomic force microscopy (AFM), Field emission scanning electron microscope ( FESEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) techniques, and electrical I-V measurement. The conducive performances of ZnO thin film annealed at 450 °C indicate a strong candidate for the detection of NH₃ gas. Based on ultra-low detection limit and quantification ability under mixed gases exposure, annealed ZnO film exhibits a promising candidate for real-time exhaled breath NH₃ monitoring for the identification of disease biomarkers like liver and kidney diagnosis application.