Thermal annealing induced mazy structure on MoO₃ thin films and their high sensing performance to NO gas at room temperature

MoS₂ thin films were prepared by radio frequency (RF) magnetron sputtering and then annealed in air. X-ray diffraction (XRD), field-emission electron scanning microscopy (FESEM) and transmission electron microscopy (TEM) were adopted to characterize the phase structure and surface morphology. Interestingly, upon thermal annealing in air, MoS₂ thin films changed into α-MoO₃ with mazy morphology, and the thin films were covered by MoO₃ nano-sheets with a length of 30–50 nm and a width of 10 nm. α-MoO₃ thin films with mazy morphology showed excellent response to NO gas at room temperature. The response of 5% and 92% was obtained at 5 ppm and 200 ppm, respectively, and the response and recovery times were 30 s and 1500 s. Moreover, the mazy structure of MoO₃ exhibited good selectivity to NO gas with respect to SO₂, NH₃ and H₂ gases. The high surface-to-volume ratio was the dominant factor for high sensing performance.