Abstract
A simple spray pyrolysis technique has been used to fabricate ZnO/Mn thin films with different Mn concentrations (0, 5, 10 and 15 mol.%) for gas sensing applications. X-ray diffraction (with Cu-Kα radiation) patterns of the samples revealed the formation of single-phase wurtzite structure. The samples were characterized using field-emission scanning electron microscopy and scanning tunneling microscopy. The investigation revealed that the surface of pure ZnO thin film appears rougher and containing bigger grains. The response of the pure and Mn-doped ZnO thin-film gas sensors was checked at different temperatures ranging from 120 up to 200 °C, to investigate the optimum sensing efficiency. The gas sensing results have demonstrated that the pure ZnO thin film exhibited higher sensitivity to CO2 gas at 150 °C operating temperature, while the sensitivity reduced with the increase in gas pressure. Although the sensitivity of doped samples was lower than the pure sample, the sensitivity increased with the increase in pressure.
Highlights
Zinc oxide (ZnO) has given a great deal of attention due to large exciton binding energy (60 meV) and large direct band gap energy (3.37 eV) at room temperature [1,2,3]
The gas sensing results have demonstrated that the pure ZnO thin film exhibited higher sensitivity to CO2 gas at 150 °C operating temperature, while the sensitivity reduced with the increase in gas pressure
The lattice parameters of the thin films were very close, and the average crystalline size of the ZnO/Mn thin films was observed to be less than the undoped ZnO film
Summary
Zinc oxide (ZnO) has given a great deal of attention due to large exciton binding energy (60 meV) and large direct band gap energy (3.37 eV) at room temperature [1,2,3]. Doping of metal oxide sensing film is a traditional technology for gas sensors. Doping ZnO with various element was used to enhance the sensing properties and reduce the operating temperature of zinc oxide-based gas sensors. Lupan et al were prepared ZnO and ZnO/Al thin films by chemical solution deposition and photo-thermal processing techniques. Their results showed that the morphological, electrical and sensing properties of zinc oxide films can be modified by controlling the growth regimes and doping concentration. Gaspera et al investigated the effect of doping with transition metal ions on the CO optical sensing properties of nanocrystalline ZnO films. Transition metal ions inside the ZnO lattice structure were found to increase the magnitude of the response and the sensitivity of the nanocomposites [26]. The doped ZnO nanorods showed the superior formaldehyde sensing property in a few second response and recovery time [27]
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