Investigation of ZnO thin-film sensing properties for CO2 detection: effect of Mn doping

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-Ka 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.