SnO2/ZnO double-layer thin films: A novel economical preparation and investigation of sensitivity and stability of double-layer gas sensors

A double-layer SnO2/ZnO gas sensor was produced by utilization of SnO2 and ZnO thin films. Top layer consisted of SnO2 produced by a sol–gel controlled-annealing technique. Bottom coating consisted of ZnO thin film precipitated by two-stage chemical deposition (TSCD) from an aqueous zinc containing solution. Both top and bottom coatings were analyzed by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and electron dispersive elemental analysis (EDAX). Auger electron spectroscopy (AES) was also used to investigate the growth of tin oxide films on zinc oxide films and their interface. Gas sensitivity of the SnO2/ZnO double layer was determined by electrical sheet resistance measurements. Although sensitivity was slightly reduced by double-layer formation, selectivity and stability were considerably improved by combination of the two thin layers. The existence of an interfacial transition layer between SnO2 and ZnO and stabilization mechanism of the SnO2/ZnO double layer were rigorously investigated in this research.