Investigation of the electrical and ethanol-vapour sensing properties of the junctions based on ZnO nanostructured thin film doped with copper

We present the investigation of ethanol sensing properties of the junctions composed by two plane-parallel nanostructured thin film electrodes. One of them consists of pure ZnO and the other one is composed of ZnO doped with Cu. The thickness of the lower layer was kept constant for all of the investigated structures. The thickness of the upper layer was varied. The samples were produced with different thickness of the top layer by changing the numbers of dip-coatings cycles. On produced junction structures we investigate the dependence of the potential difference on the temperature in the air flow and the changes that occur under exposure to flow of air with certain concentration of ethanol vapour. For ZnO/ZnO:Cu junction with top layer produced by two dip-coatings cycles, the potential difference under the air flow were getting more positive values up to 290 °C and then the values were decreasing, while for ZnO/ZnO:Cu junction with top layer produced by three dip-coatings cycles, the potential difference were getting more negative values with increasing the temperature. However in both cases the potential difference increases in value, when the structures are exposed to the vapour of ethanol. On this installation by the exchange the content of gas atmosphere at fixed temperature the ethanol concentration dependence of the potential difference of produced junction structures were evaluated. Both samples have shown nonlinear dependence of signal towards the concentration of ethanol vapour. The observed results for ZnO/ZnO:Cu were compared with those of the junctions composed by layers of ZnO doped with Ga and pure ZnO nanowires. The performed fractal analysis based on the SEM images showed a correlation between the fractal dimension of the surface of the upper layer of the samples and gas-sensitive properties of the sensing structures.