Theoretical and experimental investigations of ethanol vapour sensitive properties of junctions composed from produced by sol–gel technology pure and Fe modified nanostructured ZnO thin films

Nanosized thin films of pure and Fe modified ZnO are used to construct the composed by two plane-parallel nanostructured thin film electrodes sensing junctions. The lower and upper layers overlap is kept ∼80 mm2 for all of the investigated samples. The samples are produced with different thickness of the Fe doped top sensing layer by changing the numbers of dip-coatings. The investigations of the temperature dependence of the potential difference of produced junctions and their changes under exposure to ethanol vapour with certain concentration are made by means of a newly constructed experimental setup. These investigations are performed in the temperature range of 180–350 °C in environment of pure air and at fixed temperature sample is exposed to certain concentration of ethanol vapour. The best sensing performance is obtained for the structure with upper layer produced by two dip-coatings in the sol containing 3 at.% of Fe into it. For explanation of observed nonlinearity of sensor response towards ethanol vapour concentration as well as change in polarity of the potential difference with modifying the morphology of Fe doped working layer of the gas sensing junction, the theoretical model of operation of produced sensing junctions is developed. This model provides the possibility of prediction of gas-sensing properties of ZnO/ZnO:Fe junction structures depending on concentration of electrons into the composing junction layers. It is worthy to mention that the model is applicable for prediction of suitability of this kind for sensing structures to detect many gasses, which is very important for the researchers, working in the field of gas-detection.