Sprayed ZnO thin films for gas sensing: effect of substrate temperature, molarity and precursor solution

In this work, ZnO thin films were deposited by ultrasonic spray pyrolysis by utilizing zinc acetate and zinc nitrate as precursors. Deposition substrate temperature, solution precursor and molarity were varied. Molarity was fixed to 0.1 and 0.3 M for each precursor solution. ZnO thin films were deposited at two substrate temperatures, 250 °C and 450 °C. Morphological, structural and chemical characterizations were performed in order to study the effect of experimental conditions such as solution molarity, substrate temperature and precursor type on the ZnO thin films properties. Films deposited with acetate precursor have a polycrystalline structure, contrary to samples deposited with nitrate precursor, which are monocrystalline. Lastly, a total of eight samples with different characteristics mentioned above were utilized for CO2 detection. Our results let us suggest that sensing response is slightly higher when nitrate precursor solution is utilized. In addition, the fastest response and recovery time were found in samples deposited by nitrate precursor solution. The main objective of this work is the discussion of the increment in response and recovery time as a consequence of the electronic interaction between the CO2 and the ending (100) crystal plane of ZnO films deposited with nitrate precursor solution, which takes place due to the monodentate and bidentate adsorption path ways.