Sensing Properties and Mechanism of Gas Sensors Based on Zinc Oxide Quantum Dots

In this article, the quantum dots were employed to prepare gas sensing films, whose grain size was controlled up-to twice the Debye length, which is beneficial to investigate the grain size effect within a certain range, on the sensing mechanism and sensing mechanism of the gas sensors, as Debye length is strongly related to barriers of grain boundaries. In order to clarify the relationship of gas sensing mechanism to grain size and Debye length, the grain size of ZnO films were controlled by heating conditions like reaction temperature and reaction time of Zn(OAc)2 and LiOH, while the Debye length was influenced by operating temperature. The sensing ability of ZnO films with different grain sizes were analyzed under different conditions, when employed to H2S gas. Interestingly, the best sensitivity were observed for grain size much closer to two times of the Debye length. In order to investigate this phenomenon, a Debye model of grain size effects has been derived based on the basic chemical reactions between H2S and absorbed oxygen ions on surfaces of ZnO grains. It indicated that the gas sensitivity would reach the highest sensitivity when the grain size is twice the Debye length, which is in full agreement with experiment's results.