Abstract
In this paper, ZnO/Zn2SnO4 heterojunction films were one step fabricated by magnetron sputtering and the dependence of crystal structures, film compactness and H2 sensing properties on annealing process were investigated and discussed. The results showed that three typical surface morphologies can be controlled by adjusting annealing temperatures and periods. The films annealed at the temperature of 550 °C for 6 h showed the best H2 sensing properties. It exhibited a response (Ra/Rg) of 28.3–100 ppm H2 at the temperature of 230 °C and the detection limit is 30.2 ppb. Meanwhile, it also showed a good selectivity and long-term stability to H2. The H2 sensing mechanism is attributed to the synergistic effect between ZnO (0001) signal crystal facets and ZnO/Zn2SnO4 heterojunction structures which enhanced the gas reactivity and resistance modulation range. On the contrary, insufficient annealing restricts the film crystallinity and the growth of hexagonal ZnO while undue annealing destroys the compactness of the films, leading to poor H2 sensing properties.
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