Zinc oxide is a promising multifunctional material. The practical use of nano- and polycrystalline ZnO devices faces a serious problem of instability of electrical and luminescent characteristics, due to the adsorption of oxygen by the surface during aging. In this paper, the aging effect in ZnO films and nanorod arrays was studied. It was found that ZnO samples demonstrate different behavior of the degradation process, which corresponds to at least two different types of adsorbing surface sites for O2, where O2 adsorption is of a different nature. The first type of surface sites is rapidly depassivated after hydrogen passivation and the aging effect takes place due to these centers. The second type of surface sites has a stable structure after hydrogen passivation and corresponds to HO–ZnO sites. The XPS components of these sites include the Zn2p3/2 peak at 1022.2 ± 0.2 eV and Zn2p1/2 peak at 1045.2 ± 0.2 eV, with a part of the XPS O1s peak at 531.5 ± 0.3 eV. The annealing transforms the first type of site into the second one, and the subsequent short-term plasma treatment in hydrogen results in steady passivation, where the degradation of characteristics is practically reduced to zero.

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Nanocrystalline cobalt oxide Co3O4 and the ZnO / Co3O4 composite were obtained by the chemical bath deposition method followed by thermal annealing. It has been shown that the growth mechanism of cobalt carbonates changes dramatically in the presence of zinc oxide particles during synthesis, as a result, the phase composition, morphology, and material properties change. The conductive layers formed from the ZnO / Co3O4 composite have an electrical resistance at room temperature that is more than three orders of magnitude lower than the resistance of the Co3O4 layers, and ZnO / Co3O4 composite gas sensors showed significantly higher gas sensitivity at room temperature than that of control cobalt oxide sensors.