ZnO and SnO 2 are two important wide bandgap semiconductor materials, which have applications in many fields. [1][2][3][4][5][6] In order to tailor the properties of ZnO and SnO 2 , Sn-doped ZnO and Zn-doped SnO 2 have been studied. [7][8][9][10] Recently, nanocomposites composed of ZnO and SnO 2 and ternary compounds composed of Zn, Sn, and O have also attracted wide attention from scholars and engineers in different fields. For instance, Lee et al. [11] used pulsed laser deposition to prepare ZnO-SnO 2 composite films; those composite films were amorphous after annealed at 300 C but had good photoelectric properties and could be used to prepare high-quality field effect transistors. T. Tharsika et al. [12] used spray pyrolysis technique to prepare a ZnO-SnO 2 composite film and found that the morphology of the sample was controlled by the heat treatment and the Zn:Sn ratio in the growth solution. Yan et al. [13] prepared ZnO/ZnSnO 3 composites by hydrothermal method and found that those composites had better gas sensitivity than pure ZnSnO 3 . Zheng et al. [14] synthesized a ZnO-SnO 2 nanocomposite through a two-step route and found that the sensor prepared from the composite material showed better gas sensitivity to chlorine than the sensor prepared from pure SnO 2 . The ZnO-SnO 2 nanocomposites and ternary compounds composed of Zn, Sn, and O have attracted great attention from researchers worldwide because they have potential applications in field effect transistors, [11] solar cells, [14,15] thin-film transistors, [16] gas sensors, [17,18] photocatalysts, [19] and other fields.As we all know, the preparation methods and deposition parameters of nanomaterials have a large influence on the properties of nanomaterials. For ZnSnO nanomaterials, the impact of different preparation methods is particularly obvious. Normally, the ZnSnO films obtained by the physical vapor method show smooth surface and uniform grains. [11,13] However, ZnSnO thin films deposited by the wet chemical method show higher controllability of morphology and optoelectronic properties. [20,21] For instance, Tharsika et al. [20] fabricated ZnO-SnO 2 composite films by spray pyrolysis; the microstructure and optical properties of the ZnO-SnO 2 films were not only related to the atomic ratio of Zn to Sn in growth solution, but also related to the heat-treatment temperature. The ZnO-SnO 2 composite film heat-treated at an appropriate temperature showed a double-layered structure: The bottom layer was an amorphous Zn x Sn y O z compound, and the upper layer was made up by many rod-like or sheet-like ZnO nanostructures. The sol-gel process is an attractive way for preparing metal oxide nanofilms and is particularly suitable for preparing multicomponent metal oxide films. To our knowledge, up to present, there is no paper to report a two-layered film composed of crystalline ZnO and amorphous Zn x Sn y O z compound deposited using the sol-gel technique. In this research, the authors have prepared ZnSnO thin films with unique microstructure and optica...
