# Formation of ZnO/CuO Heterostructures Based on Quasi-One-Dimensional Nanomaterials
## 4 Synthesis of ZnO/CuO Heterostructures Based on Quasi-Dimensional Nanomaterials
Besides, the additional CuO phase leads to a decrease in the height of the potential barriers at the surface and intergranular boundaries created due to oxygen adsorption. In these conditions, the sensitivity of the sensors to such substances as acetone vapor increases, especially under backlight conditions [132]. Controlled vapor deposition [133], the co-precipitation method [134; 135], the sol-gel method [136; 137], magnetron sputtering [138], thermal oxidation [139], the hydrothermal method [140], and the solvothermal method [141] have been used to produce ZnO/CuO heterojunctions. In [142], solar cell structures based on CuO/ZnO were produced by the plasma electrolyte oxidation method. The produced heterostructures are characterized by high optical absorption in the optical range due to the appropriate band gap width of CuO, which provides strong absorption in the solar spectrum region [143]. The application of active layers in the form of nanowires and nanorods, which increase the transition area and improve the accumulation of charge carriers, is considered a promising way to increase the efficiency of solar cells based on CuO/ZnO heterojunctions [144]. In [145], it has been shown that bulk heterojunctions in ZnO/CuO-based solar cells are not considered in the literature. Figure 6: X-ray diffraction (XRD) pattern of samples from CuO, ZnO and CuO/ZnO heterostructure synthesized by microwave-assisted hydrothermal method [125]. Figure 7: High-resolution transmission electron microscopy image the ZnO/CuO heterostructure: CuO particles are loaded on the surface of ZnO (**a**). A magnified view of the enclosed regions: The interface between ZnO and CuO particles is represented by a red dotted line (**b**). Fast Fourier transform (FFT) (**c**). Transmission electron microscopy image the ZnO/CuO heterostructure having a diameter of 1.00–1.21 μm and a height of 1.99–2.30 μm (**d**) [130]. cells can be formed using one-dimensional ZnO nano-objects, and no ordering of arrays of such nano-objects is required. Zinc oxide has n-type conductivity, while the formation of a p-type conductivity layer is achieved by the deposition of copper oxide. CuO fills the space between the one-dimensional zinc oxide objects, creating contact with the current-carrying electrode. The main methods for creating one-dimensional nanostructures are gas-phase deposition, in which nanocrystals grow by the vapour-liquid-crystal mechanism, liquid-phase methods, and template synthesis. Gas-phase methods of physical or chemical deposition are widely used for the synthesis of quasi-one-dimensional zinc oxide nanostructures. In this method, not only the synthesis conditions but also the specific geometry, internal tooling and other parameters of the reactor used are factors that have a strong effect on the morphology and properties of the grown ZnO nanostructures [146]. Among the liquid-phase methods of producing ZnO nanostructures are hydrothermal, using water as a solvent, solvothermal, based on the use of non-aqueous solvents, and the electrodeposition method. In general, the morphology of deposited ZnO nanostructures depends on the thickness of the seed layer and the properties of the substrate used. That is, growth mechanisms are influenced by many factors, so even small changes in synthesis conditions may lead to significant modifications in the morphology and properties of the created nanomaterials [147]. Thus, the development of reliable methods for the production of nanomaterials and heterostructures remains a topical issue. In [148; 149; 150; 151] new method of pulse periodic laser irradiation has been developed and a range of nanomaterials from nanoporous to layered based on ZnO nanowires have been synthesized. It was defined that a non-stationary stress-strain state caused by laser-induced vibrations is a condition for the intensification of mass transfer in the solid phase of metallic materials to be treated.