# Formation of ZnO/CuO Heterostructures Based on Quasi-One-Dimensional Nanomaterials
## 4 Synthesis of ZnO/CuO Heterostructures Based on Quasi-Dimensional Nanomaterials
A significant increase (at least 200%-300% compared to plain exposure to laser beam heating) in the diffusion coefficient in a metallic material was described [152]. The use of this identified synergistic effect of heat exposure and laser-induced vibrations made it possible to create semiconductor nanostructures on a metal substrate, including a composite material consisting of zinc oxide nanowires and copper oxide nanofilms. The formation of a crystalline structure of these semiconductors that have different conductivity types determines the creation of n-ZnO/p-CuO anisotropic heterojunction between them [38]. To create a ZnO/CuO heterostructure based on ZnO nanowires, pulsed-periodic laser irradiation on the pre-etching surface of Cu-Zn alloy has been proposed. Dezincification by etching created an alloy surface consisting of separate micrograin surfaces with high Cu content and their surrounding grain boundaries. The laser irradiation was carried out with a pulse frequency of 100 Hz; the laser power was 330 W and the diameter of the laser spot on the surface of the samples was 16 mm [38]. After such pulsed-period exposure, ZnO nanowires predominated in the grain boundary area, while the surface of each micrograin was coated with a CuO nanofilm, forming a ZnO nanowire/CuO nanofilm composite material. Figure 8 shows a photo of the setup that has been used to study the vibration characteristics of the samples during the laser-induced formation of nanopores and nanowires [152]. Figure 9 shows a graph of the averaged over the sample surface vibration rate as a function of the sample vibration frequency during laser irradiation at a frequency of 100 Hz. Figure 10 illustrates the vibration rate distribution over the sample at a frequency equal to the laser irradiation frequency of 100 Hz. Figure 11 shows a scanning electron microscopy image of ZnO nanowires formed on the surface of Cu-Zn alloy during laser irradiation of a previously etched material [38]. It was established that the products of thermal oxidation during pulse-periodic laser irradiation are different and depend on the initial surface composition. When laser exposure was performed on a non-etching material, ZnO nanowires were formed on the porous metallic material. After surface dezincification, a composite material consisting of a network of ZnO nanowires and a CuO nanofilm on the surface of the metal material was formed by laser exposure. Figure 8: Photo of the setup used to study the vibration characteristics of the samples: 1—pulse-periodic laser; 2—three-coordinate scanning laser vibrometer; 3—mirror of optical system; 4—two-coordinate scanning laser vibrometer; 5—non-contact thermometer; 6—Cu-Zn alloy sample [152]. Figure 10: _Cont._  
Figure 9: Graph of the averaged over the sample surface vibration rate as a function of the sample vibration frequency during laser irradiation at a frequency of 100 Hz [38]. During experimental studies described in [153], the pulse frequency was adjusted in the range of 10-2500 Hz. The beam power was 270-330 W and the diameter of the laser spot was 20 mm. At a beam power of 270 W, the ZnO nanowires are faintly formed on the mechanically grinded surface; when the power was increased to 330 W the density of the nanowires increased considerably. However, in this case, shorter and wider nanowires are formed. The synthesized nanowires are reinforced on a substrate and have a length of \(\sim\)0.5-3 \(\upmu\)m and a diameter of \(\sim\)40-90 nm. It has been shown that ZnO predominated in the boundary area, while CuO predominated on the remaining surface. X-ray diffraction studies of copper-zinc alloy samples with an oxide semiconductor nanocomposite synthesized on the surface were carried out. Analysis of X-ray diffraction patterns showed that pulse-periodic laser irradiation leads to the formation of monoclinic CuO (a = 4.6853 A, b = 3.4257 A, c = 5.1303 A, \(\beta\) = 99.549\({}^{\circ}\)) and wurtztze ZnO (a = 3.24982 A, b = 3.24982 A c = 5.20661 A) on the porous Cu-Zn alloy substrate (a = 4.256 A).