# Creation of One- and Two-Dimensional Copper and Zinc Oxides Semiconductor Structures
## 2 Formation of One- and Two-Dimensional ZnO and CuO Structures  
The formation of one- and two-dimensional zinc oxide structures can be performed by various methods based on chemical, physical and combined approaches. A common method is the hydrothermal method, which involves a reaction between a solution and a zinc precursor at high temperature and pressure in a closed vessel [48; 49; 50]. The process can promote the growth of ZnO nanowires, nanorods, or nanobelts, resulting in quasi-one-dimensional structures. The sol-gel spin coating method can be used in the preliminary step of the fabrication of such structures to deposit high-density and homogeneous seed layers of ZnO nanoparticles on the active surface of the substrate. In the final step, the hydrothermal method is used to grow arrays of ZnO nanowires or nanorods. Figure 1 shows a schematic diagram of the fabrication of a ZnO quasi-one-dimensional structure in two steps [51]. Scanning electron microscope (SEM) images of a substrate, the seed layer, and ZnO nanowires are presented in Figure 2[52]. Figure 1: Schematic diagram of the fabrication of a ZnO quasi-one-dimensional structure in two steps: (**a**) Sol–gel spin coating and (**b**) hydrothermal method [51]. Hydrothermal synthesis is also used for the fabrication of two-dimensional materials like oxide nanosheets. It allows one to precisely control the size, morphology, and crystal structure of the nanosheets [52]. Images of porous ZnO nanosheets produced by the hydrothermal synthesis method are presented in Figure 3[53]. The method has been widely used in nanotechnology to create structures for various applications including catalysts, photodeactivators, sensors, and energy storage devices [54; 55; 56] as it has advantages such as ease of integration and control of the structure length [57]. However, it has disadvantages such as a longer growth period and reduced quality of the synthesized crystals. In addition, the arrangement of zinc oxide nanostructures produced using this method is closely related to the preferred orientation of the seed-layer crystals [58]. Figure 3: SEM images of porous ZnO nanosheets produced by the hydrothermal synthesis method [53]. Figure 2: Scanning electron microscope (SEM) image from a top view showing (**a**) a fluorine-doped tin oxide-coated substrate and (**b**) a seed layer. (**c**) Cross-sectional SEM image illustrating the ZnO nanowires that have been grown. All scale bars in the images represent a length of 0.5 μm [52]. Among various methods available for producing ZnO nanostructures, chemical bath deposition (CBD) has garnered considerable interest due to its simplicity, cost effectiveness, suitability for large-scale production, and low-temperature operation [59; 60; 61]. Chemical bath deposition involves the chemical precipitation of ZnO from a solution by controlling chemical reactions and pH [62; 63; 64]. It can be used to create thin films, nanoparticles, and nanocrystals of ZnO. The growth of high-quality ZnO nanomaterials along specific orientations remains a current and important topic. In this context, the production of ZnO nanomaterials showing a predetermined orientation has been demonstrated. In [65], the electrospun ZnO fibers were employed as seed templates to generate ZnO crystals with varying orientations. In [66], the growth of nanomaterials, in this case, nanorods, in the plane of the preferred crystal orientation of ZnO seed-layer films deposited by the sol-gel method has also been observed, meaning that the positioning of zinc oxide nanostructures obtained by this method is also associated with the preferred orientation of the crystals in the seed layer. For the fabrication of two-dimensional materials, the sol-gel synthesis method is significant, offering advantages over high-temperature processing [67; 68]. In high-temperature methods, materials may undergo phase changes, crystal growth, or unwanted reactions that can alter their characteristics.