# Creation of One- and Two-Dimensional Copper and Zinc Oxides Semiconductor Structures
## 2 Formation of One- and Two-Dimensional ZnO and CuO Structures
In contrast, sol-gel synthesis typically takes place at lower temperatures, often at room temperature or slightly elevated temperatures, which decreases the likelihood of such changes occurring. The preparation principle of sol-gel synthesis involves the conversion of a sol (a colloidal suspension of nanoparticles) into a gel (a three-dimensional network of interconnected nanoparticles) and then into a solid material. This process is typically achieved through the hydrolysis and condensation of precursor molecules. The key to successful preparation lies in the precise control of the synthesis conditions, allowing us to achieve the desired properties in the final products. By precisely controlling the reaction conditions, such as the choice of pre-cursors, solvent, pH, and temperature, the properties of the resulting two-dimensional materials can be tailored [69]. The most commonly used methods to create one-dimensional ZnO structures such as nanowires, nanorods, or nanotubes are hydrothermal synthesis, chemical bath deposition (CBD), and other approaches that facilitate the growth of structures in one dimension. Figure 4 shows a schema of a two-step process of the fabrication of ZnO nanorods, which contains the sol-gel process and subsequent hydrothermal synthesis [70]. The sol-gel method may be also incorporated into subsequent processing steps for surface coatings or functionalization of one-dimensional ZnO structures [71], but in most cases, it is not the primary method for their synthesis. For the fabrication of one- and two-dimensional zinc oxide structures, one method that is used is spray pyrolysis [72; 73]. It involves the formation of spray droplets containing precursor compounds, which are then subjected to high-temperature pyrolysis. This process can be used to produce ZnO thin films, as well as nanowires, nanorods, or nanotubes, which are one-dimensional structures [74]. Spray pyrolysis allows for precise control over the morphology and size of the resulting ZnO nanostructures and is employed in nanotechnology research [75]. The atomic layer deposition (ALD) technique is also used to fabricate two-dimensional zinc oxide-based structures. ALD enables the deposition of thin ZnO films with atomic precision by sequentially depositing one atomic layer at a time. It can be used to create 2D structures such as thin films and nanolayers [76; 77; 78]. Thermionic vacuum arc (TVA) deposition is also applied, which allows for the growth of thin ZnO films and layers on substrates by physical vapor deposition using an anodic vacuum arc. This method can be applied to create single-layer and multilayer 2D structures [79; 80]. Also, molecular beam epitaxy (MBE) [81; 82; 83] and chemical vapor deposition (CVD) [84; 85; 86] methods provide sufficient structural quality and can be used to create a variety of 2D structures. These methods involve the growth of ZnO crystals on substrates at high temperatures and in a vacuum, whereby using chemical vapor deposition one-dimensional structures can be obtained [87]. The choice of method depends on the specific requirementsof research or application, as well as the desired structural and electronic characteristics of the ZnO material. The method of hydrothermal synthesis, in which copper precursors react with oxygen in an aqueous solution at elevated temperatures and pressures, is used to fabricate 1D and 2D copper oxide (CuO) structures [88; 89]. This method can yield 1D structures like CuO nanowires or nanorods, as well as 2D structures of divalent copper oxide and ZnO-CuO nanocomposites [90; 91; 92]. To create one-dimensional structures on the surface, chemical vapor deposition (CVD) can be used. This method involves the chemical reaction of gaseous copper precursors at high temperatures for the deposition of CuO on a substrate [93]. Other physical vapor-deposition techniques (PVD), such as magnetron sputtering, thermal evaporation, thermal oxidation, and molecular-beam epitaxial (MBE) growth, are applied.