# Creation of One- and Two-Dimensional Copper and Zinc Oxides Semiconductor Structures
## 4 Laser Thermochemical Oxidation for the Formation of ZnO and CuO-Based Nanostructures
A novel method for constructing layered composite nanomaterial structures employing zinc oxide nanowires as the basis was successfully developed. The primary focus of the study revolved around the synthesis of a metal-semiconductor ZnO/Cu nanocomposite on the surfaces of brass samples. The results demonstrated that exposing brass foils to pulse-periodic laser irradiation in the presence of air enhanced the oxidation of the surface material. This outcome was mainly attributed to the faster oxidation rate of zinc in comparison to copper, along with the diffusion of zinc towards the surface. In experimental studies, a CO\({}_{2}\) laser with radiofrequency excitation was used. Beam shaping was accomplished using an optical system that featured a diffractive optical element, as described in [153]. The pulse frequency was varied within a wide range, from 3 to 5000 Hz. In order to produce a ZnO/Cu nanocomposite with metal-semiconductor properties, pulse-periodic laser processing of the metallic material in ambient air was conducted. Laser irradiation induced a rise in temperature, primarily concentrated in the central area rather than at the periphery. The registered temperature field in the sample can be visualized in Figure 11 and the temperature distribution graph along the sample's central region in the heat-affected zone can be seen in Figure 12 [154]. The emergence of a yellowish oxide layer was observed on the brass surface. With the prolonged duration of laser treatment, the color of the coating gradually shifted towards a whitish-gray shade, which is characteristic of zinc oxide. This coating consisted of elongated crystal structures reminiscent of needle-like formations. To analyze the elemental composition of this coating, an electron-probe energy dispersive microanalysis system integrated into the SEM was used. The outcomes of this analysis revealed that zinc constituted 99% of the metallic elements present on the surface. This indicated that the laser treatment predominantly led to the formation of zinc oxide on the surface of the Cu-Zn alloy. Quasi-one-dimensional nanostructures of zinc oxide were created on the porous copper-zinc alloy metal substrate [154]. This was achieved by using laser processing with a beam power of 330 W and a duration of 23 s.  
Figure 11: Temperature field in the sample during laser treatment with a beam power of 330 W and an exposure duration of 23 s [154]. Figure 13a showcases SEM images illustrating a metal-semiconductor ZnO/Cu nanocomposite and ZnO nanowires that had developed on the brass surface of the sample. The process maintained a maximum temperature below 600 \({}^{\circ}\)C. The resulting nanostructures were mainly vertically oriented ZnO nanowires that formed on the oxide layer. The nanowires had an average cross-sectional dimension of approximately 30-40 nm and a length ranging from 500 to 600 nm. Some nanowires even reached lengths of up to 1 \(\upmu\)m, with a density of 10-20 per square micrometer. When the temperature increased, oxidation processes and diffusion of zinc from the inner layers to the surface increased. This results in the formation of longer nanowires and a more vigorous lateral growth at the root part. However, once the nanowires reach a certain length, their growth slows down due to a decrease in zinc transport efficiency towards the top. Consequently, the length of ZnO nanowires did not exceed 3 \(\upmu\)m under the specified laser treatment conditions [154]. The controlled temperature during the process played a crucial role in determining the type and sizes of the resulting nanostructures. In areas where the temperature exceeded 600 \({}^{\circ}\)C, the nanowires coexisted with nanosheets. These nanosheets had varying lengths of between 0.5 and 3 \(\upmu\)m and diameters ranging from 40-60 nm. The longitudinal dimension of the nanosheets extended up to 3 \(\upmu\)m, while the transverse size was 1 \(\upmu\)m (Figure 13b).