Creation of One- and Two-Dimensional Copper and Zinc Oxides Semiconductor Structures

Abstract

The most effective methods for the synthesis of nanostructured copper and zinc oxides, which have unique properties and potential applications in a variety of fields including electronics, photonics, sensorics, and energy conversion, are analyzed. Special attention is paid to laser-based methods for synthesizing oxide nanostructures, with an emphasis on the importance of controlling power density distribution to influence the quality and properties of the nanomaterials. The great significance of wavefront shaping techniques for controlling laser-initiated processes is highlighted, which enable precise control over the phase and amplitude of light waves to achieve desired outcomes in optics and laser-assisted formation of one- and two-dimensional structures of oxide semiconductor materials. Diffractive computer optics is presented as a powerful tool for precise beam control. The significance of laser-induced thermochemical processes for creating and improving the properties of ZnO and CuO-based nanomaterials is discussed. The presented analysis shows that the synthesis of nanocomposites based on ZnO and CuO using pulse-periodic laser treatment, coupled with precise laser beam control using free-form diffractive optics, presents novel opportunities for applications in optoelectronics, sensor technology, electronics and portable energy sources manufacturing, and various other fields.

1. Introduction

Advancements in such branches as sensorics, opto- and microelectronics, and microsystems engineering have resulted in a growing demand for smaller, lighter, and more efficient devices. Great potential in producing advanced components with better performance and lower power consumption has been shown by nanostructured metal oxides [1,2,3]. The use of metal oxide nanomaterials can lead to the development of efficient sensors [4,5,6] and heterogeneous catalysts with fast performance, stability, and high selectivity [7]. Furthermore, oxide materials are also used in solar energy applications [8,9], among others, in the form of heterostructures [10].

It should be noted that one-dimensional (1D)/quasi-one-dimensional and two-dimensional (2D) structures of oxide semiconductor materials possess improved surface activity and high surface area, due to which they demonstrate unique catalytic and sensing properties [11,12]. Their structural anisotropy and dimensional effects lead to the modulation of electronic structure and optical properties, which opens prospects for the use of these materials in electronic and optical devices with a high degree of efficiency. One-dimensional material structures are materials in which their properties change in only one direction, resembling a “linear chain” structure. Materials such as nanofibers, nanowires, or nanotubes find wide application in areas requiring high sensitivity, such as in sensor devices. 1D structures also have high electronic mobility along their axis, which makes them promising for high-speed transistor applications. They can also be used as efficient materials for solar cells, photodetectors, and other optoelectronic devices.

In two-dimensional material structures, atoms or molecules are arranged in a single plane, forming a two-dimensional layer with a nanometer-scale thickness. These materials typically exhibit remarkable electronic, optical, and chemical properties and find wide-ranging applications in various fields, including electronics, photonics, and catalysis. 2D structures such as thin films and layers also have unique structural flexibility and can be easily integrated into various devices [13]. They can be used in microelectronics, memristors, and active elements of flexible electronic systems. Due to these properties, one-dimensional/quasi-one-dimensional and two-dimensional oxide semiconductors offer extensive opportunities for innovative technological solutions in electronics, optoelectronics, energetics, and sensorics. Research in this area continues to expand our understanding of these unique materials and their applications [14].

One-dimensional and two-dimensional copper (CuO) and zinc (ZnO) oxides are different forms of these materials that have some similarities, but also many different properties, and potential applications. The excellent properties of divalent copper oxide and zinc oxide account for their demand in various fields of science and technology. Both compounds, known for their semiconducting properties, which make them attractive for use in electronics and photonics, belong to the class of transition metal oxides. However, despite this, CuO and ZnO have unique properties and are used in different applications [15,16]. CuO copper oxide can be obtained in various forms, including 1D and 2D structures. In 1D form, such as nanowires, CuO has high specific surface activity and is effectively used as a catalyst in various chemical reactions. In this case, quasi-one-dimensional materials usually have a larger surface area compared to 2D structures, which can affect their chemical activity and interaction with the environment [17]. In addition, the semiconducting properties of copper oxide allow its use in solar cells, showing high efficiency in converting solar energy into electrical energy [18]. Zinc oxide is also widely used in electronics, sensorics, and other technologies [19]. It can be used in the form of nanowires, nanofilms, or nanoparticles. ZnO is highly transparent in the visible range of the spectrum, making it an ideal material for solar panels and LED applications [20]. Moreover, the planar structures of zinc oxide limited to two dimensions possess higher transparency than 1D materials. Due to its light-emitting properties, ZnO is also used in optoelectronics and photonics, including the creation of LED displays and lasers [21]. It is interesting to note that both oxides under consideration also have piezoelectric properties, meaning that they can generate electrical charge when mechanically deformed [22]. Thus, both 1D and 2D structures of copper and zinc oxides have special properties that determine their potential use in various applications and make them valuable materials for a variety of innovative applications [23,24,25].

To develop innovative advanced technologies that meet the growing needs of high-tech sectors, promising laser-thermochemical processes for oxidizing metal surfaces are being actively researched [26]. These developments are important for creating more efficient and sustainable devices; for example, the laser-induced thermochemical recording of micro- and nano-dimensional structures is gaining attention for its applications in photonics, particularly in the production of optical transducers [27,28,29]. When a laser beam interacts with a material, the primary processes are related to localized heating, in which the energy of the electromagnetic wave is transferred to the substance. One of the key aspects of the laser–matter interaction is the ability to precisely control the laser beam’s parameters, such as the intensity, duration, and wavelength. By manipulating these factors, the interaction can be controlled, achieving desired outcomes [30].

The interaction between laser radiation and metals in the presence of oxygen is a highly significant issue. Ref. [31] highlighted the substantial alteration in the ability of metallic materials to absorb laser radiation based on the thickness of the oxide film and emphasized the importance of considering thermochemical processes occurring on metal surfaces in an oxygen-rich environment. These processes have a profound impact on the heating dynamics, as the formation of the oxide film leads to a significant change in the absorption capacity. Consequently, the temperature–time relationships exhibit noticeable non-linear characteristics. Understanding the behavior of laser radiation when it interacts with metals in an oxidizing environment is crucial for various applications, in which the presence of an oxide film on the metal surface can significantly affect the absorption of laser energy, altering the heating process [32].

Laser thermochemistry investigates chemical processes influenced by the thermal effect of the laser beam, occurring under conditions close to thermodynamic equilibrium. The peculiarities of thermal processes in chemically active media when exposed to a laser beam are studied [33]. The laser beam’s high spatial coherence allows precise focusing, enabling chemical reactions to occur with excellent spatial resolution in specific areas [34]. The nonisothermal nature of the process of metal oxidation opens up opportunities for the effective control of the chemical processes, and laser irradiation serves as a valuable tool in achieving this objective.

To effectively control the laser–matter interaction, it is essential to create a specific intensity spatial profile in the target region of the material. This can be achieved by employing beam parameter transformation systems that have the ability to create the necessary temperature exposure [35]. The effect of laser irradiation of non-transparent materials depends mainly on the ability of the optical system to distribute energy over their surface with a given intensity. The significant interest shown by researchers in this field is evident from the diverse range of optical systems currently in use and being developed [36].

In the case in which an optical component is used to form a specified wavefront, the field distribution in the target region can be determined. This is known as the optical forward problem [37]. However, in order to create an optical component that focuses the beam into a certain region of space, it is necessary to solve the optical inverse problem. This not only involves focusing the beam into the target region on the focal plane but also the formation of a predetermined intensity distribution in this region [38,39]. From a mathematical perspective, creating an optical component that precisely generates the required wave field can be challenging since the solution may not exist or may be unstable. Nevertheless, solutions to these problems can be found [40,41]. One example of an optical inverse problem is the task of directing a beam of light using an optical device into a specific region, such as a line or a figure. In this task, the intensity distribution in the focused region is controlled, but the phase function can be chosen arbitrarily. This degree of freedom allows one to calculate the optical component that provides a predetermined focus [42].

To achieve the desired intensity profile, it is important to create a focusing area with dimensions similar to the smallest possible achievable spot width. This spot dimension is determined by the diffraction process, which thus plays a crucial role in obtaining the desired intensity profile. Sometimes, to solve specific problems, it is required to focus the beam into a region whose longitudinal dimensions are significantly greater than the transverse dimensions that coincide with the diffraction-limited spot width. For such cases, the tasks of focusing the beam into a segment or curve as well as a set of lines are solved [43].

New methods using pulse-periodic laser irradiation to create various types of nanomaterials, such as nanoporous and layered structures from metal-oxide nanowires, have been developed [44,45,46]. By subjecting metallic materials to such laser treatment, a significant increase in the diffusion coefficient was obtained, which is explained as the result of the combined effect of heating and laser-induced vibrations. These vibrations occur mainly in the sound frequency range and are caused by pulse-periodic laser irradiation lasting in the microsecond and millisecond ranges. This combination of heat and vibrations has allowed for the creation of a unique approach for producing quasi-one-dimensional nanostructured metal oxides by the laser–matter interaction. For the further development of methods of laser irradiation to increase the diffusion coefficient and improve mass transfer in solid-phase metallic materials, it is important to analyze the possibilities of creating structures with improved physical and mechanical properties [47]. One of the main challenges in this field is ensuring predeterminate laser exposure across all local areas within the irradiated zone. This challenge can be addressed by modifying the shape of the laser beam and redistributing the energy and power density using appropriate optical systems. This opens up exciting possibilities for utilizing laser irradiation as an advanced technique to manipulate and enhance the properties of various materials.

The main objective of this article is to conduct an analysis of the provided ordered information pertaining to advancements in the application of nano- and microtechnologies using laser irradiation for the creation of one- and two-dimensional materials. In the course of the analysis, special attention is paid to the estimation of the prospectivity and efficiency of the use of these methods for solving various classes of issues and problems. In particular, the synthesis of nanostructured divalent copper oxide and zinc oxide, which have exceptional properties superior to their macroscale analogs, is considered. Furthermore, the use of optical systems to control the intensity and spatial distribution of light waves is subject to review. The results are of great interest for both future scientific investigations and a wide range of practical applications. The advancements in this research field are anticipated to significantly impact various industrial applications.

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].

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].

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. 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 requirements of 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. Liquid-phase routes, including sol-gel-assisted dip-and-spin coating, spray pyrolysis, and electrodeposition, are also used [93]. To create thin films and two-dimensional CuO layers, besides chemical bath deposition (CBD) [94,95,96], atomic layer deposition (ALD) [97,98] is used.

One of the methods for synthesizing one-dimensional and two-dimensional structures of zinc oxide (ZnO) and copper oxide (CuO) is thermal oxidation [99]. This method is based on the controlled oxidative transformation of corresponding metallic precursors at high temperatures in an oxygen or air atmosphere. The thermal oxidation process can be utilized to create nanostructures with different shapes and sizes, making it an important tool in the field of nanotechnology and nanomaterials [100,101]. Thermal treatment is a relatively simple and cost-effective technique that does not require expensive equipment. This method can be easily scaled up for the synthesis of large quantities of material, making it attractive for industrial applications [102]. One of the drawbacks of this method is the complexity of process control. Achieving the desired material properties and structure requires careful control of synthesis parameters such as the temperature, processing time, and gas environment. Additionally, thermal treatment typically involves high temperatures, which may limit its applicability for thermally sensitive materials or certain types of substrates [103].

Laser-based methods are also used for the synthesis of one-dimensional, quasi-one-dimensional, and two-dimensional structures of both zinc oxide (ZnO) and copper oxide (CuO) materials. 1D ZnO structures are fabricated by pulsed laser ablation (PLA), which involves using a high-energy laser to ablate a ZnO target, resulting in the formation of ZnO nanowires or nanorods [104,105]. The method of pulsed laser ablation can be applied to synthesize two-dimensional porous ZnO nanosheets and their hybrids with one-dimensional carbon nanotubes [106]. The SEM image of this kind of hybrid material is presented in Figure 5.

Laser-assisted chemical bath deposition (LA-CBD) is also an efficient method for growing 1D ZnO nanostructures due to its high productivity. In [107], it was shown that, at least for the used parameter range of the continuous-wave (CW) laser, with increasing power of the laser beam during bath deposition, the growth of ZnO nanostructures was enhanced, resulting in improved morphology and electrical conductivity. Laser-ablation synthesis in solution (LASiS), which combines laser ablation with solution chemistry, was used to produce one-dimensional CuO nanowires or nanorods, as well as CuO thin films [108]. Post-ablative laser irradiation of nanomaterials in suspension states was used for additional modification of their geometry: Size and shape [109]. The laser-induced hydrothermal growth (LIHG) [110], which can be realized using continuous laser sources, also seems to be promising.

Laser-assisted chemical vapor deposition (CVD) combines laser irradiation with chemical vapor deposition to grow ZnO and CuO thin films. In [111], it was shown that the average grain size was increased with increasing laser irradiation power density, which, however, at large levels may have resulted in the formation of discontinuous precipitates with large voids. When pulsed laser deposition (PLD) is used to fabricate two-dimensional copper oxide structures, a high-energy laser is used to ablate a copper target, creating a plume of copper atoms. These atoms then condense on a substrate and form thin CuO films, which by their nature can be two-dimensional [112]. Pulsed laser deposition (PLD) can be used to synthesize vertically oriented zinc oxide nanowires [113], as well as to deposit thin films and 2D layers of ZnO on substrates, allowing for precise control over film thickness and properties [114,115]. In [116], it was shown that the quality of PLD thin films deposited by the PLD method is influenced by the substrate temperature. Figure 6 illustrates that at temperatures up to 100 °C, the substrates appear to be covered with clusters of nanoparticles forming a dense film.

Beginning from a certain temperature, the porous structure will initially consist of small grains, which will favor the growth of small particles, limiting the preferential growth in certain directions and affecting the crystallinity of ZnO thin films [116]. It should be noted that laser-based methods offer advantages in terms of control over size, shape, and crystal structure, making them valuable for the fabrication of various nanostructures for research and applications Nevertheless, several challenges and difficulties take place in the synthesis of one-dimensional and two-dimensional ZnO and CuO structures using laser-based or laser-assisted methods. One of these challenges is the need to optimize laser irradiation parameters, such as power, frequency, and pulse duration, to achieve the desired structural characteristics. Additionally, thermal effects and thermal stresses induced by laser irradiation can also negatively impact the quality of the synthesized structures, making monitoring and control of these aspects a critical part of the process.

The distribution of power density within the laser spot can indeed influence the quality of the synthesized structures when using laser-based methods. This is an important factor that affects the growth, morphology, and properties of nanomaterials. Thus, in [117], a method of pulsed laser synthesis in which CO₂ laser irradiation is used for ablating the zinc acetylacetonate in water and alcohol solvents was described. The mechanism of the formation of ZnO nanorods and nanowires involves the aggregation of small particles with the formation of larger solid particles in the form of one-dimensional structures in the process of self-assembly. The length and width of the formed one-dimensional structures depend not only on the irradiation time but also on its intensity. It has been shown that ZnO nanoparticles are formed not only in the peripheral regions of the laser spot characterized by lower power density but also near the irradiation site. However, these nanoparticles do not aggregate into larger ones [117].

Laser-induced chemical deposition was realized in [118], where the ZnO nanowires grew on the deposited nanoparticles, and the area of zinc oxide deposition on the silicon wafer was limited directly by the laser beam. It has been noted that intense laser irradiation can stimulate the nucleation of ZnO, but it may also result in an excessive presence of hydroxide ions and the delocalization of the deposition. In [119], a laser-induced hydrothermal growth (LIHG) process was carried out using a continuous wave diode laser with a profile beam shaper for uniform irradiation over the entire surface area. The settings of laser power distribution, beam velocity, and exposure time allowed for the precise control of the morphology of the produced quasi-one-dimensional ZnO nanostructures. Uniform power density distribution can contribute to the formation of structures with smoother and more homogeneous surfaces, which is crucial for certain applications. A non-uniform distribution, however, may lead to heterogeneity in sizes and shapes within the synthesized nanomaterials. At that, the value of laser power density can influence the crystal structure of the resulting nanomaterials, i.e., may promote the growth of crystals with specific orientations or phases, and at high power densities, the structures may be damaged [120]. This may be important, for example, in creating nanostructures with specific electronic or optical properties [121]. Therefore, the power density distribution can also be used as a means of controlling the synthesis process and obtaining specific types of structures. When synthesizing ZnO and CuO nanostructures using laser irradiation, it is important to consider and optimize the power density distribution within the laser spot to achieve the desired properties and quality of the structures.

3. Wavefront Shaping for Laser-Initiated Processes

To successfully control laser-initiated processes, it is crucial to use appropriate systems that can transform beam parameters. These systems play an important role in achieving the desired outcome by providing the necessary effect. The effectiveness of the exposure to laser beams greatly depends on the precise distribution of energy by the optical system to a specific local area of the object surface with the appropriate intensity. The wide range of optical systems currently in use and under development demonstrates the considerable interest in this area of research [122].

Wavefront shaping is a technique used in optics to manipulate the phase and amplitude of light waves. By controlling these properties, it is possible to shape the wavefront and achieve desired outcomes such as focusing light into specific areas or generating complex intensity patterns [123,124]. This area of research finds application in various methods of laser-assisted formation of one-dimensional (1D)/quasi-one-dimensional and two-dimensional (2D) structures of oxide semiconductor materials [125,126,127]. To determine the distribution of a specific optical element across all relevant areas, one can solve the direct problem of wavefront shaping. However, when it comes to focusing a beam into a particular area, an inverse problem arises. This means that not only must the beam be concentrated in a predetermined area on the optical element’s focal plane but also a predetermined intensity distribution must be achieved in that area [128]. Mathematically, generating an optical element that produces the desired wave field is considered incorrect as a solution may not always exist or could be unstable. Nonetheless, solutions can still be found for such problems.

In [129], a freeform optics design method for illumination and laser beam shaping has been presented, the aim of which is to optimize one or more free-form surfaces to transform the original irradiance distribution into the desired one. The optimization process solves the tailoring optics problem, which is an inverse problem. One of the advantages of this method is that the geometric conditions, the number of free-form surfaces, and the illumination conditions can be easily changed in the process of its solution. As shown in Figure 7, using the known values of the input f(x₁, y₁) and output g(x₂, y₂) irradiance distributions, the ray mapping function from plane $\mathcal{X}$ to plane $\mathcal{Y}$ was estimated. Once the values of (x₂, y₂) were obtained and related to (x₁, y₁), free-form surface optimization was carried out [129].

As an example of an inverse optical problem, one can consider the situation when it is required to focus a beam into a specific region, for example, into a specific figure or line in the focal plane [130,131]. To fulfil such a problem, it is possible to create an optical component that has the desired surface shape since only the intensity distribution is defined in the focal region. In this case, the phase remains arbitrary, which makes it possible to create an optical component capable of manipulating light in the desired way. Two groups of typical beam shaping tasks presented in [132] are shown in Figure 8. The first group includes tasks of redistributing only the intensity distribution of the incident light beam to create a given illuminance in the target plane or a given intensity distribution in the distant zone [133,134,135,136]. When solving tasks of the second group, the both intensity distribution and phase distribution of the incident light beam are redistributed to obtain a predefined illuminance distribution with a predetermined output phase distribution [137,138,139,140].

In [137], the task of forming a predefined illuminance distribution and wavefront is formulated as follows. It is assumed that the following parameters are specified: The illuminance distribution I(x), x ∈ G, formed in the plane z = 0 by an incident beam with a plane wavefront, the desired illuminance distribution L(y), y ∈ D, formed in the output plane z = f, and the desired eikonal Ψ(y) distribution in the same plane (Figure 9). It is necessary to find such functions as u₁(x) and l(y) at which the light beam that passes through the optical element will form in the output plane z = f a predefined illuminance distribution L(y) and a predefined eikonal Ψ(y). Simultaneous control of the illuminance distribution and wavefront requires the use of an optical element with two “working” surfaces—refractive or reflective [137].

Diffractive computer optics is used for focusing laser radiation. It is a powerful tool for controlling the energy distribution and shaping laser beams with high precision, making it an important element in modern laser technology [141]. Its ability to be customized and adapted to different tasks makes it irreplaceable in a multitude of scientific and industrial applications. Diffractive computer optics uses special optical components, such as diffractive gradient lenses and phase masks, to change the phase and amplitude of the laser beam [142,143]. Figure 10 shows a spectral diffraction lens fabricated by direct laser recording [144]. These optical components, which reflect or transmit light, are characterized by the amplitude and phase function of the reflection or transmission, which is determined by the conditions of the wavefield transformation problem to be solved. The components have microscopic surface structures created using nanophotolithography technologies or direct laser writing techniques [145,146]. With the ability to fine-tune the phase and amplitude of the laser beam, diffractive computer optics allows for a high degree of focusing and minimizes the size of the focused spot. This is useful for precise laser material processing and high-resolution imaging.

Thus, wavefront shaping methods are crucial for effectively controlling laser processes. These methods have the potential for various applications, including precise material processing and high-resolution imaging. Wavefront shaping finds applications in the formation of one-dimensional and two-dimensional structures of oxide semiconductor materials and offers significant prospects for further research and development. An effective tool for controlling energy distribution and shaping of laser beams with high precision is diffractive computer optics, rendering it an integral component of innovative laser technologies and scientific investigations.

4. Laser Thermochemical Oxidation for the Formation of ZnO and CuO-Based Nanostructures

In the area of the laser–matter interaction, a significant phenomenon is the capacity to prompt modifications in materials through the influence of intense light waves. Laser irradiation presents a range of opportunities for initiating chemical reactions through diverse mechanisms. These include increasing the temperature of atoms and molecules by thermal exposure, the excitation of energy levels of atoms and molecules by resonance, and rupturing or stimulating molecular bonds through resonant electromagnetic stimulation. It is widely acknowledged that laser beams can induce chemical reactions by generating heat within chemically active substances. Studies have demonstrated that laser irradiation yields distinct thermochemical and vibrational impacts, resulting in divergent outcomes compared to the so-called traditional heating [147].

In the context of metallic materials, the oxidation process holds particular significance. When metallic materials undergo oxidation within a chemical reaction induced by laser irradiation, the thermal and chemical facets of the system become intricately linked. This connection is influenced by the reaction rate, which is reliant on temperature, as well as variations in the material’s energy absorption capabilities during the growth of the oxide film. In this case, the absorbed energy serves as the feedback transfer coefficient. If the target product of the reaction absorbs more laser energy, the reaction is accelerated due to heat absorption, establishing positive feedback in the system. This implies that as the concentration of the target product rises, the absorption of laser irradiation increases. Consequently, the reaction experiences a self-acceleration phenomenon known as thermochemical instability [148]. This occurrence is frequently observed during the formation of oxide films on metallic materials when exposed to laser beams.

Conversely, if the reaction product absorbs less energy than the initial substance, negative feedback ensues within the system. As a result, the chemical process decelerates and stabilizes itself. By controlling the quantity of the absorbed energy, it becomes feasible to manipulate and regulate the thermochemical processes unfolding within the system. The use of laser irradiation allows for precise regulation of the quantity of thermal energy introduced into the system while considering discrepancies in absorption across different regions of the material’s surface. The primary aim is to avert thermochemical instability that represents the situation where positive feedback triggers an accelerated oxidation reaction after a specific time frame. Through the control of laser duration and power distribution, it becomes possible to manipulate the temperature and energy distribution within the material, thereby exerting influence over the oxidation reaction [149].

In [150,151], it has been found that using a laser beam with frequency modulation in the sound and infrasound frequency ranges can result in a substantial enhancement of the diffusion coefficient within materials. This increase is achieved through the combined exposure to laser pulses that introduce heat and induce vibrations. The prerequisite for an additional and very significant increase in the diffusion coefficient in solid materials, especially in metallic materials, during heating either in a non-oxidizing medium or in a medium ensuring selective oxidation is the creation of a dynamic stress–strain state by means of laser-induced vibrations. While the general behavior of this combined effect has been determined, comprehending this recently discovered physical phenomenon represents a noteworthy advancement in the development of innovative processes based on the laser–material interaction [152].

The process of producing composite metal/oxide nanomaterials with the use of pulse-periodic laser treatment was presented in [46]. 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 CO₂ 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 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 °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 μm, 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 µm 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 °C, the nanowires coexisted with nanosheets. These nanosheets had varying lengths of between 0.5 and 3 μm and diameters ranging from 40–60 nm. The longitudinal dimension of the nanosheets extended up to 3 μm, while the transverse size was 1 μm (Figure 13b). In the central part of the samples, where at the end of the heating stage the temperature reached 780 °C, after exfoliation from both the front and back sides of the samples of the initially formed layers containing mainly zinc oxide, an array of two-dimensional nano-objects, as shown in Figure 13c, formed from the zinc-depleted near-surface layer. These objects had a nanometer size (thickness of 70–100 nm) only in one dimension, while in the other two dimensions, this size was macroscopic [154].

In [155], the potential for creating a ZnO/CuO nanocomposite material by laser irradiation of a copper-zinc substrate that had previously undergone surface etching was demonstrated. This process resulted in the formation of monoclinic CuO and wurtzite ZnO on a porous Cu-Zn alloy substrate. It is worth noting that the structure of the surface layers differed between the non-etched and dezincified materials after undergoing oxidation by laser exposure. The specific oxide type formed during laser treatment was determined by the initial surface composition. When laser irradiation was applied to the non-etched material, it led to the creation of ZnO nanowires on the metallic surface. Conversely, laser irradiation of the unzincified surface resulted in the development of a network composed of ZnO nanowires and a thin CuO film on the metallic surface. This study [155] provided valuable insights into the synthesis of ZnO/CuO nanocomposites through the combined use of surface etching and laser treatment techniques.

When pulsed-periodic laser treatment is applied, the material surface undergoes a transformation leading to the formation of anisotropic quasi-one-dimensional and two-dimensional semiconductor structures based on zinc (ZnO) and copper (CuO) oxides. In this case, the microporous brass substrate can function as a conductive interface for the created nanostructures. Morphological attributes hold primary importance across various applications, resulting in the need to control these parameters by modifying the synthesis conditions. The mechanism of laser irradiation’s influence on the growth, morphology, and properties of oxide nanomaterials has been examined, along with the degree of impact of various laser parameters on nanomaterial formation. It has been determined that a controlled temperature during synthesis plays a crucial role in determining the type and size of the resulting nanostructures, and this control can be achieved by adjusting the irradiation time and laser power density. The outlined approach opens up new possibilities for creating oxide nanostructures that have applications in various fields such as optoelectronics, sensorics, the manufacturing of electronic devices and portable energy sources, and many others. The use of free-form diffractive optics [153] within the optical system for precisely focusing the laser beam into a predefined area of the material’s surface enables the effective control of heating and oxidation processes [26,34].

Innovative structures are programmable metasurfaces, surfaces with microscopic elements that allow fine-tuning of the laser radiation characteristics [156]. They act as optical controllers, changing the phase, amplitude, and direction of light waves. Programmable metasurfaces enable the creation of complex optical elements that can form light beams with specified characteristics, providing opportunities for more flexible and precise control of laser beams. This includes the creation of optical lenses, phase gratings, and other optical elements [157]. In diffractive computer optics, they are used to create complex optical systems in order to control light waves with a high resolution. They can be programmed to create specific diffractive elements that can focus light with a high resolution [158]. Diffractive computer optics uses mathematical algorithms and computational methods to optimize and control these optical systems [159]. The combination of programmable metasurfaces and diffractive computer optics enables the creation of adaptive and highly efficient optical systems that can be customized for a variety of applications and conditions, including laser material processing and other areas where precise and flexible control of light is required.

5. Conclusions

One-dimensional/quasi-one-dimensional and two-dimensional structures of oxide semiconductor materials exhibit enhanced surface activity and high surface area, leading to unique catalytic and sensing properties, as well as modulating electronic and optical properties, making them promising for a wide range of electronic, optoelectronic, and energy applications. The most effective methods for the synthesis of nanostructured copper (CuO) and zinc (ZnO) oxides, which have unique properties that make them highly attractive for applications in various fields, were investigated.

Various methods, including hydrothermal synthesis, chemical bath deposition, atomic layer deposition, thermal oxidation, and laser-based techniques, are employed to create one- and two-dimensional structures of zinc oxide (ZnO) and copper oxide (CuO). These methods offer precise control over size, shape, and other properties, making them valuable for nanotechnology research and applications. However, they also require careful consideration of factors such as temperature and growth conditions to achieve the desired structural and electronic characteristics in the synthesized materials. Laser-based methods for synthesizing ZnO and CuO nanostructures involve techniques such as pulsed laser ablation, laser-assisted chemical bath deposition, laser-induced hydrothermal growth, and more. In their implementation, the distribution of power density within the laser spot typically plays a crucial role in influencing the quality, morphology, and properties of the synthesized nanomaterials, highlighting the need for precise control of this parameter to achieve the desired material characteristics.

The use of wavefront shaping techniques is important for controlling laser-initiated processes because it provides the opportunity to precisely control the phase and amplitude of light waves to achieve desired results in optics and the laser-assisted formation of one- and two-dimensional structures of oxide semiconductor materials. The key concept here is the significance of precise spatial control of laser intensity through the utilization of beam parameter transformation systems to regulate laser–matter interactions. Researchers are actively advancing optical systems to efficiently distribute energy over the surfaces of non-transparent materials, addressing optical forward and inverse problems to attain predefined intensity distributions and precise focusing within specific areas. These efforts consider diffraction processes and offer versatile solutions for a wide range of applications. Diffractive computer optics is presented as a powerful tool for precise beam control and has found applications in laser materials processing and high-resolution imaging, emphasizing the versatility and precision of these techniques in optics and photonics.

Laser thermochemical oxidation is used for the formation of ZnO and CuO-based nanostructures. Laser irradiation, when applied to metallic materials, leads to chemical reactions by generating heat within the substances, which can result in the formation of oxide films on the material’s surface. This oxidation process can be controlled by manipulating the absorbed energy, thereby preventing thermochemical instability and allowing for the precise regulation of temperature and energy distribution within the material, influencing the oxidation reaction. The study of laser-thermochemical processes for oxidizing metal surfaces is essential for developing advanced technologies in high-tech sectors, particularly in photonics, by precisely controlling laser beam parameters to achieve desired outcomes. With a particular emphasis on understanding the thermochemical processes occurring on metal surfaces in oxygen-rich environments, these processes can profoundly impact heating dynamics and absorption capacity, making laser irradiation a valuable tool for controlling chemical processes influenced by the thermal effect of the laser beam.

New methods have been developed to create various nanomaterials by using pulse-periodic laser irradiation. These methods use a combination of heating and laser-induced vibrations to significantly increase the diffusion coefficient in metallic materials. This approach allows the creation of unique quasi-one- and two-dimensional nanostructured metal oxides and opens up opportunities to improve the physical and mechanical properties of materials. Achieving predetermined laser exposure throughout the irradiated zone is one of the main challenges, and it can be addressed by modifying the laser beam’s shape and redistributing energy and power density using appropriate optical systems. This extends the promising prospects of using laser irradiation as an advanced method to manipulate and improve the properties of various materials.

The synthesis of nanocomposites based on ZnO and CuO using pulsed-periodic laser treatment is considered. By using free-form diffractive optics within the optical system, the laser beam can be precisely focused on a predefined area of the material’s surface, enabling effective control of heating and oxidation processes. This approach opens up new possibilities for creating oxide nanostructures with applications in such fields as optoelectronics, sensorics, electronic devices and portable energy sources manufacturing, and more.

The innovative structures are programmable metasurfaces, which are surfaces with microscopic elements that allow precise control of laser beam parameters such as the phase, amplitude, and direction of light waves. This enables adaptive and efficient optical systems for laser material processing and other areas where precise control of light is needed. Diffractive computer optics employs mathematical algorithms and computational methods for the optimization and precise control of these optical systems. In combination with advancing lasers and control tools, these prospects maintain a confident expectation of the successful development of the presented methods and technologies.