The rapid development of nanotechnology has revolutionized research in applied sciences, including biomedical, cosmetic, infrastructure, electronics, and food packaging ^[1]. The production and use of nanomaterials are growing in various industrial processes [2,3,4]^[2][3][4]. The global market for these materials was valued at 16.3 billion dollars in 2021 ^[5], and it is projected to reach between 45 billion [6,7]^[6][7] and 62.8 billion dollars in 2031–2032 ^[5].

Nanomaterials are generally selected based on their desired applications. They can be synthesized through chemical, physical, or biological methods. Chemical methods involve co-precipitation, chemical reduction of metal salts, electrochemical processes (electrolysis), microemulsion, pyrolysis, photochemical reactions (irradiation), sonochemistry, sol–gel, and solvothermal techniques. Physical methods include arc discharge, electron beam lithography, ion implantation, inert gas condensation, mechanical crushing, grinding, and spray pyrolysis. Biological methods usually rely on biosynthesis approaches using plant extracts, bacteria, fungi, algae, enzymes, and biomolecules ^[8]. The choice of a specific method often dictates the properties of the particles and the resulting characteristics. Nanomaterials can be synthesized using a bottom-up or top-down approach ^[9].

Nanomaterials are generally classified based on their production into carbon-based materials, metals, dendrimers, and compounds ^[10]. Carbon-based nanomaterials typically contain carbon and exist in morphologies such as hollow tubes, ellipsoids, or spheres.

On the other hand, inorganic nanoparticles are produced from carbon-free materials and are classified into two major categories: metals and metal oxide nanoparticles. In most cases, nanoparticles are produced from metals such as platinum (Pt), silver (Ag), gold (Au), cadmium (Cd), cobalt (Co), iron (Fe), copper (Cu), and zinc (Zn) [9,11]^[9][11].

Metal-based nanomaterials are valuable and have a wide range of applications in various industries, including electronics, medical, dental, textiles, coatings, food packaging, and wastewater treatment [1,6]^[1][6]. Other emerging potential uses include dispersions and coatings, consolidated materials, biomedicine, and nanodevices ^[5], and in recent years, the development of nanomaterial applications in consumer products, such as UV filters in sunscreen, odor-resistant textiles, tumor therapies ^[12], lithium-ion batteries for electric vehicles, and solar panels ^[13].

Water treatment applications will likely increase the global demand for nanomaterials ^[6] and the growing demand for electronic products, mainly due to their superparamagnetic properties ^[14]. With the increasing application of nanomaterials, the industry is also growing, with an estimated direct employment of 300,000 to 400,000 in Europe. These materials are dominant primarily in tire manufacturing as a polymer filler, in toothpaste, or as an anticoagulant in powdered foods ^[13]. These applications stem from their physicochemical properties and their small size, which result in a high surface area-to-volume ratio, increased reactivity, and ideal optical properties ^[1], offering a larger surface area compared to the same mass of bulk materials, making them more chemically reactive ^[15].

Reports by Harish et al. show that nanomaterials exhibit various functionalities such as dimensionality (0–3D), morphology (low and high aspect ratio), porosity (macro-, nano-, mesoporous), composition (carbon, inorganic, organic, and hybrid), origin (natural, incidental, designed, bioinspired), phase (monophasic, multiphasic), and dispersion state (dispersed or aggregated) ^[16].

Studies by Chaudhary demonstrate that adding nanomaterials modifies the fundamental properties of materials, such as flexibility, durability, flame resistance, barrier properties, and recycling properties ^[17]. Additionally, material properties can be modified through deposition or doping ^[18]. This fact can lead to performance improvements, such as the deposition of an anti-reflective coating on the front surface of solar cells, reducing reflection losses by 8% ^[19], increasing the conductivity of semiconductors ^[20], improving the barrier properties of bio-based packaging materials ^[17], enhancing the photocatalytic activity of TiO₂ ^[1], and strengthening materials ^[21]. Moreover, as nanoparticles are added to a common material, they refine the grain to some extent, forming an intragranular or intergranular structure, thus improving the grain boundary and promoting the mechanical properties of the materials. For example, adding 3% by weight of nano-SiO₂ to concrete can improve its compressive strength, flexural strength, and tensile strength by splitting. Adding 3% nano-empty fruit bunch fibers to kenaf epoxy composites can significantly enhance their tensile strength, elongation at break, and impact resistance ^[22].

Deposition of sacrificial and structural material on the substrate is the first step in surface micromachining and can be achieved through chemical processes such as chemical vapor deposition (CVD), which is commonly used for nanomaterial manufacturing, electrodeposition, vapor phase epitaxy (VPE), and thermal oxidation, or through physical processes such as physical vapor deposition (PVD) and casting ^[23].

Vapor deposition methods enable a higher-purity surface coating without organometallic compounds. Currently, CVD is the most promising technology for the functionalization of nanoparticles on an industrially relevant scale. This method has multiple variations, including thermally activated, plasma-enhanced, photo-initiated, and oxidative CVD, to name just a few ^[24].

2. Deposition of Nanoparticles on Ceramic Substrates

The deposition of nanoparticles on different substrates has garnered attention due to the changes it generates in material properties. The functionalization of ceramic substrates has enabled new applications in optical and medical fields, among others. These substrates exhibit different mechanical, optical, electrical, catalytic, and magnetic properties depending on the type of nanoparticle used for functionalization. As a result, new nanoparticle deposition techniques on these substrates have been developed, among which [25,26,27,28,29]^{[25][26][27][28][29]} stand out.

2.1. Deposition by Electron Gun Evaporation

Electron beam deposition is used to grow thin films of metals with very high melting points or highly pure metals. The precursor is evaporated with gas and then deposited onto the substrate as a film. This method has gained popularity due to its rapid deposition and ability to generate different metal or non-metal film types ^[30]. In the study conducted by Somayeh Jalilpour et al. ^[25], tantalum oxide nanolayers were prepared on a glass substrate (1 × 20 × 20) mm³ using an ETS160 system at a pressure of 3 × 10⁻⁷ Torr. The layers were obtained under a high vacuum using the electron gun evaporation method (Edwards E19A3). The purity of tantalum oxide was 99.9%, and the deposition rate was 0.2 Å/s. The substrate temperature was kept constant at 300 K. Before the deposition process, the substrates were cleaned with deionized water, acetone, and ethanol for 15 min each using an ultrasonic method. The thickness of the layers (30, 60, 90, and 120 nm) was measured using a quartz crystal technique (Sigma Instrument, SQM–160, Fort Collins, CO, USA) from the deposition angle of the layers, which was vertically oriented. The study on the coatings’ crystalline nature and morphological evolution was characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. Surface morphology and roughness were obtained through analysis using an atomic force microscope (AFM) ^[25].

2.2. Physical Vapor Deposition (PVD)

Physical vapor deposition is a vaporization coating technique that involves the transfer of material at the atomic level under vacuum conditions. This technique can be applied to metals, ceramics, and semiconductors. The process is similar to chemical vapor deposition (CVD), except that physical vapor deposition uses a solid precursor instead of a gas-phase precursor in CVD. The process consists of four stages: the evaporation of the material to be deposited or the precursor using a high-energy source such as an electron beam, the transport of vapor to the substrate, the reaction between the substrate atoms and the reactive gas, and finally, the deposition of the coating onto the substrate surface ^[31] (See Figure 1). In the study conducted by Sanath Kumar Honnali et al. [33]^[32], thermoelements were fabricated using glass as the substrate. The substrate underwent a wet chemical cleaning process followed by steam degreasing. Subsequently, the chamber was loaded with O₂ to perform a 15-min plasma cleaning, varying the pressure from 8 × 10⁻² mbar to 1 × 10⁻¹ mbar. This plasma cleaning increases the Si–O functional groups, thus enhancing the adhesion of thin films on the substrate. Then, ZnO was deposited in the cathodic sputtering with pure zinc as the target at a substrate-reactive distance of 5 cm. The chamber was evacuated to a base pressure of 2 × 10⁻⁵ mbar to minimize residual background impurities. Several deposition cycles were performed at different oxygen partial pressures. The pressure ranged from 9 × 10⁻⁴ mbar to 3 × 10⁻³ mbar, maintaining a total working pressure (O₂ + Ar) of 8 × 10⁻³ mbar for each deposition cycle. A power of 16 W with a deposition rate of 10 nm/min and a deposition time of 10 min resulted in a film thickness of 100 ± 10 nm.

2.3. Plasma-Enhanced Chemical Vapor Deposition (PECVD)

Plasma-enhanced chemical vapor deposition is known as a fast and clean technique for surface modification, where plasma is implemented to achieve more localized and controlled deposition on the substrate. This technique is commonly used on silicon templates to coat them at low temperatures with the desired material and can be applied also to ceramics and polymers. Figure 2 shows a schematic of the plasma-enhanced chemical vapor deposition, where, from the equipment perspective, an inert gas flow is used to prevent secondary reactions, along with a vacuum system and a magnetic field. From the material perspective, the precursor is to be deposited, followed by the target substrate [34]^[33]. In the study conducted by Noresah et al. [35]^[34], they report the functionalization of an ultrafiltration membrane by depositing two monomers onto the membrane surface under vacuum conditions. A cylindrical quartz vacuum chamber measuring 30 cm in length and 6 cm in diameter was used as the reactor. The UF membrane sample (Dimensions: 6 cm × 15 cm) was placed on flat silicon wafers before being transferred to the chamber. A copper coil antenna connected to a 13.56 MHz radiofrequency plasma generator was positioned through the quartz window of the chamber. Firstly, a vacuum condition was created inside the chamber by turning on the vacuum pump to remove the air from the reactor. The monomer 2-hydroxyethyl methacrylate was vaporized in a stainless steel flask before being delivered to the vacuum chamber by controlling the fine metering valve. A back cooling plate was installed as a substrate support to maintain the membrane temperature. The chamber’s desired operating pressure (<100 mtorr) was maintained using a proportional integral derivative-controlled butterfly valve connected to a capacitance manometer. The optimized flow rate and power of acrylic acid plasma (0.75 sccm; 40 W) and the deposition of 2-hydroxyethyl methacrylate (0.4 sccm; 50 W) were used throughout the modification process. Some methods stand out for their low cost, such as electrochemical deposition or spray deposition. Electron beam gun evaporation allows the production of nanolayers, which are widely used for their nonlinear optical properties that change depending on the thickness of the obtained film. This method, in turn, modifies the material’s dielectric properties since increasing the film’s thickness increases the material’s bandgap ^[25]. The electrochemical deposition also imparts materials with nonlinear optical and photoelectronic properties, which depend on the morphology of the obtained nanowires. These properties enable applications in sensors, solar cells, and thin film transistors; this technique is highlighted as a low-cost alternative ^[27].

3. Deposition of Nanomaterials on Polymeric Substrates

The functionalization of polymeric substrates, similar to ceramic substrates, has allowed for new applications of these materials in various areas, including medicine, photonics, and sensors. These substrates exhibit different thermal, mechanical, optical, and catalytic properties depending on the nanomaterial used for functionalization.

3.1. Simultaneous and Consecutive Electrochemical Deposition

Nanoparticle electrochemical deposition can be performed through two different pathways, as shown in Figure 3; they are known as simultaneous electrochemical deposition and consecutive electrochemical deposition [46]^[35]. This technique is applicable also to metal and to ceramic matrices.

3.1.1. Simultaneous

In this method, nanoparticles of two different types are simultaneously deposited, as the name implies. As reported by Zekerya Dursun et al. [46]^[35], electrodes are doped with gold and silver nanoparticles by immersing two electrodes in a solution of chloroauric acid, which serves as the precursor for gold nanoparticles, and potassium hexachloroplatinate, which serves as the precursor for silver nanoparticles. A potential of 0.8 V to −1.1 V is then applied for ten cycles to produce the doping.

3.1.2. Consecutive

In this technique, unlike simultaneous deposition, the process is performed in stages, doping first with one material and then with the other. Taking the case of the study by Zekerya Dursun et al. [46]^[35], for this method, immersion in a solution of potassium hexachloroplatinate is performed with a potential of 0.8 V to −1.1 V, followed by immersion in a solution of chloroauric acid with a potential of 0.1 V to −0.9 V, each for ten cycles.

3.2. Chemical Vapor Deposition (CVD)

Chemical vapor deposition follows the same principle as Enriched Chemical Vapor Deposition, the difference being that PECVD introduces precursors with a plasma gas capable of ionizing the precursors. In contrast, CVD introduces chemical precursors into the reaction chamber that thermally decompose to form solid films without plasma [34]^[33]. The experimental system reported in the study by Hui Kun et al. [39]^[36] for this technique consists of six parts, as shown in Figure 4: a gas device, a high-temperature furnace, a graphite reaction chamber, a carbon layer sample, a vacuum pump, and a tail gas treatment device. The gas system is divided into two parts, one for argon and the other for propylene, each equipped with a flow meter. The graphite reaction chamber comprises a front graphite channel, a front reaction chamber, a rear reaction chamber, and a rear graphite channel. This design ensures that the reaction gas passes through the porous structure of the carbon layer sample completely. In the study by Hui Kun et al. [39]^[36], a temperature of 1600 °C is reported inside the furnace, which is maintained stable for 30 min, and the temperature in the graphite reaction chamber is approximately 50 °C lower than that of the furnace. A high-temperature chemical reaction will cause mass loss in the carbon layer, so comparative experiments are performed to reduce the error. The process is divided into four stages. First, the furnace is evacuated using the vacuum pump, then argon is introduced until the pressure exceeds atmospheric pressure. Once reached, the outlet valve is opened, and the furnace is heated to the reaction temperature with the reaction gas. At this point, the argon valve is closed. At the end of the reaction, the reaction gas valve is closed, and the argon valve is opened again [39]^[36].

3.3. Electrophoretic Deposition

Electrophoretic deposition is a widely used technique that promises cost-effective deposition of nanoparticles with relevant applications, such as obtaining antibacterial properties and improving the biocompatibility of a ceramic compound. It is used to uniformly coat an electrode immersed in a stable suspension. The cathode and anode are subjected to an electric field, inducing the movement of precursor particles to the substrate [47]^[37]. The electrophoretic deposition can be applied to ceramic, metal, and polymer substrates. Figure 5 illustrates the setup used by Huanyu Li et al. [40]^[38] for electrophoretic deposition, where doping of nano-silica onto carbon fibers is performed. A carbon fiber anode is immersed in distilled water containing nano-silica colloids, and a graphite cylinder is used as the counter electrode. In this technique, voltage and time parameters can be varied, typically ranging from 0 V to 3 V throughout 0 to 15 min, depending on the desired doping, followed by drying of the specimens. The application techniques employed showcase the strategic deployment of nanomaterial deposition to achieve tailored functional enhancements. Notably, Chemical Vapor Deposition (CVD) demonstrates the potential to create nanoporous structures in polymer composites, substantially elevating mechanical properties and resistance to erosion [39]^[36]. On the other hand, Electrophoretic Deposition (EPD) stands out for its adeptness in enhancing bond properties between nano-silica and carbon fiber surfaces [40]^[38]. It stands out for its low cost, simplicity of operation, and the possibility of applying different coating materials. It is also used to improve the performance of interfacial bonds between a substrate and a precursor, thus improving the mechanical properties. In situ deposition techniques, including creating antimicrobial properties through nano-Cu₂O on chitosan nanofibrous scaffolds, exemplify the versatility of these methodologies. Additionally, the ingenious application of the sol–gel method to deposit NiO nanoparticles on cotton fibers imparts notable photocatalytic activation properties, opening avenues for environmental conservation [41,42]^[39][40]. Pulsed Laser Deposition (PLD) emerges as a promising contributor to wound healing, with the deposition of silver nanoparticles onto specific scaffolds showcasing enhanced antibacterial activity [43]^[41]. The strategic selection of nanomaterials and matrices further underlines the potency of these techniques, with examples such as nano-silica on carbon fiber offering improved mechanical properties, nano-Cu₂O on chitosan nanofibrous scaffolds displaying potential for wound healing, and NiO nanoparticles on cotton contributing to environmental conservation. A notable method involves depositing photocatalytic micron-thick TiO₂ coatings using a microblast technique on titanium metal and FTO-coated glass substrates. This technique demonstrates scalability and cost-effectiveness, showing potential for practical applications. In enhancing adhesion and inter-particle connectivity of TiO₂ coatings, both furnace and microwave plasma treatments have been explored. Plasma-treated TiO₂ coatings exhibit increased particle packing density, resulting in substantially improved photocurrent density measurements compared to their as-deposited counterparts, thus elevating the application possibilities of this technology. In a separate study, {[PMo₁₂O₄₀]³⁻/PAMAM}_n multilayer films are synthesized through an LBL electrostatic assembly technique. These films, marked by uniformity and homogeneity, provide a matrix for the in situ electro-deposition of Pt micro–nano clusters. The resulting Pt micro–nano clusters with a unique flower-like structure become immobilized on the surface of the {[PMo₁₂O₄₀]³⁻/PAMAM}_n multilayer films. Electro-deposition conditions, such as deposition potential and time, influence the morphology of Pt micro-nano clusters. The resultant Pt-clusters–{PMo12/PAMAM}3 composite films exhibit robust electrocatalytic activities, particularly in methanol oxidation and improved CO tolerance [45]^[42]. Furthermore, the direct electrochemical oxidation of sodium borohydride is investigated through Au–Pt-nanoparticles-decorated poly(p-aminophenol) (PAP) films. These bimetallic surfaces, prepared using simultaneous and successive electro-deposition procedures, serve as catalysts for borohydride electrochemical oxidation. Simultaneous electro-deposition of Au–Pt onto the polymer structure enhances oxidation potential and current density. Extensive characterization, including AFM, SEM, XPS, XRD, and CV, sheds light on these modified surfaces’ structural and morphological properties. The outcomes underscore the potential of these bimetallic catalysts for advancing electrochemical applications, offering insights into their catalytic activities and electron exchange numbers [46]^[35].

4. Deposition of Nanomaterials on Metallic Substrates

The functionalization of metallic substrates has allowed for new applications of these materials in optical, medical, environmental, and other fields. These substrates exhibit different mechanical, optical, electrical, catalytic, and magnetic properties depending on the type of nanoparticle used for functionalization.

4.1. Laser Metal Deposition

This technique is mainly based on a fiber laser with a power of ~6000 W that irradiates the substrate while directing the powder of the desired doping material, including metal, ceramic and polymer substrates. Figure 6 shows the laser metal deposition (LMD) process diagram. This technique provides high precision and a rapid deposition rate [48]^[43]. The study by Qi Zhang et al. [49]^[44] reports doping a Ti–6Al substrate with a mixture of TiB₂/Ti64 powders. The system consisted of a diode laser, a rotating powder feeder, and an industrial robot. The laser power used was 1300 W, with a beam diameter of 3.5 mm and a scanning speed of 10 mm/s. The scanning overlap distance between adjacent paths was 1.92 mm, corresponding to a 40% overlap ratio. The powder feed rate and corresponding layer height were 6.5 g/min and 0.7 mm, respectively. Additionally, the temperature of the Ti64 substrate was 480 °C. All parameters were optimized to prevent cracking of the titanium matrix.

4.2. Electrochemical Deposition

Electrochemical deposition is similar to electrophoretic deposition as it occurs in an electrochemical cell. It is carried out using different configurations with electrodes submerged in an electrolyte mixed with the precursor, which is then subjected to a voltage to induce doping. In the study by C. Augello et al. [50]^[45], the substrate was immersed in a solution of monomers acting as precursors. When the voltage was applied, the monomers underwent chemical polymerization on the substrate. This method offers advantages such as improving the interfacial bond between the coating material and the substrate.

4.3. Atomic Layer Deposition (ALD)

ALD is a particular variant of the CVD technique. In ALD, gas-phase reactants are also introduced into a reaction chamber to form the desired material through surface chemical reactions. The difference is that, in ALD, the precursors are pulsed alternately, one at a time, with an intermediate purge of inert gas [51]^[46]. This technique is based on sequential and self-limiting surface reactions. Most ALD processes involve binary reaction sequences where two surface reactions occur to form the layer. This method offers advantages such as precise control over film thickness and can be applied to metal and ceramic substrates [52]^[47]. In the study by Sheng-Hao et al. [53]^[48], the substrate was deposited in a commercial ALD system with the precursor and H₂O at a chamber temperature of 200 °C. The precursor container was heated to 70 °C, and the H₂O container was kept at room temperature during the ALD processing. A cycle consisted of six steps: precursor 1/dosing time, soak time, evacuation time; precursor 2/dosing time, soak time. During ALD processing, there is a constant flow of carrier gas. Furthermore, chemical vapor deposition of carbon nano-onions on Fe/Fe₃C matrices offers corrosion protection, while atomic layer deposition of nano Sn–O₂ on titanium demonstrates biocompatibility. Laser metal deposition with nano-SiCp on AlSi10Mg alloy influenced the microstructure, decreasing SiCp size and intensifying the reaction between SiC and the aluminum matrix. Other notable findings include electrophoretic deposition of chitosan-reinforced Baghdadite ceramic nanoparticles on stainless steel 316 L to improve biological and physical characteristics, electrophoretic deposition of polyaniline (PANI) nanofibers on copper for corrosion protection, and in situ deposition of Pt nanoparticles on nanopore stainless steel for high active hydrogen evolution reaction. These findings contribute to a comprehensive understanding of nanomaterial deposition techniques and their potential applications, facilitating the development of advanced materials with tailored properties in nanotechnology. The CVD stands out as an economical and effective alternative for the deposition of nanomaterials. It allows for the modification of different materials by providing nanostructures on their surface. For example, nitride semiconductors like gallium nitrides and aluminum nitrides can be produced using CVD, forming nanostructures known as quantum confinement points. These nanostructures allow the materials to be utilized in a wide range of optical and microelectronic devices [87]^[49].