A tunable nano-antenna and a method for manufacturing the same

Abstract

This invention discloses a tunable nanoantenna and its fabrication method, belonging to the field of nanoantenna technology. The tunable nanoantenna comprises, from top to bottom: an ordered metal mesh nanoelectrode layer, Fe... 3 O 4 The invention comprises a magnetic nanosphere layer, a silicon nanopillar micro / nanostructure layer, a substrate layer, and a lower electrode layer. This invention proposes a tunable nanoantenna and its fabrication method. Specifically, this invention combines silicon nanopillars with Fe... 3 O 4 By combining magnetic nanospheres and utilizing their synergistic effect, a composite nanoantenna with magnetic response and optical resonance characteristics can be constructed. This not only breaks through the limitations of single-material control, but also enables more flexible performance control through the dual effects of magnetic and optical fields.

Description

A tunable nanoantenna and its fabrication method Technical Field

[0001] This invention belongs to the field of nanoantenna technology, and particularly relates to a tunable nanoantenna and its fabrication method. Background Technology

[0002] With the rapid development of photonics and nanotechnology, nanoantennas, as core devices for controlling light fields and electromagnetic waves, have demonstrated significant value in fields such as optical imaging, sensing, and information processing. Traditional nanoantennas typically rely on a single material (such as metals or high-refractive-index media) to achieve specific functions, and their controllability is limited by the inherent properties and geometry of the material, making it difficult to meet the needs of complex light field control and multifunctional applications.

[0003] In recent years, multifunctional nanoantennas based on composite materials have gradually become a research hotspot, achieving multidimensional control of optical performance by introducing magnetic materials or special structures. However, existing technologies are mostly limited to independently controlling magnetic or optical fields, making it difficult to simultaneously achieve efficient and precise synergistic control of multiple physical fields. In addition, traditional methods often rely on complex nanofabrication processes when constructing micro- and nanostructures, resulting in high fabrication costs and poor structural stability, which limits their widespread application. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a tunable nanoantenna and its fabrication method. Specifically, this invention combines silicon nanopillars with Fe3O4 magnetic nanospheres, utilizing their synergistic effect to construct a composite nanoantenna with magnetic response and optical resonance characteristics. This not only overcomes the limitations of single-material control but also achieves more flexible performance tuning through the dual effects of magnetic and optical fields.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] One of the technical solutions of this invention:

[0007] A tunable nanoantenna, comprising, from top to bottom:

[0008] The structure consists of an ordered metal mesh nanoelectrode layer, an Fe3O4 magnetic nanosphere layer, a silicon nanopillar micro / nano structure layer, a substrate layer, and a lower electrode layer.

[0009] Beneficial effects: This invention aims to provide a novel tunable nanoantenna, which achieves multi-dimensional dynamic control of frequency, directionality, and resonance intensity by combining a silicon nanopillar high refractive index dielectric resonant light-trapping layer and an Fe3O4 nanosphere resonant frequency dynamic adjustment layer with optical resonance and magnetic response characteristics.

[0010] Optionally, the surface of the Fe3O4 magnetic nanosphere layer is modified with Janus Fe3O4 nanosphere particles containing hydrophobic and hydrophilic groups.

[0011] Furthermore, the hydrophobic group is a long-chain alkyl group or a fluorine atom.

[0012] Optionally, the diameter of the Fe3O4 nanospheres in the Fe3O4 magnetic nanosphere layer is 500-1000 nm.

[0013] Optionally, the diameter of the silicon nanopillars in the silicon nanopillar micro / nano structure layer is 300-800 nm, and it is smaller than the diameter of the Fe3O4 nanospheres.

[0014] The second technical solution of the present invention:

[0015] A method for fabricating a tunable nanoantenna includes the following steps:

[0016] (1) A silicon nanopillar micro / nano structure layer is formed on one side of the substrate layer by photolithography;

[0017] (2) Modify Fe3O4 nanospheres into Janus Fe3O4 nanospheres with hydrophobic and hydrophilic groups on the surface; then centrifuge, wash and dry them in sequence; then disperse the modified Fe3O4 nanospheres in CsCl solution, and then drop them onto the ethanol interface for self-assembly; then control the arrangement and distribution of Fe3O4 nanospheres on the liquid surface by applying a gradient magnetic field and / or adding an external surfactant.

[0018] (3) Apply an electric field to transfer the Fe3O4 nanospheres treated in step (2) from the surface of the solution to the surface of the silicon nanopillar micro-nano structure layer to form a Fe3O4 magnetic nanosphere layer;

[0019] (4) Add silver or copper nanowire solution to the surface of the Fe3O4 magnetic nanosphere layer, and use light radiation to guide self-assembly, or use spin coating technology to form an ordered metal mesh nanoelectrode layer.

[0020] (5) A metal thin film is deposited on the other side of the substrate layer by magnetron sputtering as the lower electrode layer.

[0021] Optionally, the preparation process of the silicon nanopillar micro / nano structure layer in step (1) is as follows:

[0022] The cleaned silicon wafer is treated with HF solution and photoresist is spin-coated. The photoresist-coated silicon wafer is then placed in a photolithography machine, exposed to ultraviolet light using a mask, and then developed to remove the photoresist from the unexposed areas.

[0023] The developed silicon wafer is washed with deionized water and dried with nitrogen; then reactive ion beam etching is performed to obtain a silicon nanopillar micro-nano structure layer.

[0024] Furthermore, the photoresist is AZ 5214 photoresist.

[0025] Furthermore, the spin coating rotation speed is 3000 rpm, and the time is 30 seconds; and / or,

[0026] The conditions for ultraviolet light exposure are: the light source is UV, the wavelength is 365nm, and the exposure time is 345 seconds.

[0027] Furthermore, the conditions for the reactive ion beam etching are as follows:

[0028] The etching gas is either fluorine (CF4) or chlorine (Cl2), the etching gas flow rate is 30:5 sccm, the etching power is 100W, and the etching time is 25 minutes.

[0029] Optionally, the preparation process of the Fe3O4 nanospheres in step (2) is as follows:

[0030] The co-precipitation method was used to dissolve ferric chloride and ferrous sulfate in deionized water, add a dispersant (selected from PVP, SDS or sodium citrate) and stir until homogeneous to obtain a mixed solution; the mixed solution was heated to 50-80℃, and ammonia water was added dropwise while stirring (dropping rate of 0.1-0.5 mL / min) until the pH reached 8-10, and the mixture was stirred at a constant temperature for 30-120 minutes, followed by separation, washing with water and drying to obtain Fe3O4 nanospheres with uniform morphology.

[0031] Furthermore, the ratio of ferric chloride, ferrous sulfate, and deionized water is 2 mol: 1 mol: 40-100 mL;

[0032] The dispersant is 0.1-1 wt% of the mixed solution.

[0033] Optionally, the specific operation of the modification step in step (2) is as follows:

[0034] First, Fe3O4 nanospheres are ultrasonically dispersed in ethanol (concentration controlled at 1-2 mg / mL), and then dropped onto the surface of a hydrophobic polytetrafluoroethylene (PTFE) membrane. After standing or slightly drying, the nanospheres are uniformly adsorbed on the membrane surface, forming a "semi-embedded" structure of particles, thereby achieving spatial shielding of the lower hemisphere surface.

[0035] Subsequently, the membrane carrying Fe3O4 nanospheres was placed in a sealed reaction vessel containing a solution of hydrophobic group modifiers and heated at 100°C for 4-6 hours. After the reaction was completed, the sample was thoroughly washed with ethanol or isopropanol to remove unreacted silane residues, and the particles were then exfoliated from the membrane surface by ultrasonication. After centrifugation and drying, Janus Fe3O4 nanospheres with one half of their surface having hydrophobic long-chain alkyl groups and the other half retaining hydrophilicity were finally obtained.

[0036] Beneficial effects: Modifying the surface of Fe3O4 nanospheres into Janus particles with both hydrophobic groups (such as long-chain alkyl groups or fluorides) and hydrophilic groups (such as hydroxyl groups) allows these nanospheres to tend to form self-assembled structures on liquid surfaces. The high density and ion-shielding effect of the subsequent CsCl solution further prevents nanosphere aggregation through electrostatic repulsion. Furthermore, the stability and uniform distribution at the interface can be enhanced by controlling the proportion of the modified molecules.

[0037] Further, the hydrophobic group modifier is hexadecyltriethoxysilane (C16TES) or dodecyltriethoxysilane (C12TES); in the solution containing the hydrophobic group modifier, the solvent is ethanol or isopropanol, and the concentration of the hydrophobic group modifier is 1-5 vol%; preferably C16TES, C12TES... 16 The ethoxy groups of TES undergo silanization with the hydroxyl groups on the particle surface. Its long-chain alkyl structure endows the particles with hydrophobic properties. Since the lower half of the particles is shielded by the PTFE film, the reaction only occurs on the upper hemisphere surface exposed in the solution.

[0038] Optionally, the drying conditions in step (2) are: vacuum drying at 50-60°C for 12 hours.

[0039] Optionally, the concentration of the CsCl solution is 0.5-0.8M, the temperature is 30-60℃, and the pH is 8;

[0040] The concentration of the modified Fe3O4 nanospheres in the CsCl solution was 0.3 mg / mL.

[0041] Optionally, the gradient magnetic field in step (2) is generated by a Helmholtz coil, and the specific operation steps are as follows:

[0042] The self-assembled solution is placed in a uniform magnetic field while ensuring that the liquid surface is flat and free of bubbles. The strength of the magnetic field generated by the Helmholtz coil is controlled by a power source.

[0043] The magnetic field strength is 10-60 mT, and the magnetic field direction is generally downward, gradually changing from 45° to 45° to the lower right.

[0044] Beneficial effects: This invention utilizes an externally applied uniform magnetic field to control the arrangement and distribution of Fe3O4 microspheres on a liquid surface. The magnetic microspheres spontaneously form chain-like or mesh-like structures under the guidance of the magnetic field. By gradually adjusting the strength and direction of the magnetic field, the microspheres can be encouraged to diffuse and spread evenly on the liquid surface. Using a gradient magnetic field (e.g., generated by a Helmholtz coil) to dynamically adjust local density eliminates accumulation areas and ensures a final uniform distribution.

[0045] Furthermore, a surfactant (ethylene glycol) may be added during the application of the gradient magnetic field.

[0046] Beneficial effects: In high-concentration CsCl solutions, the surface tension is low. To prevent particle sedimentation, a slowly evaporating, low-surface-tension organic solvent (such as ethanol) is used to assist in the formation of a stable liquid film. Furthermore, by gradually reducing the magnetic field or adding trace amounts of surfactant, self-healing and smooth particle distribution can be achieved.

[0047] Optionally, the electric field in step (3) is an alternating electric field, with the direction of the electric field pointing from the solution surface to the surface of the silicon nanopillar micro / nano structure layer.

[0048] Furthermore, the frequency of the alternating electric field is 1kHz-100kHz; the electric field strength is 1-5V / cm.

[0049] Furthermore, the negative electrode of the electric field device is placed below the solution surface, close to the solution surface; the positive electrode is placed near the surface of the silicon nanopillar micro / nano structure.

[0050] Furthermore, the negative electrode and the positive electrode are selected from platinum electrodes or conductive carbon electrodes.

[0051] Beneficial effects: This invention applies an electric field to transfer Fe3O4 nanospheres from the surface of a solution to the surface of a silicon nanopillar micro / nanostructure. This involves the arrangement, direction, and frequency of the electric field. Specifically:

[0052] Electrode arrangement: Two electrodes are placed, one below the liquid surface in the solution and the other near the surface of the silicon nanopillar micro / nano structure. The electrodes can be metals (such as platinum electrodes) or conductive materials (such as carbon electrodes). One electrode serves as the negative electrode, and the other as the positive electrode, using a power source to generate an alternating electric field.

[0053] Electric field direction: The electric field direction points from the solution surface to the surface of the silicon nanopillar micro / nano structure. Fe3O4 nanospheres migrate along the electric field direction through the electric field force.

[0054] Frequency control: The frequency of the alternating electric field needs to be controlled between 1kHz and 100kHz to generate sufficient particle migration force on the surface of the silicon nanopillar micro / nanostructure without causing the particles to oscillate repeatedly or lose stability. Lower frequencies are suitable for particle migration and distribution, while higher frequencies can lead to excessive thermal effects or drag on the particles.

[0055] Therefore, under the action of the electric field force defined in this invention, Fe3O4 microspheres are efficiently and uniformly transferred to the surface of the silicon nanopillar array.

[0056] Optionally, the silver or copper nanowires in the solution have a diameter of 15-20 nm and a length of 2-3 μm.

[0057] Furthermore, the concentration of the silver or copper nanowire solution is 0.03-0.05 mg / mL.

[0058] Optionally, the light source used in the photo-guided self-assembly process described in step (4) is ultraviolet light with a wavelength of 370 nm and a power of 20-110 mW / cm². 2 The irradiation time was 10 minutes and the irradiation angle was 18°.

[0059] Beneficial Effects: The ordered meshing of silver or copper nanowires in this invention is achieved using a photoradiation-guided self-assembly method. This method utilizes the photopressure, thermal effect, and photoinduced surface phenomena generated by photoradiation to guide nanowires to self-assemble into ordered structures on a substrate surface or in a liquid phase by controlling the properties of light. The principle of this method includes: photoradiation pressure, photothermal effect, surface tension change, and photoinduced aggregation. Photoradiation pressure is transferred to the nanowires through the momentum of photons, causing them to move and align. The photothermal effect refers to the absorption of light of a specific wavelength by the nanowires and its conversion into heat energy, with localized heating promoting the movement and aggregation of nanoparticles. Irradiation can also change the surface tension of the liquid phase, guiding nanoparticles to aggregate towards regions with low surface tension, thereby forming ordered structures. Furthermore, illumination can also guide the spontaneous aggregation of nanowires by changing their surface properties (such as charge, hydrophilicity / hydrophobicity). This invention precisely controls the intensity and irradiation area of ​​light by adjusting parameters such as the wavelength, power, and irradiation angle of the light source, prompting nanoparticles to self-assemble along the light intensity gradient or radiation pressure direction. Among them, the advantages of the photo-radiation guided self-assembly method include high-precision control, non-contact assembly, large-area preparation, high efficiency and adjustability.

[0060] Furthermore, after self-assembly, the structure can be stabilized by cooling and / or heat treatment.

[0061] Optionally, the conditions for the magnetron sputtering process in step (5) are:

[0062] The target materials are chromium (Cr), platinum (Pt), and pure gold (Au), with a purity of 99.99%.

[0063] The working atmosphere is argon (Ar), the gas pressure is adjusted to 2 mTorr, and the gas flow rate is set to 25-30 sccm;

[0064] The vacuum level of the sputtering system is less than 1×10 -6 Torr, magnetic field strength set to 45G;

[0065] The target voltage is set to -400V, the power is 120-150W, and a DC power supply is used.

[0066] Optionally, the deposition rate during the deposition process is 0.5 nm / s and the deposition time is 600 seconds to achieve a film thickness of 300 nm.

[0067] The third technical solution of this invention:

[0068] The above-mentioned tunable nanoantennas have applications in photonic data storage, cryptography, color measurement sensing, and 3D holographic imaging.

[0069] Compared with the prior art, the present invention has the following advantages and technical effects:

[0070] This invention provides a tunable nanoantenna based on a stacked structure of silicon nanopillars and iron(III) oxide (Fe3O4) microspheres, and its fabrication method. The tunable nanoantenna is fabricated using a magnetically driven interface self-assembly technique. This antenna utilizes the high refractive index optical resonance characteristics of silicon nanopillars and the magnetic response characteristics of Fe3O4 microspheres, achieving precise adjustment of the resonant frequency and optimization of signal transmission performance through dual modulation of magnetic and optical fields.

[0071] Unlike traditional nanoantennas, this invention integrates magnetic materials and high-refractive-index media at the micro / nano structure level, overcoming the limitations of a single control mechanism. This antenna, under stimulated conditions, can generate surface plasmon waves, which can help alter the material's color. Furthermore, the tunable nanoantenna's reflectivity can be controlled by adjusting different incident angles and polarization states. This material, with its customizable reflectivity, holds broad application prospects in ultra-compact photonic data storage, cryptography, color metrology sensing, 3D holographic imaging, and the fabrication of SPP-based photonic devices. Attached Figure Description

[0072] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0073] Figure 1 is a structural diagram of the tunable nanoantenna prepared in Example 1 of the present invention; wherein, 1-ordered metal mesh nanoelectrode layer; 2-Fe3O4 magnetic nanosphere layer; 3-silicon nanopillar micro / nano structure layer; 4-substrate layer; 5-lower electrode layer;

[0074] Figure 2 is a SEM image of the planar silicon substrate used in Embodiment 1 of the present invention;

[0075] Figure 3 is a SEM image of the uniform arrangement of magnetic Fe3O4 nanospheres on a planar silicon surface achieved by the self-assembly of magnetic Fe3O4 nanospheres using magnetic drive interface self-assembly technology.

[0076] Figure 4 is a micro / nano structure diagram of silicon nanopillars prepared in Example 1 of the present invention;

[0077] Figure 5 is a SEM image (scale bar is 200 nm) of the uniform arrangement of magnetic Fe3O4 nanospheres on the top of silicon nanopillars achieved by the magnetic drive interface self-assembly technology in Example 1 of the present invention.

[0078] Figure 6 is a SEM image of silver nanowires ordered meshing achieved by the photoradiation-guided self-assembly method in Embodiment 1 of the present invention.

[0079] Figure 7 is a SEM image (scale bar is 500 nm) of the uniform arrangement of magnetic Fe3O4 nanospheres on the top of silicon nanopillars achieved by the magnetic drive interface self-assembly technology in Example 1 of the present invention.

[0080] Figure 8 shows the SEM image of the distribution of nanospheres on the top of silicon nanopillars in Comparative Example 2 without the control of magnetic and electric fields.

[0081] Figure 9 shows the hysteresis loops of magnetic Fe3O4 nanospheres in Example 1 and Fe3O4 nanospheres without surface modification in Comparative Example 1.

[0082] Figure 10 shows the reflectance of different structures (silicon nanopillar array + magnetic Fe3O4 nanospheres in Example 1, silicon nanopillar array, planar silicon + magnetic Fe3O4 nanospheres) in the wavelength range of 300-800 nm;

[0083] Figure 11 shows the arrangement of Fe3O4 microspheres on the top of the silicon nanopillars in Comparative Example 1. Detailed Implementation

[0084] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0085] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0086] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0087] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0088] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0089] This invention proposes a tunable nanoantenna based on a stacked structure of silicon nanopillars and magnetic Fe3O4 microspheres, along with its fabrication method. Employing magnetically driven interface self-assembly technology, the micro / nano structure is constructed through a simple and efficient process, exhibiting significant advantages in resonant frequency tuning, surface plasmon wave excitation, and reflectivity control. This invention provides a new approach to addressing current bottlenecks in nanoantennas regarding multi-physics field manipulation, application flexibility, and fabrication cost, and lays the foundation for applications in cutting-edge fields such as photonic data storage, cryptography, color metrology sensing, and 3D holographic imaging.

[0090] This invention discloses a method for fabricating a tunable nanoantenna, comprising the following steps:

[0091] Step 1: Preparation of Fe3O4 microspheres

[0092] Prepare ferric chloride (FeCl3·6H2O), ferrous sulfate (FeSO4·7H2O), ammonia (NH3·H2O), and deionized water. Add a dispersant (such as polyvinylpyrrolidone PVP, concentration 0.1-1 wt%) as needed to reduce particle aggregation. Specific steps are as follows:

[0093] Weigh FeCl3·6H2O and FeSO4·7H2O in a molar ratio of 2:1 and dissolve them in deionized water, ensuring the solution is homogeneous. Add a dispersant according to the particle morphology and stir until homogeneous. Heat the mixed solution to 50-80℃ and stir continuously. While stirring, add 25-28% ammonia solution dropwise at a rate of approximately 1 mL / min, monitoring the pH of the solution until it reaches 8-10. During this process, the solution gradually turns black, indicating that Fe3O4 nanospheres are beginning to form. Continue stirring the reaction at a constant temperature of 50-80℃ for 30-60 minutes to ensure complete nanosphere formation and obtain uniform particle size and morphology.

[0094] After the reaction is complete, the product is separated using an external magnetic field, and the supernatant is discarded. The product is washed 5-6 times with deionized water until the supernatant is neutral, and then washed 2-3 times with anhydrous ethanol to remove surface organic matter and impurities, ensuring the purity of the product.

[0095] The washed product was placed in a vacuum drying oven and dried at 40-60℃ for 12-24 hours to obtain the final Fe3O4 nanosphere powder.

[0096] Step 2: Fabrication of ordered silicon nanopillar arrays

[0097] The cleaned silicon wafer was treated with HF solution to remove the silicon oxide layer on the surface. Simultaneously, AZ5214 photoresist was spin-coated at 3000 rpm for 30 seconds. The photoresist-coated wafer was then placed in a photolithography machine and exposed to ultraviolet light using a mask for 345 seconds at a UV (365nm) wavelength. Development was performed using a developer to remove the photoresist from unexposed areas. The developed wafer was then rinsed with deionized water and dried with nitrogen. The photolithographically patterned substrate was then placed in a reactive ion beam etching machine and etched using either fluorine (CF4) or chlorine (Cl2) gas. This etching process etched an array of nanopillars onto the silicon wafer. The etching gas flow rate was set to CF4:O2 = 20-30:5-10 sccm, the etching power to 100-120W, and the etching time to 25-30 minutes. Finally, the surface photoresist was removed, yielding the silicon nanopillar micro / nano structure.

[0098] Step 3: Achieve uniform self-assembly of magnetic Fe3O4 nanospheres on top of silicon nanopillars using magnetically driven interface self-assembly technology:

[0099] First, Fe3O4 nanospheres were ultrasonically dispersed in ethanol (concentration controlled at 1-2 mg / mL) and then dropped onto the surface of a hydrophobic polytetrafluoroethylene (PTFE) membrane. After standing or slight drying, the nanospheres were uniformly adsorbed onto the membrane surface, forming a "semi-embedded" structure, thus achieving spatial shielding of the lower hemisphere surface. Subsequently, the membrane containing the Fe3O4 nanospheres was placed in a container containing hexadecyltriethoxysilane (C... 16 TES solution (the solvent used is usually ethanol or isopropanol, C 16 In a sealed reaction vessel with a TES concentration of 1-5 vol%, the reaction was carried out at 100°C for 4-6 hours. 16 The ethoxy groups of TES undergo a silanization reaction with the hydroxyl groups on the particle surface. The long-chain alkyl structure endows the particles with hydrophobic properties. Because the lower half of the particle is shielded by the PTFE membrane, the reaction only occurs on the upper hemisphere surface exposed in the solution. After the reaction, the sample is thoroughly washed with ethanol or isopropanol to remove unreacted silane residues. The particles are then ultrasonically peeled from the membrane surface, centrifuged, and dried to obtain Janus Fe3O4 nanospheres (i.e., surface-modified Fe3O4 nanospheres) with one half of their surface possessing hydrophobic long-chain alkyl groups and the other half retaining hydrophilicity.

[0100] A 0.5M CsCl solution was prepared and slowly heated to 30-50℃ to ensure complete dissolution of the CsCl. The surface-modified Fe3O4 nanospheres were redispersed in the 0.5M CsCl solution at a concentration of 0.3 mg / mL. The solution containing the Fe3O4 nanospheres was gently added dropwise to an ethanol interface with high surface tension. By adjusting the solution concentration, temperature, and pH (pH controlled at 8), the self-assembly of the Fe3O4 nanospheres on the solution surface was promoted, forming a uniformly distributed Janus particle structure. The hydrophobicity and hydrophilicity of the Fe3O4 nanosphere surface were further adjusted by controlling the ratio of long-chain alkyl (hydrophobic) to hydroxyl (hydrophilic) groups, thereby optimizing its stability at the liquid interface. Adjusting the concentration and temperature of the CsCl solution utilized the ion-shielding effect to regulate electrostatic interactions and prevent nanosphere aggregation.

[0101] Install the Helmholtz coils: Ensure both sets of Helmholtz coils are coaxial and maintained at a certain distance (depending on the required magnetic field strength) to generate a uniform magnetic field. The coil current and voltage need precise control. Place the dispersed Fe3O4 microsphere solution in the uniform magnetic field, ensuring the liquid surface is flat and free of bubbles. Control the magnetic field strength generated by the Helmholtz coils via the power supply. The magnetic field strength can be set between 10-50 mT depending on the desired mechanical effect. Initially, the magnetic field strength is low to allow the microspheres to slowly align. As the experiment progresses, gradually increase the magnetic field strength until the microspheres form a uniform distribution. In high-concentration CsCl solutions, the surface tension is low. To prevent particle sedimentation, slowly evaporating, low-surface-tension organic solvent ethanol is used to assist in forming a stable liquid film layer. By gradually decreasing the magnetic field or adding a surfactant, self-healing and smooth particle distribution can be achieved.

[0102] Two electrodes are arranged in the solution, one as the negative electrode and the other as the positive electrode. The negative electrode is placed below the solution surface, close to it; the positive electrode is placed near the surface of the silicon nanopillar array. Platinum or conductive carbon electrodes can be used as electrode materials, ensuring that the electrodes do not react with other substances in the solution during the experiment. The distances between the electrodes and the solution and silicon nanopillar array surfaces are appropriate to generate a uniform electric field. An electric field is applied using a power supply system capable of generating an alternating electric field, with the field direction pointing from the solution surface to the silicon nanopillar array surface. The electric field strength can be adjusted according to experimental requirements, typically set to 1-5 V / cm, ensuring effective migration of the Fe3O4 nanospheres without causing excessive thermal effects. Under the influence of the alternating electric field, the Fe3O4 nanospheres will migrate along the direction of the electric field through the electric force. Adjusting the frequency and strength of the electric field is crucial; too high a frequency will cause particle oscillation and instability, while too low a frequency may not effectively drive particle migration. The frequency of the alternating electric field is controlled between 1 kHz and 100 kHz. Generally, lower frequencies are suitable for particle migration and distribution, effectively avoiding particle oscillation and thermal effects, while higher frequencies can cause excessive drag or thermal effects on the particles. An initial frequency of 20kHz can be set to observe the migration of Fe3O4 microspheres on the liquid surface. By adjusting the frequency, the optimal frequency range for particle migration can be found. After setting the frequency, the electric field strength is adjusted, typically set between 3V / cm, and optimized based on parameters such as the particle size of the Fe3O4 microspheres and the viscosity of the solution. An excessively high electric field strength may cause the particles to move too quickly, resulting in inaccurate distribution; an excessively low electric field strength may fail to effectively drive particle migration.

[0103] Under the influence of an alternating electric field, Fe3O4 microspheres migrate from the solution surface to the surface of the silicon nanopillar array. During migration, the particles gradually approach the surface of the silicon nanopillars along the direction of the electric field and eventually stabilize on the surface of the nanopillar array. Due to the magnetic and charge properties of the Fe3O4 microspheres, they self-assemble on the surface of the silicon nanopillars according to the electric field and electrostatic force to form a uniform distribution, ensuring that the particles do not aggregate.

[0104] Step 4: Electrode preparation

[0105] Fabrication of the upper electrode (ordered metal mesh nanoelectrode layer)

[0106] Silver nanowires with a diameter of 20 nm and a length of 3 μm were dissolved in an ethanol solution. Dispersion was performed using an ultrasonic processor for 30 minutes at a power of 50 W to ensure uniform dispersion and prevent agglomeration. The concentration of the silver nanowires was controlled between 0.03 and 0.05 mg / mL. Too high a concentration would lead to excessively strong interactions between particles, making it difficult to achieve ordered arrangement; too low a concentration might prevent the self-assembly process from proceeding effectively.

[0107] 30 mL of silver nanowire solution was dropped onto the surface of a silicon nanopillar topped with an Fe3O4 nanosphere substrate, ensuring the solution covered the entire area to be treated. Irradiation was performed using a 370 nm wavelength ultraviolet light source with a power of 53 mW / cm². 2 The irradiation time was 10 minutes, the irradiation angle was 18°, and the intensity gradient could control the alignment direction of the nanowires. During the irradiation process, the silver nanowires absorbed light of a specific wavelength and converted it into heat energy; localized heating facilitated the movement and self-assembly of the nanowires. After light-induced self-assembly, the substrate was moved into a cooling device for temperature-controlled treatment. The cooling temperature was set to 8°C (room temperature) to avoid rapid temperature changes that could destabilize the nanowire alignment structure.

[0108] To further enhance the alignment stability of the nanowires, heat treatment can be performed. The substrate is heated to 85°C and maintained for 30 minutes. Silver nanowires are then welded to the substrate surface. Using the same method, the substrate is rotated horizontally by 45° to prepare the nanowire thin film, thus completing the preparation of an ordered mesh-like silver nanowire thin film.

[0109] Fabrication of the lower electrode

[0110] First, prepare a pure gold (Au) target with a purity of 99.99%. Place the substrate in the sputtering system, set the working atmosphere to argon (Ar), adjust the gas pressure to 2 mTorr, and set the gas flow rate to 30 sccm. The vacuum level of the sputtering system should be below 1 × 10⁻⁶. -6Torr. The target voltage was set to -400V, the power to 150W, and a DC power supply was used. The deposition rate was set to 0.5nm / s, and the deposition time was controlled at 600 seconds to achieve a film thickness of 300nm. During sputtering, the magnetic field strength was set to 45G to enhance sputtering efficiency and ensure plasma stability. After deposition, the power was turned off, and the film and substrate were allowed to cool naturally to room temperature.

[0111] Unless otherwise specified, "room temperature" in this invention refers to 20-30℃.

[0112] All raw materials used in this invention were purchased from the market.

[0113] The technical solution of the present invention will be further illustrated by the following embodiments.

[0114] Example 1

[0115] As shown in Figure 1, a tunable nanoantenna comprises, from top to bottom: an ordered metal mesh nanoelectrode layer 1, an Fe3O4 magnetic nanosphere layer 2, a silicon nanopillar micro / nano structure layer 3, a substrate layer 4, and a lower electrode layer 5.

[0116] The fabrication method of the above-mentioned tunable nanoantenna includes the following steps:

[0117] Step 1: Preparation of Fe3O4 microspheres

[0118] (1) Prepare ferric chloride (FeCl3·6H2O), ferrous sulfate (FeSO4·7H2O), ammonia (NH3·H2O) and deionized water. Weigh out FeCl3·6H2O (5.406g) and FeSO4·7H2O (2.78g) in a molar ratio of 2mol:1mol, and dissolve them in 100mL of deionized water to ensure that the solution is uniform. Add dispersant polyvinylpyrrolidone (PVP) according to the required particle morphology. Its concentration in the mixed solution is 0.5wt% (i.e., add 0.5g PVP) to reduce particle aggregation. Stir evenly and set aside.

[0119] (2) Heat the mixed solution to 70°C and stir continuously for 45 minutes; while stirring, add ammonia water with a concentration of 25-28% dropwise, with the dropping rate controlled at 1 mL / min, for a total of about 10 mL, while monitoring the pH value of the solution until it reaches 9;

[0120] (3) After the reaction is complete, the product is separated by an external magnetic field with a strength of 3000–5000 Gs (i.e. 0.3–0.5 T). The supernatant is discarded and the product is washed 6 times with deionized water until the supernatant is neutral. Then, the product is washed 3 times with anhydrous ethanol to remove surface organic matter and impurities to ensure product purity.

[0121] (4) The washed product was placed in a vacuum drying oven and dried at 50°C for 18 hours to obtain Fe3O4 nanospheres with uniform morphology and good dispersion.

[0122] Step 2: Fabrication of ordered silicon nanopillar arrays

[0123] The cleaned silicon wafer was treated with HF solution to remove the silicon oxide layer on the surface, and AZ 5214 photoresist was spin-coated at 3000 rpm for 30 seconds. The photoresist-coated silicon wafer was placed in a photolithography machine and exposed to ultraviolet light using a mask for 345 seconds at a UV (365nm) wavelength. Development was performed using NMD-3 developer to remove the photoresist from unexposed areas. The developed silicon wafer was then rinsed with deionized water and dried with nitrogen. The photolithographically patterned substrate was placed in a reactive ion beam etching machine and etched using fluorine gas (CF4). This etching process etched an array of nanopillars onto the silicon wafer. The etching gas flow rate was set to CF4:O2 = 30:5 sccm, the etching power to 100W, and the etching time to 25 minutes. Finally, the surface photoresist was removed, yielding a silicon nanopillar micro / nanostructure with a diameter of approximately 500 nm and a spacing of 500 nm.

[0124] Step 3: Achieve uniform self-assembly of magnetic Fe3O4 nanospheres on top of silicon nanopillars using magnetically driven interface self-assembly technology:

[0125] First, Fe3O4 nanospheres were ultrasonically dispersed in ethanol (concentration controlled at 1.5 mg / mL) and then dropped onto the surface of a hydrophobic polytetrafluoroethylene (PTFE) membrane. After standing or slight drying, the nanospheres were uniformly adsorbed onto the membrane surface, forming a "semi-embedded" structure, thus achieving spatial masking of the lower hemisphere surface. Subsequently, the membrane containing the Fe3O4 nanospheres was placed in an incubator containing hexadecyltriethoxysilane (C... 16 TES solution (using ethanol as solvent, C 16 In a closed reaction vessel with a TES concentration of 3 vol%, the reaction was heated at 100°C for 5 hours. 16 The ethoxy groups of TES undergo a silanization reaction with the hydroxyl groups on the particle surface. The long-chain alkyl structure endows the particles with hydrophobic properties. Because the lower half of the particle is shielded by the PTFE membrane, the reaction only occurs on the upper hemisphere surface exposed to the solution. After the reaction, the sample is thoroughly washed with ethanol or isopropanol to remove unreacted silane residues. The particles are then ultrasonically peeled from the membrane surface and washed three times with anhydrous ethanol or deionized water to remove unreacted modifiers. The resulting surface-modified Fe3O4 nanospheres are then vacuum-dried at 55°C for 12 hours to remove solvent and moisture. Finally, Janus Fe3O4 nanospheres are obtained, with one half of the surface possessing hydrophobic long-chain alkyl groups and the other half retaining hydrophilic properties.

[0126] A 0.5M CsCl solution was prepared and slowly heated to 40℃ to ensure complete dissolution of CsCl. The surface-modified Fe3O4 nanospheres were redispersed in the 0.5M CsCl solution, with the Fe3O4 nanosphere concentration controlled at 0.3 mg / mL. The solution containing Fe3O4 nanospheres was gently added dropwise to the ethanol interface with high surface tension. The concentration, temperature (25℃), and pH value of the solution (8) were controlled to promote the self-assembly of Fe3O4 nanospheres on the solution surface, forming a uniformly distributed Janus particle structure.

[0127] 32) Install the Helmholtz coil: Ensure that the two sets of Helmholtz coils are coaxial and maintain a certain distance (coil voltage is 4V, current is 0.5A, magnetic field strength is 40mT, distance is 5cm) to generate a uniform magnetic field; place the Fe3O4 microsphere solution dispersed in step 31) in the uniform magnetic field, while ensuring that the liquid surface is flat and free of bubbles; control the magnetic field strength generated by the Helmholtz coil through the power supply; subsequently, the magnetic field strength can be gradually reduced or the self-healing and smooth distribution of particles can be achieved;

[0128] 33) Two electrodes are arranged in the solution, one as the negative electrode (platinum material electrode) and the other as the positive electrode (gold material electrode); the negative electrode is placed below the solution surface and close to the solution surface; the positive electrode is placed near the surface of the silicon nanopillar array.

[0129] An electric field is applied using a power supply system capable of generating an alternating electric field, with the field direction pointing from the solution surface to the surface of the silicon nanopillar array, and the field strength being 3 V / cm. Under the influence of the alternating electric field, the Fe3O4 nanospheres will migrate along the direction of the electric field through the electric force; the specific operation is as follows:

[0130] The initial frequency of the alternating electric field was controlled at 20kHz. The migration of Fe3O4 microspheres on the liquid surface was observed, and the most suitable frequency for migration was determined to be 50kHz. After setting the frequency, the electric field strength was adjusted and set to 3V / cm.

[0131] Under the influence of an alternating electric field, Fe3O4 microspheres migrate from the solution surface to the surface of the silicon nanopillar array. During migration, the particles gradually approach the surface of the silicon nanopillars along the direction of the electric field and eventually stabilize on the surface of the nanopillar array. Due to the magnetic and charge properties of the Fe3O4 microspheres, they self-assemble on the surface of the silicon nanopillars according to the electric field and electrostatic force to form a uniform distribution, ensuring that the particles do not aggregate.

[0132] Step 4: Electrode preparation

[0133] 41) Preparation of the upper electrode

[0134] Silver nanowires with a diameter of 20 nm and a length of 3 μm were dissolved in an ethanol solution; dispersion was performed using an ultrasonic processor for 30 minutes at a power of 50 W to ensure uniform dispersion and prevent agglomeration. The concentration of the silver nanowires was controlled at 0.05 mg / mL.

[0135] 30 mL of silver nanowire solution was dropped onto the surface of a silicon nanopillar topped with an Fe3O4 nanosphere substrate, ensuring the solution covered the entire area to be treated; irradiation was performed using a 370 nm wavelength ultraviolet light source with a power of 53 mW / cm². 2 The irradiation time was 10 minutes, and the irradiation angle was 18° to control the alignment of the nanowires. After light-induced self-assembly, the substrate was transferred to a cooling device for temperature-controlled treatment. The cooling temperature was set to 8°C, and the cooling time was 30 minutes.

[0136] To further enhance the alignment stability of the nanowires, heat treatment was performed. The substrate was heated to 85°C and maintained for 30 minutes to weld the silver nanowires onto the substrate surface, thus completing the preparation of an ordered mesh-like silver nanowire film.

[0137] 42) Preparation of the lower electrode

[0138] First, prepare a pure gold (Au) target with a purity of 99.99%. Place the substrate in the sputtering system, set the working atmosphere to argon (Ar), adjust the gas pressure to 2 mTorr, and set the gas flow rate to 30 sccm. The vacuum level of the sputtering system should be below 1 × 10⁻⁶. -6 Torr. The target voltage was set to -400V, the power to 150W, and a DC power supply was used. The deposition rate was set to 0.5nm / s, and the deposition time was controlled at 600 seconds to achieve a film thickness of 300nm. During sputtering, the magnetic field strength was set to 45G to enhance sputtering efficiency and ensure plasma stability. After deposition, the power was turned off, and the film and substrate were allowed to cool naturally to room temperature.

[0139] Example 2

[0140] A method for fabricating a tunable nanoantenna includes the following steps:

[0141] Step 1: Preparation of Fe3O4 microspheres

[0142] The difference from Example 1 is that the ammonia droplet addition rate was controlled at 0.5 mL / min, the heating temperature was 70°C, and the stirring time was extended to 90 minutes to improve particle uniformity. Simultaneously, sodium dodecyl sulfate (SDS, 0.2 wt%) was used as a dispersant instead of PVP to further reduce particle aggregation.

[0143] Step 2: Fabrication of silicon nanopillar arrays

[0144] The difference from Example 1 is that, after cleaning the silicon wafer, an alumina template was used as an etching mask. An 80nm pore size template was prepared by anodizing and then applied to the silicon wafer surface. Reactive ion etching (RIE) was used for etching at a gas flow rate of CF4:O2 = 20:10 sccm, an etching power of 120W, and an etching time of 30 minutes, forming an array of silicon nanopillars with a diameter of approximately 80nm and a spacing of 100nm.

[0145] Step 3: Self-assembly of Fe3O4 nanospheres

[0146] The difference from Example 1 is that hexadecyltriethoxysilane was replaced with dodecyltriethoxysilane (C12TES) as a long-chain alkyl modifier, the reaction time was shortened to 4 hours, the concentration of the long-chain alkyl modifier was increased to 5 vol%, the concentration of CsCl solution was adjusted from 0.5 M to 0.8 M, and the solution temperature was increased to 60 °C, further optimizing the ion shielding effect and particle arrangement stability.

[0147] The magnetic field strength of the Helmholtz coil was set to 50 mT; the electric field strength was adjusted from 3 V / cm to 4 V / cm, and the electric field frequency range was adjusted to 50 kHz; and polyethylene glycol (PEG 400, volume fraction 0.1%) was added to the solution to increase the dispersion stability of Fe3O4 microspheres.

[0148] Step 4: Electrode preparation

[0149] The difference from Example 1 is that,

[0150] Top electrode: Copper nanowires with a diameter of 15 nm and a length of 2 μm were used instead of silver nanowires, with a concentration controlled at 0.03 mg / mL. The solution was coated onto the substrate surface using spin coating technology (3000 rpm, 30 seconds) and then fixed by heat treatment (80 °C, 20 minutes).

[0151] Bottom electrode: Platinum (Pt) target material is used, sputtering power is 120W, gas flow rate is Ar = 25sccm, and film thickness is controlled at 200nm.

[0152] Figure 2 is a SEM image of the planar silicon substrate used in Embodiment 1 of the present invention;

[0153] Figure 3 is a SEM image of the uniform arrangement of magnetic Fe3O4 nanospheres on a planar silicon surface achieved by the self-assembly of magnetic Fe3O4 nanospheres using magnetic drive interface self-assembly technology.

[0154] Figure 4 shows the silicon nanopillar micro / nano structure prepared in Example 1 of the present invention;

[0155] Figure 5 is a SEM image (scale bar is 200 nm) of the uniform arrangement of magnetic Fe3O4 nanospheres on the top of silicon nanopillars achieved by the magnetic drive interface self-assembly technology in Example 1 of the present invention.

[0156] Figure 6 is a SEM image of silver nanowires ordered meshing achieved by the photoradiation-guided self-assembly method in Embodiment 1 of the present invention.

[0157] Figure 7 is a SEM image (scale bar is 500 nm) of the uniform arrangement of magnetic Fe3O4 nanospheres on the top of silicon nanopillars achieved by the magnetic drive interface self-assembly technology in Example 1 of the present invention.

[0158] Comparative Example 1: Fe3O4 microspheres without surface modification

[0159] The difference from Example 1 is that in step 3, the unmodified Fe3O4 microspheres are directly dispersed in an ethanol solution (Fe3O4 microsphere concentration 3 mg / mL), and then self-assembled according to the steps of Example 1. Other steps and conditions are the same as in Example 1.

[0160] Results and Analysis:

[0161] Figure 11 shows the arrangement of Fe3O4 microspheres at the top of the silicon nanopillars in Comparative Example 1. As can be seen from the figure, the Fe3O4 microspheres are not uniformly arranged at the top of the silicon nanopillars, and some microspheres agglomerate.

[0162] Because no hydrophobic / hydrophilic modifications were made, the microspheres exhibited poor stability at the liquid interface, resulting in reduced self-assembly efficiency.

[0163] Comparative Example 2 did not apply magnetic field control

[0164] The difference from Example 1 is that in step 3, the magnetic field control and electric field control of the Helmholtz coil are cancelled, and Fe3O4 microspheres are deposited on the surface of the silicon nanopillar array only by resting and natural volatilization.

[0165] Results and Analysis:

[0166] Figure 8 shows the SEM image of the distribution of nanospheres on the top of silicon nanopillars in Comparative Example 2 without the control of magnetic and electric fields. The image shows that the distribution of the nanospheres is random and lacks a regular arrangement. Furthermore, localized areas experience particle accumulation due to electrostatic effects, significantly reducing the photoelectric performance of the nanoantenna.

[0167] In summary, by comparing the examples and comparative examples, we can see that:

[0168] 1. Surface finishing:

[0169] In the embodiments, surface modification effectively improved the interfacial stability and uniformity of the Fe3O4 microspheres, significantly enhancing the performance of the nanoantenna. In contrast, in Comparative Example 1, the unmodified microspheres exhibited obvious aggregation and uneven arrangement.

[0170] 2. Magnetic field control:

[0171] In this embodiment, the synergistic effect of the magnetic and electric fields resulted in a more uniform distribution of the microspheres on the silicon nanopillars. In contrast, in Comparative Example 2, the lack of magnetic field control led to a highly random arrangement of the microspheres, affecting the photoelectric properties of the antenna.

[0172] Therefore, by optimizing surface modification, etching parameters, and field control techniques, the embodiments of the present invention further improve the performance of nanoantennas, while the comparative examples highlight the importance of these key steps.

[0173] Figure 9 shows the hysteresis loops of the magnetic Fe3O4 nanospheres in Example 1 and the unmodified Fe3O4 nanospheres in Comparative Example 1. The figure shows that for the micro / nano structure with uniformly ordered nanoparticles, the material with high saturation magnetic induction can generate a strong magnetic field, indicating a high magnetic moment density. It also shows low coercivity, making magnetization and demagnetization easy, indicating that the material is readily magnetized and rapidly demagnetized after the external magnetic field is removed. This rapid magnetization and demagnetization performance is suitable for applications requiring frequent magnetization switching. High magnetic flux density transmission enables efficient magnetic performance within a small volume. Therefore, it can be widely used in microwave and radio frequency components such as antennas.

[0174] Compared to uniformly ordered nanoparticle composite structures on micro / nano structures, disordered nanoparticle composite structures on micro / nano structures exhibit lower saturation magnetic induction and lower magnetization. However, they possess relatively high coercivity, are less prone to demagnetization after magnetization, and demonstrate strong "memory" capabilities. This results in a highly stable magnetization state, making them suitable for applications requiring long-term magnetization. While they exhibit strong resistance to external interference—maintaining their original magnetization even under strong external magnetic field interference—they are less suitable for microwave and radio frequency components such as antennas.

[0175] Figure 10 shows the reflectance of different structures (silicon nanopillar array + magnetic Fe3O4 nanospheres in Example 1, silicon nanopillar array, silicon plane + magnetic Fe3O4 nanospheres) in the wavelength range of 300-800 nm; it can be seen from this figure that the silicon nanopillar and Fe3O4 nanosphere stacked structure in Example 1 has a lower reflectance.

[0176] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A tunable nanoantenna, characterized in that, From top to bottom, it includes: an ordered metal mesh nanoelectrode layer, an Fe3O4 magnetic nanosphere layer, a silicon nanopillar micro / nano structure layer, a base layer, and a lower electrode layer.

2. The tunable nanoantenna according to claim 1, characterized in that, The Fe3O4 magnetic nanospheres in the Fe3O4 magnetic nanosphere layer are modified with hydrophobic and hydrophilic groups on their surface.

3. The tunable nanoantenna according to claim 1, characterized in that, The Fe3O4 magnetic nanosphere layer has a diameter of 500-1000 nm; and / or, the silicon nanopillar micro / nano structure layer has a diameter of 300-800 nm.

4. A method for fabricating a tunable nanoantenna, characterized in that, Includes the following steps: Step 1: Form a silicon nanopillar micro / nano structure layer on one side of the substrate using photolithography; Step 2: Modify Fe3O4 nanospheres to form Janus nanostructures with hydrophobic and hydrophilic groups on their surface. Fe3O4 nanospheres were then subjected to centrifugation, washing, and drying. The modified Fe3O4 nanospheres were dispersed in a CsCl solution and then dropped onto an ethanol interface for self-assembly. The arrangement and distribution of the Fe3O4 nanospheres on the liquid surface were controlled by applying a gradient magnetic field and / or adding an external surfactant. Step 3: An electric field was applied to transfer the Fe3O4 nanospheres treated in step 2 from the surface of the solution to the surface of the silicon nanopillar micro / nano structure layer, forming a Fe3O4 magnetic nanosphere layer. Step 4: A silver or copper nanowire solution was dropped onto the surface of the Fe3O4 magnetic nanosphere layer, and self-assembly was guided by light radiation or by spin coating technology to form an ordered metal mesh nanoelectrode layer. Step 5: A metal thin film was deposited on the other side of the substrate layer by magnetron sputtering as the lower electrode layer, finally obtaining the tunable nanoantenna according to any one of claims 1-3.

5. The method for fabricating a tunable nanoantenna according to claim 4, characterized in that, The specific modification operation in step 2 is as follows: the Fe3O4 nanospheres are ultrasonically dispersed in ethanol and dropped onto the surface of a polytetrafluoroethylene membrane. After standing or drying, the Fe3O4 nanospheres are uniformly adsorbed on the membrane surface. Then, the membrane carrying the Fe3O4 nanospheres is placed in a solution containing a hydrophobic group modifier and heated at 100°C for 4-6 hours. After the reaction is completed, the membrane is washed, ultrasonically exfoliated, centrifuged, and dried in sequence to obtain the Janus Fe3O4 nanospheres.

6. The method for fabricating a tunable nanoantenna according to claim 4, characterized in that, In step 2, the concentration of the CsCl solution is 0.5-0.8 M, the temperature is 30-60℃, and the pH is 8; the concentration of the modified Fe3O4 nanospheres in the CsCl solution is 0.3 mg / mL.

7. The method for fabricating a tunable nanoantenna according to claim 4, characterized in that, The gradient magnetic field mentioned in step 2 is generated by a Helmholtz coil. The specific operation steps are as follows: the self-assembled solution is placed in a uniform magnetic field, and the magnetic field strength generated by the Helmholtz coil is controlled by a power supply; the magnetic field strength is 10-60 mT.

8. The method for fabricating a tunable nanoantenna according to claim 4, characterized in that, The electric field in step 3 is an alternating electric field, with the direction of the electric field pointing from the solution surface to the surface of the silicon nanopillar micro / nanostructure layer; and / or, the frequency of the alternating electric field is 1 kHz-100 kHz; the electric field strength is 1-5 V / cm; and / or, the negative electrode in the electric field is placed below the solution surface, close to the solution surface; the positive electrode is placed near the surface of the silicon nanopillar micro / nanostructure layer; and / or, the negative electrode and the positive electrode are selected from platinum electrodes or conductive carbon electrodes.

9. The method for fabricating a tunable nanoantenna according to claim 4, characterized in that, The light source used in step 4, which involves photoradiation-guided self-assembly, is ultraviolet light with a wavelength of 370 nm and a power of 20-110 mW / cm². 2 The irradiation time was 10 minutes and the irradiation angle was 18°.

10. The method for fabricating a tunable nanoantenna according to claim 4, characterized in that, The conditions for magnetron sputtering described in step 5 are as follows: the working atmosphere is argon, the gas pressure is adjusted to 2 mTorr, and the gas flow rate is 25-30 sccm; the vacuum degree of the sputtering system is less than 1×10⁻⁶ m / s. -6 Torr, magnetic field strength of 45 G; target voltage of -400V, power of 120-150 W, using DC power supply; and / or, the deposition conditions are: deposition rate of 0.5 nm / s, deposition time of 600 seconds.

Images