High-purity structural color coating based on Fano resonance and preparation method

Abstract

The invention discloses a high-purity structural color coating based on Fano resonance and a preparation method. Comprising a reflection metal layer M1, a lossless dielectric layer D1, a coupling metal layer M2 and a lossy dielectric layer D2 which are stacked in sequence, M1D1M2 form a discrete state structure to serve as a narrow-band light absorber, and M2D2 form a continuous state structure to serve as a broadband light absorber; a lossy dielectric layer D2 is formed by nano-particles, and the continuous-state wide-spectrum absorption and phase characteristics are flexibly designed by regulating and controlling the materials, the sizes and the arrangement of the particles; interference coupling is achieved through the shared coupling metal layer M2, Fano resonance is excited in the visible light wave band, and therefore the reflective structural color with high purity, wide color gamut and excellent angle stability is obtained. According to the invention, the broadband continuous state constructed by the nanoparticles is coupled with the Fabry-Perot resonant cavity composed of M1D1M2, the material selection range of the continuous state is expanded, the flexibility of the structural design is improved, a structural color solution with advantages in the aspects of color expression and designability is provided, and the application prospect is wide. And the method has huge application potential in the fields of display, anti-counterfeiting and decoration.

Description

Technical Field

[0001] This invention mainly relates to the field of functional optical thin films and micro / nano structure design, and in particular to a high-purity structural color coating based on Fano resonance and its preparation method. Background Technology

[0002] Color is one of the core elements of human perception and information transmission. Traditionally, color has been achieved primarily through chemical pigments or dyes, which rely on the selective absorption of specific wavelengths of light by their molecular structure. However, chemical colorants have many inherent drawbacks, such as easy fading under ultraviolet radiation, chemical instability at high temperatures, environmental unfriendliness of some pigments containing heavy metals, and color gamut limitations imposed by the physicochemical properties of the material itself.

[0003] Structural color, as an emerging coloring mechanism, offers an important approach to overcoming the aforementioned shortcomings. Structural color originates from the interaction between light and micro / nano-scale physical structures, such as interference, diffraction, and scattering. Compared to chemical color, structural color possesses significant advantages, including theoretical non-fading properties, high brightness, high saturation, and environmental friendliness, demonstrating enormous application potential in high-end displays, anti-counterfeiting encryption, decorative coatings, and sensing.

[0004] Currently, the main technical routes for realizing artificial structural colors include photonic crystals, all-dielectric metasurfaces, plasmon resonance structures, and multilayer interference structures. However, each technical path faces corresponding challenges. Photonic crystal structural colors, such as the nanosphere self-assembly scheme in CN115094645B, can theoretically produce high-purity, high-saturation structural colors, but because their color rendering mechanism relies on the periodic arrangement of microspheres, the color changes significantly with the viewing angle. Plasmon metasurfaces are limited by the intrinsic ohmic loss of metallic materials, often leading to reduced color purity. All-dielectric metasurfaces can reduce losses, but they usually face problems such as complex material structure design. For example, patent CN116360016B achieved wide color gamut, high-purity structural colors by constructing a silicon nitride / silicon-rich silicon nitride / silicon dioxide stacked dielectric metasurface structure on a quartz substrate, but its fabrication process is complex, requiring precision micro-nano processing technologies such as electron beam exposure and etching, resulting in high costs and difficulty in large-scale production.

[0005] In contrast, multilayer film structures based on thin-film interference control color by stacking thin films with different refractive indices, offering advantages such as greater design freedom and the ability to adjust color through film thickness and refractive index systems. For example, patent CN117930411A achieved high-purity red structural colors through a five-layer metal-dielectric thin film structure, but the color performance is mainly concentrated in the red spectrum, resulting in a limited range of colors. Patent CN110749945A improved the reflectivity and purity of structural colors through a multilayer film system with alternating stacks of high and low refractive index materials, but its color realization still relies on a complex multilayer film structure. Overall, traditional multilayer film structures, in pursuing excellent optical performance such as wide color gamut, high purity, and low angular sensitivity, often rely on complex and precise film system designs. This not only places extremely high demands on the uniformity of film thickness, interface quality, and fabrication precision, but also makes it difficult to effectively integrate with low-cost, large-area, and high-yield industrial production. Summary of the Invention

[0006] To address the problems existing in the above-mentioned background technology, this invention proposes a high-purity structural color coating based on Fano resonance and its preparation method, which can play an important role in the fields of functional optical thin films and micro / nano structure design.

[0007] The technical solution of the present invention is as follows: I. A high-purity structural color coating based on Fano resonance: The coating comprises a four-layer structure stacked sequentially from the inside to the outside on the surface of the object: M1D1M2D2, where M1 represents a reflective metal layer, D1 represents a lossless dielectric layer, M2 represents a coupling metal layer, and D2 represents a lossy dielectric layer. The lossy dielectric layer D2 is composed of nanoparticles, wherein the three layers of M1D1M2 constitute a discrete structure, and the two layers of M2D2 constitute a continuous structure. The discrete structure and the continuous structure are coupled through the shared coupling metal layer M2, thereby generating a reflective structural color based on Fano resonance.

[0008] Preferably, the high-purity structural color coating based on Fano resonance consists of only four thin films, including a reflective metal layer M1, a lossless dielectric layer D1, a coupling metal layer M2, and a lossy dielectric layer D2. The M1D1M2 structure acts as a discrete state, serving as a narrowband light absorber; the M2D2 structure acts as a continuous state, serving as a broadband light absorber; coupling occurs through the shared coupling metal layer M2, thereby generating a reflective structural color based on Fano resonance.

[0009] The lossy dielectric layer D2 is composed of nanoparticles. The local surface plasmon resonance effect excited by the nanoparticles in this layer can provide broadband and controllable light absorption and phase modulation in the visible light band, which meets the requirements of the continuous state for broadband background and controllable coupling efficiency.

[0010] The structural design of this invention further broadens the selection of material systems that can be used to construct continuous states. In addition to noble metals, various materials with plasma responsiveness, such as TiN, Ti, and Ni, can be used, thus providing a more flexible material selection basis for performance optimization and low-cost preparation of structural color coatings. Meanwhile, thanks to the random distribution characteristics of the nanoparticles, the optical response of this layer exhibits low sensitivity to the incident angle and polarization state, further enhancing its stability and applicability in practical applications.

[0011] The materials of the total reflection metal layer M1 and the coupling metal layer M2 are both high-reflectivity materials such as Ag, Au, Al and Cu.

[0012] The material of the non-destructive dielectric layer D1 is one of the transparent materials such as TiO2, SiO2, Al2O3, Ta2O5, Nb2O5, HfO2, MgF2, ZnS, Si3N4, LiF and LaTiO3.

[0013] The material of the lossy dielectric layer D2 is one or a mixture of high-loss nanoparticles such as TiN, W, Mo, V, Fe, Ti, Ni, Si, Cr, Ge, Au, Ag, Al and Cu.

[0014] The thickness of the reflective metal layer M1 is 30 nm or more; the thickness of the non-damaging dielectric layer D1 is 1 nm-400 nm; the thickness of the coupling metal layer M2 is 1 nm-60 nm; the thickness of the damaging dielectric layer D2 is 10 nm-100 nm; and the average diameter of the nanoparticles is 10-50 nm.

[0015] The high-purity structural color coating provided by this invention is optically designed based on the Fano resonance principle. By precisely controlling the optical parameters of the non-destructive dielectric layer D1, the structural color can be continuously tunable. Further synergistic adjustment of the geometric parameters of each functional layer enables full color gamut coverage in the visible light band (380 nm-780 nm). The response spectrum of this coating can be finely adjusted by independently controlling parameters such as the thickness of the non-destructive dielectric layer D1, the thickness of the coupling metal layer M2, the thickness of the damaged dielectric layer D2, and the nanoparticle size, demonstrating high design flexibility and programmability. The obtained structural color has advantages such as high color purity and good angular stability, making it suitable for display, anti-counterfeiting, and decorative applications.

[0016] II. A method for preparing a high-purity structural color coating based on Fano resonance: The method is specifically as follows: Step 1: Select a substrate for thin film deposition, and obtain a pretreated substrate after cleaning and processing; Step 2: Prepare the reflective metal layer M1 on the pretreated substrate surface; Step 3: On the surface of the reflective metal layer M1, prepare the non-destructive dielectric layer D1; Step 4: On the surface of the non-destructive dielectric layer D1, prepare the coupling metal layer M2; Step 5: Deposit the damaged dielectric layer D2 on the surface of the coupled metal layer M2 using a solution method.

[0017] The post-cleaning treatment in step 1 specifically involves ultrasonic cleaning with acetone, isopropanol, anhydrous ethanol, and deionized water in sequence to remove surface oil and impurities, followed by drying.

[0018] The substrate is made of polished glass, polished stainless steel, polished mirror aluminum, polyethylene terephthalate, polyimide, polydimethylsiloxane, polyethylene naphthalate, and polymethyl methacrylate, etc.

[0019] The total reflection metal layer M1, the non-destructive dielectric layer D1, and the coupling metal layer M2 in steps 2-4 are prepared by one of the following methods: spin coating, spray coating, scraping coating, brush coating, physical vapor deposition, and chemical vapor deposition.

[0020] The method for preparing the damaged dielectric layer D2 in step 5 is a solution method, including one of the following solutions: spin coating, spray coating, blade coating, brush coating, and flow coating. Specifically, the solution method involves applying a dispersion containing the nanoparticles onto the surface of the coupled metal layer M2.

[0021] The nanoparticles in the dispersion are high-loss nanoparticles such as TiN, W, Mo, V, Fe, Ti, Ni, Si, Cr, Ge, Au, Ag, Al and Cu, with a concentration of 0.01-10 wt%.

[0022] The high-purity structural color coating is used in any of the following, including but not limited to, display devices, decorative coatings, and anti-counterfeiting labels.

[0023] In this invention, a lossy dielectric layer D2 is composed of nanoparticles. By controlling the material, size, and arrangement of the particles, the broadband absorption and phase characteristics of the continuous state can be flexibly designed. The two are coupled through a shared coupling metal layer M2 to achieve interference coupling, thereby exciting Fano resonance in the visible light band and obtaining a reflective structural color with high purity, wide color gamut, and excellent angular stability.

[0024] This invention couples a broadband continuous state constructed from nanoparticles with a Fabry-Perot resonant cavity composed of M1D1M2, expanding the range of materials that can be selected for the continuous state and improving the flexibility of structural design. It provides a structural color solution that has advantages in both color performance and designability, and has great application potential in the fields of display, anti-counterfeiting and decoration.

[0025] Compared with the prior art, the beneficial effects of the present invention are: (1) Enhanced color purity: This invention employs a four-layer film structure based on Fano resonance, M1D1M2D2. The discrete state (M1D1M2) and the continuous state (M2D2) are efficiently coupled through a shared coupling metal layer M2, exciting a reflection spectrum with sharp edges and asymmetric line shape in the visible light band. The resonance spectral line has a narrow half-maximum width and low background reflectance, thereby improving color purity and color gamut.

[0026] (2) Wider range of material choices: The lossy dielectric layer D2 is constructed using nanoparticles to form a continuous state, and its local surface plasmon resonance provides broadband tunable light absorption and phase modulation. This design expands the material selection from noble metals (such as Ge and GST) to a variety of plasmonic-responsive material systems such as TiN, Ti, and Ni, reducing material costs while maintaining optical performance. In addition, this layer can be prepared by solution-based processes such as spin coating and spraying, without the need for complex vacuum equipment. The process is simple, easy to form uniform films over large areas, and compatible with industrial technologies, providing a feasible path for the large-scale, low-cost manufacturing of structural color coatings.

[0027] (3) Simplified structure and programmable design: This invention adopts a simple four-layer film structure, and its color output can be precisely and synergistically controlled through multiple independent parameters, specifically including: the thickness of the lossless dielectric layer D1, the thickness of the coupling metal layer M2, the thickness of the lossy dielectric layer D2, and the particle size of the nanoparticles therein. By systematically designing and matching the above parameters, continuous and precise color control can be achieved throughout the entire visible light band, possessing highly programmable design flexibility. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the high-purity structural color coating based on Fano resonance of the present invention.

[0029] Figure 2 This is the equivalent refractive index diagram when the lossy dielectric layer D2 in this invention uses TiN nanoparticles.

[0030] Figure 3 The simulated reflectance spectrum of the structural color coating provided in Embodiments 1-4 of the present invention.

[0031] Figure 4 For the corresponding Figure 3The color coordinate distribution of the medium reflectance spectrum on the CIE 1931 chromaticity diagram.

[0032] Figure 5 This shows the relationship between the thickness of the SiO2 non-destructive dielectric layer and the mass fraction of the PHPS precursor solution in Examples 5-14 of the present invention.

[0033] Figure 6 These are photographs of the structural color coatings prepared in Examples 5-14 of this invention.

[0034] Figure 7 The test reflectance spectra are those of the structural color coatings prepared in Examples 5-14 of this invention.

[0035] Figure 8 For the corresponding Figure 7 The color coordinate distribution of the medium reflectance spectrum on the CIE 1931 chromaticity diagram.

[0036] Figure 9 The test reflectance spectra are those of the structural color coatings prepared in Comparative Examples 1-5 of this invention.

[0037] Figure 10 For the corresponding Figure 9 The color coordinate distribution of the medium reflectance spectrum on the CIE 1931 chromaticity diagram. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] The accompanying drawings illustrate some embodiments, intended to explain and depict the implementation examples involved in this invention, but are not limited to such embodiments. The technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0040] like Figure 1 As shown, the high-purity structural color coating based on Fano resonance includes a reflective metal layer M1, a lossless dielectric layer D1, a coupling metal layer M2, and a lossy dielectric layer D2. M1D1M2 constitutes a discrete-state structure, serving as a narrowband light absorber. M2D2 constitutes a continuous-state structure, serving as a broadband light absorber. The discrete and continuous states are coupled through the shared coupling metal layer M2, thereby generating a reflective structural color based on Fano resonance.

[0041] The reflective metal layer M1 serves as the total internal reflection layer in the optical interference structure, enabling high reflectivity in the visible light band. Preferably, the reflective metal layer M1 is composed of a metallic material with high reflectivity in the visible light band, such as one of Ag, Au, and Al. Furthermore, the reflective metal layer M1 can be flexible or non-flexible, and its thickness is typically greater than 30 nm to ensure the formation of a continuous, dense, high-reflectivity film.

[0042] The aforementioned lossless dielectric layer D1 provides precise optical phase modulation. By adjusting the thickness of this layer, the optical path difference can be actively controlled, thereby introducing the desired rapid phase shift near the target resonant wavelength and achieving fine-tuning of the discrete-state resonant position.

[0043] The coupling metal layer M2 serves as a key functional layer connecting the discrete state (M1D1M2) and the continuous state (M2D2). This layer, together with the underlying reflective metal layer M1, forms the upper and lower reflection interfaces of the Fabry-Perot (FP) resonator, and also forms a broadband continuous state with the upper lossy dielectric layer D2. The coupling mechanism arises from the leakage of the field components of the continuous-state resonator to the discrete-state resonator through the coupling metal layer M2. To achieve clear Fano resonance, this coupling needs to be weak. When its thickness is too large, the two resonators will decouple, causing the Fano resonance effect to disappear, and only the spectral characteristics of the continuous state will be observed. By optimizing its thickness, the coupling strength and ratio between the discrete and continuous states can be effectively controlled, thereby directly affecting the line shape of the Fano resonance spectrum.

[0044] The lossy dielectric layer D2 and the coupling metal layer M2 together form a broadband, weakly absorbed optical background, and interfere with the underlying discrete structure (M1D1M2) through the shared coupling metal layer M2. By finely controlling the optical parameters of this layer, the spectral shape, absorption intensity, and phase relative to the discrete state can be actively modulated, thereby controlling the Fano resonance spectral lines.

[0045] To achieve broadband low-reflectance characteristics of the continuous state in the visible light band, a nanoparticle structure with random arrangement and non-uniform particle size distribution can be used. In this structure, nanoparticles of different sizes excite specific resonant wavelengths, and their combined responses can merge to form a broadband low-reflectance band. The optical properties of the continuous state can be synergistically modulated by material, particle size, and thickness. Material selection affects the light propagation speed and intrinsic loss, thereby adjusting the light intensity and phase. Particle size distribution and arrangement regulate the resonant coverage and coupling strength, thereby adjusting the absorption bandwidth and spectral line shape, while thickness variation directly modulates the optical path length and phase accumulation. The synergistic effect of these multiple parameters jointly achieves broadband low-reflectance characteristics in the visible light range.

[0046] The lossy dielectric layer D2 is composed of randomly distributed nanoparticles and exhibits broadband absorption in the visible light range. The nanoparticles include one or a mixture of TiN, Ti, Ni, Si, Cr, Ge, Au, Ag, Al, and Cu nanoparticles.

[0047] By precisely controlling the geometric parameters of the thickness of each functional layer, continuous and precise control of structural color can be achieved. Key geometric parameters include the thickness of the non-destructive dielectric layer D1, the thickness of the coupling metal layer M2, the thickness of the destructive dielectric layer D2, and the particle size of the nanoparticles within this layer. Optimizing these parameters allows for full color gamut coverage within the visible light range (380-780 nm), and enables comprehensive control of color brightness, saturation, and bandwidth.

[0048] The discrete state M1D1M2 includes a substrate. The substrate can be composed of any conventional substrate material, such as polished glass, polished stainless steel, polished mirror aluminum, polyethylene terephthalate, polyimide, polydimethylsiloxane, polyethylene naphthalate, and polymethyl methacrylate, etc.

[0049] The preparation methods of the reflective metal layer M1, the non-destructive dielectric layer D1 and the coupling metal layer M2 are not limited to any method, such as currently known physical vapor deposition technology (PVD, such as thermal evaporation, electron gun, ion implantation, sputtering, etc.), chemical vapor deposition technology (CVD) or solution method (such as spin coating, spraying, scraping, brushing, etc.).

[0050] The damaged dielectric layer D2 is prepared by a solution-based process, which involves coating a dispersion containing nanoparticles onto the upper surface of the coupling metal layer M2. The methods involved include, but are not limited to, spin coating, spray coating, blade coating, and brush coating. The coating thickness can be controlled by adjusting the concentration of nanoparticles in the dispersion, coating process parameters (such as coating speed), or by performing multiple coatings.

[0051] The solvent system used in the dispersion should be selected based on the chemical stability of the nanoparticles. For chemically stable nanoparticles (such as Au, Ag, Al, TiN), common organic solvents such as alcohols, ethers, alkanes, or aromatics, or mixtures thereof with water, can be used. For easily oxidized nanoparticles (such as Ti, Ni, Cr, Si, Ge), inert nonpolar solvents (such as high-boiling-point alkanes) or strictly dehydrated and deoxygenated ether solvents are preferred, and surface ligands are usually required to maintain dispersion stability. In some embodiments, the first solvent includes water, ethanol, isopropanol, propylene glycol alkyl ether esters (such as propylene glycol methyl ether acetate), and mixtures thereof, with a boiling point between 60-200 °C.

[0052] Specific embodiments of the present invention are as follows: Examples 1-4: Top Layer Materials In this embodiment, the overall structural features of the high-purity structural color coating based on Fano resonance are as described above. Figure 1 As shown, the coating comprises, from bottom to top, a reflective metal layer M1, a non-damping dielectric layer D1, a coupling metal layer M2, and a damaging dielectric layer D2. The damaging dielectric layer D2 is composed of nanoparticles.

[0053] In this embodiment, Ag is used for the reflective metal layer M1 and the coupling metal layer M2, SiO2 is used for the non-destructive dielectric layer D1, and TiN, Ti, Ni, and Cr nanoparticles are used for the destructive dielectric layer D2. This embodiment specifically selects TiN, Ti, Ni, and Cr nanoparticles as the materials for the destructive dielectric layer D2 to demonstrate the scalability of the invention in material selection. Specifically, the thickness d1 of the reflective metal layer M1 is 100 nm, the thickness d3 of the coupling metal layer M2 is 12 nm, the thickness d2 of the non-destructive dielectric layer D1 is 150 nm, the thickness d4 of the destructive dielectric layer D2 is 60 nm, and the diameter distribution of the nanoparticles used ranges from 20 to 40 nm.

[0054] The only difference between Examples 1-4 is that the damaged dielectric layer D2 is made of TiN, Ti, Ni, or Cr nanoparticles, respectively; the rest are the same.

[0055] Nanoparticles of different materials, when forming a lossy dielectric layer, can achieve broadband tunable light absorption through localized surface plasmon resonance. Their optical properties can meet the requirements of continuous state for broadband background and controllable coupling strength. For example... Figure 2 As shown, the lossy dielectric layer composed of TiN nanoparticles with a diameter of 20-40 nm and a thickness of 60 nm has an effective refractive index (n) in the visible light band between 1.3 and 1.7, which is close to the refractive index of air. This characteristic significantly reduces interfacial Fresnel reflection, allowing most of the incident light to effectively enter the continuous state, thus providing a sufficiently strong broadband interference background for the narrowband resonance of the discrete state. Simultaneously, the extinction coefficient (k) of this layer remains at a low level (0.26-0.55) across the entire visible spectrum, introducing the absorption loss required for the continuous state while avoiding suppression of the discrete state resonance signal due to excessive absorption. This "low reflection, weak absorption" optical characteristic is key to achieving sharp Fano resonance lines.

[0056] The reflection spectrum of this structure was obtained using FDTD optical simulation. Figure 3As shown, this structure exhibits significant selective reflection characteristics in the visible light band, producing a high-intensity reflection peak at approximately 550 nm. Based on the Fano resonance, this structure utilizes the coherent coupling between discrete states (M1D1M2) and continuous states (M2D2) to generate intense destructive interference in the non-resonant region, almost completely suppressing reflection in the blue and red light bands, thus ensuring high-purity output of the structural color. Furthermore, similar spectral profiles can be achieved with four different lossy dielectric layers: TiN, Ti, Ni, and Cr, fully demonstrating the broad applicability of this design scheme to different materials. Further mapping of the reflection spectrum to the CIE 1931 chromaticity diagram (…) Figure 4 Its corresponding color coordinates are distributed in the high saturation region at the edge of the color gamut, which directly verifies the superiority of this structural color in terms of color purity.

[0057] Examples 5-14: Destructive Dielectric Layer Thickness In this embodiment, the overall structural features and preparation method of the high-purity structural color coating based on Fano resonance are as described above. Figure 1 As shown, the coating comprises, from bottom to top, a reflective metal layer M1, a non-destructive dielectric layer D1, a coupling metal layer M2, and a destructive dielectric layer D2. By precisely controlling the geometric parameters of each functional layer, continuous and accurate control of the structural color can be achieved. Key geometric parameters include the thickness of the non-destructive dielectric layer D1, the thickness of the coupling metal layer M2, the thickness of the destructive dielectric layer D2, and the particle size of the nanoparticles within these layers. Optimizing these parameters allows for full color gamut coverage within the visible light range (380-780 nm), and comprehensive control of color brightness, saturation, and bandwidth.

[0058] Considering optical control capabilities, material stability, and process feasibility, in this embodiment, Ag is used for the reflective metal layer M1 and the coupling metal layer M2, SiO2 is used for the non-destructive dielectric layer D1, and TiN nanoparticles are used for the destructive dielectric layer D2. Specifically, the thickness d1 of the reflective metal layer M1 is 100 nm, the thickness d3 of the coupling metal layer M2 is 12 nm, the thickness d2 of the non-destructive dielectric layer D1 is 95-230 nm, the thickness d4 of the destructive dielectric layer D2 is 50 nm, and the diameter distribution of the nanoparticles used ranges from 20-40 nm.

[0059] The only difference between these embodiments 5-14 is the thickness of the non-destructive dielectric layer D1, which is 95nm, 110nm, 125nm, 140nm, 155nm, 170nm, 185nm, 200nm, 215nm, and 230nm, respectively.

[0060] In this embodiment, Ag, SiO2 and TiN are commonly used materials in the field of micro-nano fabrication. Their preparation processes (including spin coating, magnetron sputtering, atomic layer deposition, etc.) are mature technologies with high equipment availability, which can support the large-area, low-cost mass production of the structural color coating on various substrates.

[0061] The overall preparation process is as follows: (1) Substrate pretreatment: Take a 30 mm × 30 mm optical glass substrate, and clean it with acetone, isopropanol, ethanol and deionized water in sequence for 10 min, and then blow it dry for later use.

[0062] (2) Deposition of reflective metal layer M1: The prepared optical glass substrate is fixed on the sample stage of the magnetron sputtering system, and the cavity is evacuated to a base pressure of 8 × 10⁻⁶. -4 Below Pa, high-purity argon gas (20 sccm) was introduced, and the turntable speed was set to 8 r / min. The DC power supply was turned on, and after pre-sputtering Ag (50 W, 10 min, 1.0 Pa), formal sputtering was performed for 5 min to deposit an Ag film with a thickness of approximately 100 nm.

[0063] (3) Deposition of the non-destructive dielectric layer D1: First, a SiO2 precursor solution was prepared, in which the solute was PHPS: 2.9-7.9 wt%, the solvent was dibutyl ether, and 1 wt% APTES was added as a catalyst. The solution was then stirred at 200 rpm until homogeneous, yielding a precursor solution containing PHPS. 300 µL of the above solution was dropped onto the reflective metal layer M1 and allowed to spread naturally under static conditions. Then, it was spin-coated at 3000 rpm for 30 s. The sample was heat-treated on a 120 ℃ hot stage for 20 minutes and cooled to room temperature, finally obtaining a SiO2 layer with a thickness of approximately 95-230 nm.

[0064] (4) Deposit coupling metal layer M2: Using the same magnetron sputtering process as in step 2, the formal sputtering time is adjusted to 40 s to deposit an Ag thin film with a thickness of about 12 nm on the non-destructive dielectric layer D1.

[0065] (5) Deposition of the damaged dielectric layer D2: First, a TiN precursor solution was prepared, in which the solute was TiN nanoparticles: 1.6 wt%, and the solvent was isopropanol and water in a volume ratio of 95:5, with 1 wt% PVP K30 added as a dispersant. The prepared solution was stirred evenly and sonicated for 15 min to obtain a stable TiN nanoparticle precursor solution. Subsequently, a TiN film was prepared on the surface of the coupled metal layer M2 by spin coating. 100 μL of the above precursor solution was dropped onto the surface of the Ag layer and allowed to spread naturally under static conditions. Then, it was spin-coated at 2000 rpm for 30 s to form a wet film. The sample was placed on a 70 ℃ hot stage for 2 minutes and then cooled to room temperature to finally obtain a TiN film with a thickness of approximately 50 nm.

[0066] The TiN precursor solution is obtained by diluting a colloidal TiN solution with a mixture of isopropanol and water. The colloidal TiN solution is a mixture of commercially available TiN ceramic nanoparticles with a size of 20-40 nm and propylene glycol methyl ether acetate, wherein the weight ratio of TiN ceramic nanoparticles is approximately 20%. The specific preparation steps are as follows: ultrasonic pre-dispersing the mixed solvent for 1 hour, followed by high-energy ball milling (the ball milling medium is 5 mm diameter spherical ZrO2, the weight ratio of balls to materials is 20:1, and the milling speed is 700 rpm) for more than 10 hours to obtain a well-dispersed colloidal TiN solution.

[0067] This embodiment verifies the influence of the thickness of the non-destructive dielectric layer D1 on the structural color representation. The thickness of the non-destructive dielectric layer D1 can be precisely controlled by adjusting the concentration of PHPS in the precursor solution (2.9 wt%-7.9 wt%). Figure 5 As shown, under the condition of a fixed spin coating speed of 3000 rpm, there is a good linear relationship between the PHPS concentration and the thickness of the final SiO2 layer.

[0068] The actual color of this structure at different thicknesses of the non-destructive dielectric layer D1 can be determined by examining photographs of the actual object (such as...). Figure 6 As shown in the image, its colors are vibrant and uniformly distributed. Correspondingly, this structure exhibits a continuously tunable spectral response, indicating that the desired color gamut coordinates can be obtained by changing the thickness of the non-destructive dielectric layer D1. Figure 7 As shown, as the thickness of the non-destructive dielectric layer D1 gradually increases from 95 nm to 230 nm, the reflection peak generated by the Fano resonance exhibits a highly regular "redshift" phenomenon, with its peak center wavelength continuously and smoothly shifting from the blue light band to the near-infrared band. During this modulation process, all spectra maintain steep asymmetric line shapes and extremely low substrate reflectance, ensuring that narrow bandwidth and high contrast spectral line shapes can be maintained under full-band modulation.

[0069] Further analysis Figure 8 As shown in the CIE 1931 chromaticity diagram, the chromaticity coordinate trajectory of this structure achieves full coverage of the visible light gamut as the thickness of the lossless dielectric layer D1 increases. The chromaticity coordinates corresponding to all thicknesses are distributed in the high-saturation region at the edge of the gamut, proving that this structure can maintain extremely high color purity in different wavelength bands.

[0070] Comparative Examples 1-5: The overall structure and fabrication process of this comparative example are basically the same as those of Example 5, except that a lossy dielectric layer D2 is not deposited on the surface of the coupling metal layer M2. Instead, a three-layer film structure of "M1D1M2" consisting of a reflective metal layer M1, a lossless dielectric layer D1, and a coupling metal layer M2 is formed. This structure constitutes only the FP resonant cavity, where M1 and M2 serve as the bottom and top reflective surfaces of the resonant cavity, respectively, and D1 is the dielectric layer inside the resonant cavity.

[0071] In this comparative example, Ag is used for the reflective metal layer M1 and the coupling metal layer M2, and SiO2 is used for the lossless dielectric layer D1. The thickness d1 of the reflective metal layer M1 is 100 nm, the thickness d3 of the coupling metal layer M2 is 12 nm, and the thickness d2 of the lossless dielectric layer D1 is 110-190 nm.

[0072] The only difference between Comparative Examples 1-5 is the thickness of the lossless dielectric layer D1, which is 110nm, 130nm, 150nm, 170nm, and 190nm, respectively.

[0073] like Figure 9 As shown, due to the lack of a continuous state formed by the lossy dielectric layer D2, this structure cannot excite the Fano resonance, and its optical response originates entirely from the FP resonance, with the reflection spectrum exhibiting a symmetrical Lorentz line resonance peak. Projecting this spectrum onto the CIE 1931 chromaticity diagram (… Figure 10 As can be seen, its corresponding color coordinates are significantly deviated from the edge of the color gamut, and its color saturation and purity are significantly lower than those of the structures in Examples 5-14.

[0074] This comparative example demonstrates that high-purity structural colors cannot be achieved solely through the "M1D1M2" three-layer FP resonant cavity structure. The lossy dielectric layer D2, composed of nanoparticles, is key to generating Fano resonance and thus achieving high-purity structural colors.

[0075] The above description is only a part of the embodiments of the present invention and does not limit the patent scope of the present invention. All equivalent material and structural changes made under the inventive concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A high-purity structural color coating based on Fano resonance, characterized in that: The coating comprises four layers stacked sequentially from the inside out: M1D1M2D2, where M1 represents a reflective metal layer, D1 represents a lossless dielectric layer, M2 represents a coupling metal layer, and D2 represents a lossy dielectric layer. The lossy dielectric layer D2 is composed of nanoparticles, wherein the three layers of M1D1M2 constitute a discrete structure, and the two layers of M2D2 constitute a continuous structure. The discrete structure and the continuous structure are coupled through the shared coupling metal layer M2, thereby generating a reflective structural color based on Fano resonance.

2. The high-purity structural color coating based on Fano resonance according to claim 1, characterized in that: The materials of the total reflection metal layer M1 and the coupling metal layer M2 are both high-reflectivity materials such as Ag, Au, Al and Cu.

3. The high-purity structural color coating based on Fano resonance according to claim 1, characterized in that: The material of the non-destructive dielectric layer D1 is one of the transparent materials such as TiO2, SiO2, Al2O3, Ta2O5, Nb2O5, HfO2, MgF2, ZnS, Si3N4, LiF and LaTiO3.

4. The high-purity structural color coating based on Fano resonance according to claim 1, characterized in that: The material of the damaged dielectric layer D2 is one or a mixture of multiple nanoparticles such as TiN, W, Mo, V, Fe, Ti, Ni, Si, Cr, Ge, Au, Ag, Al and Cu.

5. The high-purity structural color coating based on Fano resonance according to claim 1, characterized in that: The thickness of the reflective metal layer M1 is 30 nm or more; the thickness of the non-damaging dielectric layer D1 is 1 nm-400 nm; the thickness of the coupling metal layer M2 is 1 nm-60 nm; the thickness of the damaging dielectric layer D2 is 10 nm-100 nm; and the average diameter of the nanoparticles is 10-50 nm.

6. A method for preparing a high-purity structural color coating based on Fano resonance as described in any one of claims 1 to 5, characterized in that: The method is specifically as follows: Step 1: Select a substrate for thin film deposition, and obtain a pretreated substrate after cleaning and processing; Step 2: Prepare the reflective metal layer M1 on the pretreated substrate surface; Step 3: On the surface of the reflective metal layer M1, prepare the non-destructive dielectric layer D1; Step 4: On the surface of the non-destructive dielectric layer D1, prepare the coupling metal layer M2; Step 5: Deposit the damaged dielectric layer D2 on the surface of the coupled metal layer M2 using a solution method.

7. The method for preparing a high-purity structural color coating based on Fano resonance as described in claim 6, characterized in that, The substrate is made of polished glass, polished stainless steel, polished mirror aluminum, polyethylene terephthalate, polyimide, polydimethylsiloxane, polyethylene naphthalate, and polymethyl methacrylate, etc.

8. The method for preparing a high-purity structural color coating based on Fano resonance as described in claim 6, characterized in that, The total reflection metal layer M1, the non-destructive dielectric layer D1, and the coupling metal layer M2 in steps 2-4 are prepared by one of the following methods: spin coating, spray coating, scraping coating, brush coating, physical vapor deposition, and chemical vapor deposition.

9. The method for preparing a high-purity structural color coating based on Fano resonance as described in claim 6, characterized in that, The method for preparing the damaged dielectric layer D2 in step 5 is a solution method, including one of the following solutions: spin coating, spray coating, blade coating, brush coating, and flow coating. Specifically, the solution method involves applying a dispersion containing the nanoparticles onto the surface of the coupled metal layer M2.

10. The application of the high-purity structural color coating according to any one of claims 1-5 or the high-purity structural color coating prepared by the preparation method according to any one of claims 6-9, characterized in that, Applications include, but are not limited to, display devices, decorative coatings, and anti-counterfeiting labels.

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