Optothermally regulated multilayer film and method of making the same

Abstract

The application provides a photothermal regulation multilayer film and a preparation method thereof, and belongs to the technical field of optical films. The film comprises, from bottom to top, a fourth film layer, a third film layer, a second film layer and a first film layer which are sputter-deposited on the surface of a graphite substrate in sequence. The first film layer and the second film layer are used for realizing visible light structural color regulation and mechanical protection, the third film layer is used for realizing directional radiation of a target angle in a medium-long infrared wave band, and the fourth film layer forms a Fabry-Perot resonant cavity together with the third film layer, the second film layer and the first film layer to regulate the wave absorption performance of the overall film in the medium-long infrared wave band. The photothermal regulation multilayer film successfully realizes the organic coupling of mechanical protection, visible light structural color regulation, medium-long infrared directional radiation and radiation heat dissipation.

Description

Technical Field

[0001] This invention relates to the field of optical thin film technology, and in particular to a photothermal modulated multilayer thin film and its preparation method. Background Technology

[0002] With the rapid development of optical sensing, thermal imaging and environmental monitoring technologies, outdoor fixed facilities (such as wildlife observation stations and communication relay stations) have put forward higher requirements for multifunctional surface integration. Developing multispectral compatible surface technologies that can coordinate visible light structural color regulation, directional infrared thermal radiation regulation and mechanical protection has become an important frontier in the fields of optical materials, thermal management and surface engineering.

[0003] However, current technologies have significant limitations in achieving functionality across various wavelengths and are difficult to effectively integrate. In visible light structured color modulation, they generally rely on pigment coatings, which have fixed colors, poor adaptability, and lack infrared thermal radiation management capabilities. While structured color technologies based on photonic crystals or multilayer thin-film interference can achieve dynamic color adjustment, they typically require multilayer periodic structures, leading to increased thickness, angle sensitivity, and poor wide-band responsiveness. Furthermore, they are often accompanied by strong mid- and far-infrared absorption, disrupting the target's infrared thermal radiation management characteristics.

[0004] In the manipulation of infrared thermal radiation, low-emissivity metal thin films (such as aluminum and gold) or filler coatings are typically used to reduce the temperature difference with the background by reflecting ambient thermal radiation and suppressing their own radiation. However, the low emissivity of these coatings hinders radiative heat dissipation, easily leading to heat accumulation and the formation of "hot spots." Furthermore, their uniform Lambertian radiation characteristics make them easily detectable. Meanwhile, research on directional thermal radiation often focuses on a single infrared band, resulting in complex structures that are frequently based on noble metals or two-dimensional metasurfaces requiring precise photolithography, making effective physical and technological integration with visible light manipulation structures difficult. In terms of mechanical protection, surface hardness is often improved by introducing hardness-enhancing thin film materials (such as AlN, TiO2, and DLC). However, the optical properties of these materials in the visible and mid-to-long infrared bands conflict with the structural color design and infrared transmission requirements of the visible light band. In addition, thin films prepared by conventional processes lack sufficient density and have limited erosion resistance, making it difficult to maintain stable optical performance in harsh environments such as sandstorms.

[0005] Therefore, there is an urgent need to provide a photothermal modulated multilayer thin film and its preparation method. Summary of the Invention

[0006] This invention provides a photothermal modulated multilayer thin film and its preparation method, which can solve the problem that existing thin film materials cannot simultaneously achieve visible light structural color modulation, infrared directional thermal radiation, and surface mechanical protection.

[0007] In a first aspect, the present invention provides a photothermal modulated multilayer thin film, comprising a fourth thin film layer, a third thin film layer, a second thin film layer, and a first thin film layer sequentially sputtered and deposited on the surface of a graphite substrate from bottom to top; wherein, the first thin film layer and the second thin film layer are used to achieve visible light structural color modulation and mechanical protection, the third thin film layer is used to achieve directional radiation of a target angle in the mid-to-long infrared band, and the fourth thin film layer, the third thin film layer, the second thin film layer, and the first thin film layer form a Fabry-Perot resonant cavity to modulate the overall absorption performance of the thin film in the mid-to-long infrared band.

[0008] Preferably, the target angle is 70°~85°; the material of the first thin film layer satisfies the following conditions: hardness greater than 10 GPa, and extinction coefficient tending to 0 in the visible light band and the mid-to-long infrared band, and refractive index tending to 1 in the mid-to-long infrared band.

[0009] Preferably, the material of the second thin film layer satisfies the following conditions: the extinction coefficient in the visible light band and the mid-to-long infrared band tends to be 0, and the refractive index in the visible light band is greater than the refractive index of the material of the first thin film layer.

[0010] Preferably, the material of the third thin film layer satisfies the following conditions: the extinction coefficient in the mid-to-long infrared band tends to be 0, and the refractive index in the mid-to-long infrared band can achieve optical matching of the target angle Brewster angle.

[0011] Preferably, the material of the fourth thin film layer satisfies the following conditions: the extinction coefficient in the mid-to-long infrared band tends to be 0, and it matches the optical admittance of the third thin film layer in the mid-to-long infrared band.

[0012] Preferably, the material of the first thin film layer is either aluminum oxide or aluminum nitride.

[0013] Preferably, the material of the second thin film layer is either silicon or gallium arsenide.

[0014] Preferably, the material of the third thin film layer is one of germanium or zinc sulfide.

[0015] Preferably, the fourth thin film layer material is either aluminum oxide or silicon monoxide.

[0016] Preferably, when the first thin film layer material is aluminum oxide, the thickness is 50~350nm; when the first thin film layer material is aluminum nitride, the thickness is 150~300nm.

[0017] When the second thin film layer material is silicon, the thickness is 70~130nm; when the second thin film layer material is gallium arsenide, the thickness is 60~140nm.

[0018] When the third thin film material is germanium, the thickness is 500~700nm; when the third thin film material is zinc sulfide, the thickness is 250~550nm.

[0019] When the fourth thin film material is aluminum oxide, the thickness is 350~450nm; when the fourth thin film material is silicon monoxide, the thickness is 250~450nm.

[0020] More preferably, the first thin film layer material is aluminum oxide; the second thin film layer material is silicon; the third thin film layer material is germanium; and the fourth thin film layer material is aluminum oxide.

[0021] Secondly, embodiments of the present invention also provide a method for preparing the photothermal regulated multilayer thin film according to any one of the first aspects, the method comprising:

[0022] Using the constructive interference of the target structural color in the visible light band as the initial constraint, and combining the material's hardness and optical properties in the visible and mid-to-long infrared bands, the material and thickness range of the first thin film layer are screened and determined from the candidate materials.

[0023] The material of the second thin film layer is selected and determined based on the optical properties of the first thin film layer material, so that the first thin film layer and the second thin film layer form a double-layer interference structure to jointly regulate the visible light structural color.

[0024] Based on the optical properties of the first and second thin film layer materials in the mid- and long-infrared bands, and the Brewster angle requirement at the target angle, the third thin film layer material was screened and determined.

[0025] Based on the optical properties of the first, second, and third thin film layer materials in the mid- and long-infrared bands, the fourth thin film layer material was screened and determined so that the four thin films could form a Fabry-Perot resonant cavity structure.

[0026] An optical simulation model of a multilayer thin film was constructed, and the thickness of each thin film layer was determined by multiphysics simulation. Then, radio frequency magnetron sputtering was used to deposit each thin film layer sequentially on the surface of a graphite substrate to prepare the photothermal regulated multilayer thin film.

[0027] Preferably, the optical properties include extinction coefficient and refractive index.

[0028] Preferably, the candidate material is one of Al2O3, AlN, TiO2, or diamond-like carbon.

[0029] Preferably, the thickness range of the first thin film layer is determined by the following formula:

[0030]

[0031] In the formula, d The thickness of the first thin film layer material. m It is a positive integer. λ For wavelength, nThe refractive index of the first thin film layer material is . The target angle for directional radiation.

[0032] Preferably, the power of the radio frequency magnetron sputtering is 70~120W and the gas pressure is 0.5~1.0Pa; the sputtering gas includes at least one of oxygen or argon.

[0033] Preferably, the second thin film layer is prepared by radio frequency magnetron sputtering combined with bias voltage; wherein the sputtering power is 70~90W, the gas pressure is 0.5~0.8Pa, and the bias voltage is -22~-18V.

[0034] More preferably, the first thin film layer is deposited sequentially by radio frequency magnetron sputtering under both unbiased and biased conditions; wherein the sputtering power is 90~110W, the gas pressure is 0.5~0.8Pa, and the bias is -85~-75V; the thickness of the film layer deposited under unbiased conditions is 15~20nm.

[0035] Compared with the prior art, the present invention has at least the following beneficial effects:

[0036] The multifunctional coupled photothermal control film of this invention, by abandoning the traditional complex superstructure and simplifying the types and number of film layers, is formed only by a fourth film layer, a third film layer, a second film layer, and a first film layer arranged sequentially from top to bottom. This fundamentally avoids problems such as interlayer stress mismatch, interface loss, and thermal expansion incompatibility. The first film layer is an integrated functional layer that works in conjunction with the second film layer. By adjusting its own thickness, it can achieve wide color gamut visible light structural color control. Furthermore, this layer uses a high-hardness material and is strengthened through a specific process, endowing the film with excellent strength. The third thin film layer not only enables directional radiation over a high-angle range in the mid-to-long infrared band, thus achieving directional control of infrared signals and effectively reducing the risk of detection and identification by external detectors, but also exhibits high emissivity characteristics across all angles, ensuring efficient heat dissipation, thereby achieving a unity of infrared stealth and radiative heat dissipation. The fourth thin film layer, together with the third, second, and first thin film layers, forms a Fabry-Perot resonant cavity, thereby controlling the overall absorption performance of the thin film in the mid-to-long infrared band. Ultimately, this allows the thin film to successfully achieve the organic coupling of mechanical protection, visible light structural color control, and mid-to-long infrared directional radiation and radiative heat dissipation. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the overall structure of a photothermal modulated multilayer thin film provided in an embodiment of the present invention;

[0039] Figure 2 A color gamut map obtained from the simulation of a photothermal modulated multilayer thin film is provided in an embodiment of the present invention;

[0040] Figure 3 The thermal radiation diagrams of a photothermally modulated multilayer thin film with a first thin film layer thickness of 210 nm at different angles in the 3-14 μm band are provided in an embodiment of the present invention.

[0041] Figure 4 The thermal radiation diagrams of a photothermally modulated multilayer thin film with a first thin film layer thickness of 350 nm at different angles in the 3-14 μm band are provided in an embodiment of the present invention.

[0042] Figure 5 This is a graph showing the overall hardness variation of the first film layer in a photothermally modulated multilayer film under different thicknesses, as provided in an embodiment of the present invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0044] As mentioned above, in order to solve the problem that existing thin films cannot achieve multifunctional coupling of visible light structure control, infrared directional radiation, and surface mechanical protection, this invention provides a photothermal modulated multilayer thin film. The thin film includes a fourth thin film layer, a third thin film layer, a second thin film layer, and a first thin film layer, which are sequentially sputtered and deposited on the surface of a graphite substrate from bottom to top. The first thin film layer and the second thin film layer are used to achieve visible light structure color control and mechanical protection. The third thin film layer is used to achieve directional radiation at a target angle in the mid-to-long infrared band. The fourth thin film layer, the third thin film layer, the second thin film layer, and the first thin film layer form a Fabry-Perot resonant cavity to control the absorption performance of the overall thin film in the mid-to-long infrared band.

[0045] The multifunctional coupled photothermal control film in this embodiment of the invention, by abandoning the traditional complex superstructure and simplifying the types and number of film layers, is formed only by a fourth film layer, a third film layer, a second film layer, and a first film layer arranged sequentially from top to bottom. This fundamentally avoids problems such as interlayer stress mismatch, interface loss, and thermal expansion incompatibility. The first film layer is an integrated functional layer that works in conjunction with the second film layer. By adjusting its own thickness, it can achieve wide color gamut visible light structural color control. Furthermore, this layer uses a high-hardness material and is strengthened through a specific process, endowing the film with excellent... The first thin film layer provides excellent mechanical protection. The third thin film layer not only enables directional radiation over a high-angle range in the mid-to-long infrared band, thus allowing for directional control of infrared signals and effectively reducing the risk of detection by external detectors, but also exhibits high emissivity across all angles, ensuring efficient heat dissipation, thereby achieving a balance between infrared stealth and radiative heat dissipation. The fourth thin film layer, together with the third, second, and first thin film layers, forms a Fabry-Perot resonant cavity, thereby controlling the overall absorption performance of the thin film in the mid-to-long infrared band. Ultimately, this allows the thin film to successfully achieve the organic coupling of mechanical protection, visible light structural color control, and mid-to-long infrared directional radiation and radiative heat dissipation.

[0046] According to some preferred embodiments, the target angle is 70°~85°; the material of the first thin film layer satisfies the following conditions: hardness greater than 10 GPa, and extinction coefficient tending to 0 in the visible light band and the mid-to-long infrared band, and refractive index tending to 1 in the mid-to-long infrared band; the material of the second thin film layer satisfies the following conditions: extinction coefficient tending to 0 in the visible light band and the mid-to-long infrared band, and refractive index in the visible light band greater than the refractive index of the first thin film layer; the material of the third thin film layer satisfies the following conditions: extinction coefficient tending to 0 in the mid-to-long infrared band, and refractive index in the mid-to-long infrared band capable of optically matching the Brewster angle of the target angle; the material of the fourth thin film layer satisfies the following conditions: extinction coefficient tending to 0 in the mid-to-long infrared band, and matching the optical admittance of the third thin film layer in the mid-to-long infrared band.

[0047] In this embodiment of the invention, the first thin film layer is made of a material that simultaneously satisfies the above-mentioned hardness and optical properties conditions. This not only ensures that the top thin film has excellent mechanical protection, but also ensures high interference, high contrast and high color purity of the structural color. At the same time, it can form a transparent window in the mid- and long-infrared band, ensuring that mid- and long-infrared light can be transmitted without absorption. Furthermore, its refractive index in the mid- and long-infrared band is adapted to the Brewster angle of the lower thin film and matched with other thin film layers to construct a Fabry-Perot resonant cavity, which is beneficial for the thin film to achieve high-angle directional radiation in the mid- and long-infrared band. The extinction coefficient of the second thin film layer is the same as that of the first thin film layer in both wavelength bands, and its refractive index is greater than that of the first thin film layer. This allows for strong reflection, forming a double-layer thin film interference structure with the first thin film layer, further enhancing the precision of visible light structural color modulation. The third and fourth thin film layers use materials with extinction coefficients approaching zero in the mid-to-long infrared band, ensuring no absorption loss during transmission of mid-to-long infrared light between the two layers, guaranteeing directional radiation in the mid-to-long infrared band. Furthermore, the optical admittance of the two layers in the mid-to-long infrared band is matched, which is beneficial for ensuring that the fourth thin film layer forms a Fabry-Perot resonator structure with the other thin film layers, achieving overall mid-to-long infrared absorption performance modulation. Thus, by limiting the materials of each thin film layer to the above conditions, it is beneficial to achieve precise performance adaptation and functional synergy between the thin film layers, thereby facilitating the functional coupling of mechanical protection, visible light structural color modulation, and mid-to-long infrared directional radiation in multilayer thin films.

[0048] According to some preferred embodiments, the first thin film layer material is one of aluminum oxide or aluminum nitride; the second thin film layer material is one of silicon or gallium arsenide; the third thin film layer material is one of germanium or zinc sulfide; and the fourth thin film layer material is one of aluminum oxide or silicon monoxide.

[0049] According to some preferred embodiments, when the first thin film layer material is aluminum oxide, the thickness is 50~350nm (e.g., it can be 50nm, 100nm, 150nm, 210nm, 230nm, 250nm, 270nm, 290nm, 330nm or 350nm); when the first thin film layer material is aluminum nitride, the thickness is 150~300nm (e.g., it can be 150nm, 200nm, 250nm or 300nm); when the second thin film layer material is silicon, the thickness is 70~130nm (e.g., it can be 70nm, 80nm, 90nm, 100nm, 110nm, 120nm or 130nm); when the second thin film layer material is gallium arsenide, the thickness is 60~140nm (e.g., it can be 60nm, 80nm, ...). The thickness of the third thin film layer is 500-700 nm (e.g., 500 nm, 550 nm, 600 nm, 650 nm, or 700 nm) when the third thin film layer material is germanium; the thickness of the fourth thin film layer material is 250-550 nm (e.g., 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or 550 nm) when the third thin film layer material is zinc sulfide; the thickness of the fourth thin film layer material is 350-450 nm (e.g., 350 nm, 400 nm, or 450 nm) when the fourth thin film layer material is aluminum oxide; and the thickness of the fourth thin film layer material is 250-450 nm (e.g., 250 nm, 300 nm, 350 nm, 400 nm, or 450 nm) when the fourth thin film layer material is silicon monoxide.

[0050] To achieve multispectral functional integration, related technologies typically rely on embedding complex micro / nano structures within multilayer film systems. This not only leads to excessively large total film thickness and increased interlayer interfaces, increasing deposition time and cost, but also introduces significant problems such as interlayer stress mismatch, increased interface scattering loss, and incompatible thermal expansion coefficients. Furthermore, complex film systems have extremely stringent requirements for the process tolerance of nanoscale layer thickness; even minor deviations can lead to simultaneous degradation of performance across multiple wavelength bands, severely restricting manufacturing yield and reliability. Therefore, in this embodiment of the invention, materials for each layer are precisely selected from commonly used optical thin film materials to ensure they meet the optical characteristics of each layer. Moreover, the selected materials are all compatible with sputtering deposition processes and possess excellent interlayer adhesion and thermal expansion coefficient compatibility, resulting in low film fabrication difficulty and good process repeatability. In addition, through the synergistic design of optical admittance and electromagnetic loss for each film, redundant thickness is reserved for each layer, effectively offsetting experimental errors during fabrication and ensuring a high degree of consistency between actual performance and theoretical design.

[0051] According to some preferred embodiments, the first thin film layer material is aluminum oxide; the second thin film layer material is silicon; the third thin film layer material is germanium; and the fourth thin film layer material is aluminum oxide.

[0052] In this embodiment of the invention, when the materials of each thin film layer are preferably the above-mentioned combination, multiple functions of the thin film can be integrated by constructing four thin films with only three materials. The above-mentioned material combination not only enables the optical and mechanical properties of each thin film layer material to match each other, but also has excellent process compatibility, good interlayer adhesion and mutually coordinated thermal expansion coefficients. This effectively avoids problems such as stress mismatch, scattering loss and thermal mismatch introduced by heterogeneous material stacking and multiple interfaces. The unity of optical performance, mechanical protection and process performance can be achieved with only four-layer structure.

[0053] This invention also provides a method for preparing the photothermal modulated multilayer thin film according to any one of the above claims, the method comprising:

[0054] Using the constructive interference of the target structural color in the visible light band as the initial constraint, and combining the material's hardness and optical properties in the visible and mid-to-long infrared bands, the material and thickness range of the first thin film layer are screened and determined from the candidate materials.

[0055] The material of the second thin film layer is selected and determined based on the optical properties of the first thin film layer material, so that the first thin film layer and the second thin film layer form a double-layer interference structure to jointly regulate the visible light structural color.

[0056] Based on the optical properties of the first and second thin film layer materials in the mid- and long-infrared bands, and the Brewster angle requirement at the target angle, the third thin film layer material was screened and determined.

[0057] Based on the optical properties of the first, second, and third thin film layer materials in the mid- and long-infrared bands, the fourth thin film layer material was screened and determined so that the four thin films could form a Fabry-Perot resonant cavity structure.

[0058] An optical simulation model of a multilayer thin film was constructed, and the thickness of each thin film layer was determined by multiphysics simulation. Then, radio frequency magnetron sputtering was used to deposit each thin film layer sequentially on the surface of a graphite substrate to prepare the photothermal regulated multilayer thin film.

[0059] According to some preferred embodiments, the optical properties include extinction coefficient and refractive index; the candidate material is one of Al2O3, AlN, TiO2 or diamond-like carbon.

[0060] In this embodiment of the invention, by precisely selecting the material of the first thin film layer, the independent color layer, protective layer, and infrared window layer are integrated into a single film layer. Firstly, based on the physical principle of thin film interference, the constructive interference condition for the target color in the visible light band (380~780nm) is used as a constraint. Secondly, the hardness of the material and its optical properties (refractive index) in the visible and mid-to-long infrared bands are considered. nThe first thin film layer material is selected from candidate materials based on the extinction coefficient (k). Specifically, during the selection process, the hardness of the first thin film layer material must be higher than 10 GPa to ensure good mechanical protection. Furthermore, it must have a low refractive index and an extinction coefficient close to 0 in the visible light band to ensure high interference contrast and high-purity structural color. Additionally, it must have a low extinction coefficient in the mid-to-long infrared band to form a low-loss optically transparent window. Further, its refractive index in the mid-to-long infrared band must approach 1 to meet the Brewster angle construction requirements at high target angles (70°~85°). The material selected under these conditions can form a multifunctional integrated top layer, which not only possesses excellent mechanical protection against external wear, but also allows direct control of the visible light structural color through thickness adjustment. Simultaneously, it can form a Fabry-Perot resonator with the Brewster angle selective layer of the lower thin film, enabling directional radiation in the mid-to-long infrared band.

[0061] According to some preferred embodiments, the material of the second thin film layer satisfies the following conditions: the extinction coefficient in the visible light band and the mid-to-long infrared band tends to be 0, and the refractive index in the visible light band is greater than the refractive index of the first thin film layer.

[0062] The material of the third thin film layer satisfies the following conditions: the extinction coefficient in the mid- and long-infrared band approaches 0, and the refractive index in the mid- and long-infrared band can achieve optical matching of the target angle Brewster angle.

[0063] The material of the fourth thin film layer satisfies the following condition: the extinction coefficient in the mid-to-long infrared band tends to be 0, and it matches the optical admittance of the third thin film layer in the mid-to-long infrared band.

[0064] To achieve directional thermal radiation in the mid-to-long-wave infrared, a sophisticated Fabry-Perot resonator is typically constructed, whose resonance characteristics are extremely sensitive to the optical length within the cavity. In traditional schemes, the top thin film used to modulate the visible light structural color is part of the resonator; changes in its thickness directly alter the cavity's optical length, causing shifts in the center wavelength, intensity, and directionality of the infrared emission peak. Furthermore, this layer material must simultaneously meet the requirements of visible light admittance matching and low loss in the mid-to-long-wave infrared, making independent control of visible light color modulation and infrared radiation extremely difficult.

[0065] To address the aforementioned issues, this invention employs a progressive material selection method, ensuring precise functional matching of each layer. Specifically, the second thin film layer, based on the optical characteristics of the first thin film layer, selects materials with extinction coefficients approaching zero in the visible and mid-to-long infrared bands and higher refractive indices in the visible band. These materials can form a double-layer interference structure with the first thin film layer, achieving high-purity structural color. The third thin film layer, based on the optical characteristic parameters of the second thin film layer, selects materials with both high transmittance and Brewster angle directional radiation characteristics in the mid-to-long infrared band. Its refractive index matches that of the upper thin film layer. Based on Brewster's law, the refractive index range that allows p-polarized infrared light to pass through the material with near-non-reflective properties at the target angle (e.g., 70°~85°) can be calculated, thereby achieving directional control of infrared radiation at the target angle. The fourth thin film layer, based on the optical admittance matching of the third thin film layer, forms a Fabry-Perot resonant cavity in conjunction with the first three layers. By parameterizing the cavity thickness, the emissivity characteristics of the thin film in the mid-to-long infrared band can be controlled, thereby managing the infrared absorption performance. In this way, the visible light structural color can be independently adjusted by adjusting the thickness of the first thin film layer, and it can be completely decoupled from the mid- and long-infrared directional radiation and absorption modulation functions.

[0066] According to some preferred embodiments, the thickness range of the first thin film layer is determined by the following formula:

[0067]

[0068] In the formula, d The thickness of the first thin film layer material. m It is a positive integer. λ For wavelength, n The refractive index of the first thin film layer material is . The target angle for directional radiation.

[0069] In this embodiment of the invention, the first thin film layer serves as the core layer for visible light structural color modulation. Its thickness is determined based on the physical principles of thin film interference, constrained by the constructive interference condition for the target color in the visible light band (380~780nm). The thickness range of different candidate materials to achieve the target structural color is calculated using the aforementioned formula. Based on this, an optical simulation model of the multilayer thin film is constructed according to the determined multilayer thin film materials. Using the thickness range of the first thin film layer as a basis, and the thicknesses of other thin film layers as variables, parametric scanning and multiphysics simulation are performed to simulate and evaluate the overall optical characteristics of thin films with different thickness combinations. The optimization goal is to maximize the visible light color gamut coverage and infrared emissivity. The thickness range of each thin film layer is determined, thus ensuring the compatibility of optical performance between each thin film layer. Furthermore, by adjusting the thickness of the first thin film layer, a wide color gamut and high-purity structural color can be achieved without interfering with the optical performance in the mid-to-long infrared band.

[0070] According to some preferred embodiments, the power of the radio frequency magnetron sputtering is 70~120W (e.g., 70W, 80W, 90W, 100W, 110W or 120W), and the gas pressure is 0.5~1.0Pa (e.g., 0.5Pa, 0.6Pa, 0.7Pa, 0.8Pa, 0.9Pa or 1.0Pa); the sputtering gas of the radio frequency magnetron sputtering includes at least one of oxygen or argon.

[0071] In this embodiment of the invention, the process parameters used in the sputtering process differ for different thin film layers. According to some specific implementation methods, when preparing the fourth thin film layer, the target material is selected as Al2O3 or SiO, the sputtering gas is argon and oxygen, the argon flow rate is 25-35 sccm, the oxygen flow rate is 0.3-0.8 sccm, the sputtering power is 90-110 W, the sputtering pressure is 0.8-1.0 Pa, and the pre-sputtering time is 5-10 min; when preparing the third thin film layer, the target material is selected as Ge or ZnS, the sputtering gas is argon, the argon flow rate is 25-35 sccm, the sputtering power is 100-120 W, the sputtering pressure is 0.8-1.0 Pa, and the pre-sputtering time is 5-10 min; when preparing the fourth thin film layer... For the second thin film layer, the target material is Si or GaAs, the sputtering gas is argon, the argon flow rate is 25~35 sccm, the sputtering power is 70~90W, the sputtering pressure is 0.5~0.8Pa, the pre-sputtering time is 5~10min, and a bias voltage of -22~-18V is applied. When preparing the first thin film layer, the target material is Al2O3 or AlN, the sputtering gas is argon and oxygen, the argon flow rate is 25~35 sccm, the oxygen flow rate is 0.3~0.8 sccm, the sputtering power is 90~110W, the sputtering pressure is 0.5~0.8Pa, the pre-sputtering time is 5~10min, first sputtering to a certain thickness under non-bias conditions, and then sputtering to the target thickness under a bias voltage of -85~-75V.

[0072] According to some preferred embodiments, the second thin film layer is prepared by radio frequency magnetron sputtering combined with bias voltage; wherein the sputtering power is 70~90W (e.g., 70W, 80W or 90W), the gas pressure is 0.5~0.8Pa (e.g., 0.5Pa, 0.6Pa, 0.7Pa or 0.8Pa), and the bias voltage is -22~-18V (e.g., -18V, -20V or -22V).

[0073] According to some preferred embodiments, a first thin film layer is deposited sequentially by radio frequency magnetron sputtering under both unbiased and biased conditions; wherein the sputtering power is 90~110W (e.g., 90W, 100W or 110W), the gas pressure is 0.5~0.8Pa (e.g., 0.5Pa, 0.6Pa, 0.7Pa or 0.8Pa), and the bias voltage is -85~-75V (e.g., -75V, -80V or -85V); under this deposition method, the thickness of the film layer deposited under unbiased conditions is preferably 15~20nm (e.g., 15nm, 16nm, 17nm, 18nm, 19nm or 20nm).

[0074] To achieve visible light structural color modulation based on thin-film interference, it is usually necessary to precisely control the thickness of the outermost thin film at the subwavelength scale. However, this contradicts the requirement for effective mechanical protection, which requires a thickness of more than 100 nanometers and a highly dense and robust microstructure. Specifically, a thin film that simply meets the conditions for wide color gamut interference in visible light may be too thin to provide effective protection, while simply increasing the thickness or using high-energy processes to enhance the film thickness will lead to a decrease in both optical and mechanical properties due to microstructure degradation or reverse damage to the formed optical structure layer by high-energy particles. To address the aforementioned issues, this invention employs a method combining radio frequency magnetron sputtering with radio frequency bias on the substrate to prepare the first thin film layer. First, a homogeneous layer of a certain thickness is sputtered and deposited under non-biased conditions. Then, a radio frequency bias is independently applied to the substrate, creating a negative potential on its surface. Under these conditions, the same material continues to be deposited. During this process, while high-energy particles densify the thin film to form a high-hardness protective layer, their etching effect primarily acts on the pre-deposited homogeneous layer. This effectively reduces the etching of other thin film layers and avoids the introduction of excessively high defect density, unfavorable internal stress, and additional optical losses, achieving a balance between optical and mechanical protective properties within a single thin film layer.

[0075] To more clearly illustrate the technical solution and advantages of the present invention, the following examples provide a detailed description of a photothermal modulated multilayer thin film and its preparation method.

[0076] Example 1

[0077] The structure and thickness of the thin film were determined by screening and simulation using the above method, such as Figure 1 As shown, the thin film is arranged sequentially from the incident surface to the substrate (graphite): first thin film layer (Al2O3 with thicknesses of 210nm, 230nm, 250nm, 270nm, 290nm, 330nm, and 350nm respectively), second thin film layer (Si with a thickness of 100nm), third thin film layer (Ge with a thickness of 600nm), and fourth thin film layer (Al2O3 with a thickness of 400nm).

[0078] The graphite substrate was polished and ultrasonically cleaned three times in 99.99% alcohol. After drying, the cleaned substrate was fixed onto the workpiece disk. A vacuum was then created in the deposition chamber using a molecular pump to achieve a vacuum level of ≤5×10⁻⁶. -4 Pa; Introduce high-purity argon gas to a starting pressure of 3~5Pa, adjust the gas pressure to 0.5~1Pa after pre-sputtering, turn on the protective substrate baffle, turn on the stepper motor, and keep the workpiece disk speed at 5rpm / min;

[0079] Adjust the RF power supply to 100W, argon gas to 30sccm, oxygen gas to 0.5sccm, sputtering pressure to 1Pa, and start the power supply. The Al2O3 target material is ignited for pre-sputtering for 10 minutes. Then open the baffle and start the formal deposition. According to the film thickness gauge, the fourth film thickness is sputtered to the target of 400nm. After the deposition thickness is reached, close the baffle and turn off the target power supply.

[0080] Switch the RF power supply to the Ge target, adjust the sputtering power to 110W, use argon gas at 30sccm, and pre-sputter at a sputtering pressure of 1.0Pa for 5 minutes. Then open the baffle and begin the formal deposition. According to the film thickness gauge, sputter the third film thickness to the target of 600nm. After reaching the deposition thickness, close the baffle and turn off the target power supply.

[0081] Switch the RF power supply to the Si target, adjust the sputtering power to 80W, use argon gas at 30sccm, sputtering pressure at 0.5Pa for 5 minutes of pre-sputtering, and bias voltage at -20V. Then open the baffle and begin formal deposition. According to the film thickness gauge, sputter the second film thickness to the target of 100nm. After reaching the deposition thickness, close the baffle and turn off the target power supply.

[0082] Switch the RF power supply to the Al2O3 target, adjust the sputtering power to 100W, use argon gas at 30 sccm, oxygen gas at 0.5 sccm, and pre-sputter at a sputtering pressure of 1.0 Pa for 6 minutes. First, deposit a homogeneous layer of 15 nm under non-bias conditions (the thickness of the homogeneous layer was determined by microscopic and hardness tests). Then, under a bias of -80V, according to the film thickness gauge, the overall thickness of the first thin film layer was sputtered to the target thickness of 210~350 nm. After reaching the deposition thickness, turn off the baffle and the target power supply to obtain a photothermally regulated multilayer thin film.

[0083] Example 2

[0084] Example 2 is basically the same as Example 1, taking a first thin film layer thickness of 350 nm as an example. The difference lies in the preparation of the second and first thin film layers as follows:

[0085] Switch the RF power supply to the Si target, adjust the sputtering power to 80W, use argon gas at 30sccm, and pre-sputter at a sputtering pressure of 0.5Pa for 5 minutes. Then open the baffle and begin the formal deposition. According to the film thickness gauge, sputter the second film thickness to the target of 100nm. After reaching the deposition thickness, close the baffle and turn off the target power supply.

[0086] Switch the RF power supply to the Al2O3 target, adjust the sputtering power to 100W, use argon gas at 30 sccm, oxygen gas at 0.5 sccm, and a sputtering pressure of 1.0 Pa for 6 minutes of pre-sputtering. According to the film thickness gauge, the overall thickness of the first thin film layer is sputtered and deposited to the target thickness of 350 nm. After the deposition thickness is reached, turn off the baffle and the target power supply to obtain a photothermal regulated multilayer thin film.

[0087] The performance of the photothermal modulated multilayer thin film prepared in Example 1 was tested. Figure 2 As can be seen, by varying the thickness of the first thin film layer (Al2O3) within the range of 210 nm to 350 nm, the simulated color gamut (X: 0.18-0.4; Y: 0.2-0.46) is widely covered. Furthermore, the colors of the fabricated multilayer films match the simulated color gamut at the corresponding thicknesses: orange at 210 nm, pink at 230 nm, purple at 250 nm, blue at 270 nm, cyan at 290 nm, green at 330 nm, and yellow at 350 nm. This demonstrates that the visible light structural color can be precisely controlled by adjusting the thickness of the first thin film layer. Figure 3 and Figure 4 As shown, in terms of infrared performance, variations in the thickness of the first thin film layer have almost no effect on the emissivity distribution in the 3-14 μm band. In the mid-infrared band (3-5 μm) and the long-infrared band (8-14 μm), the multilayer film exhibits significant directional emission characteristics at high angles of 70°-85°, and the normal emissivity at the detector center wavelengths (e.g., 4 μm and 10.6 μm) is as low as 0.14 and 0.19, respectively, significantly reducing the risk of being detected by the detector. Simultaneously, it exhibits high emissivity across the entire angular range in the 5-8 μm non-atmospheric window band, effectively promoting radiative heat dissipation, thus synergistically achieving directional infrared radiation and efficient heat dissipation. Figure 5 As shown, in terms of mechanical properties, the hardness of the film increases with the increase of the thickness of the first film layer, from 13.5 GPa at 210 nm to 15.6 GPa at 350 nm (the hardness of the multilayer film in Example 2 is only 7 GPa), and finally realizes the coupling of mechanical protection, visible light structural color regulation and infrared thermal management.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A photothermal modulated multilayer thin film, characterized in that, The thin film comprises a fourth thin film layer, a third thin film layer, a second thin film layer, and a first thin film layer, sequentially sputtered and deposited on the surface of a graphite substrate from bottom to top. The first and second thin film layers are used for visible light structural color modulation and mechanical protection. The third thin film layer is used for directional radiation at a target angle in the mid-to-long infrared band. The fourth, third, second, and first thin film layers form a Fabry-Perot resonant cavity to modulate the overall absorption performance of the thin film in the mid-to-long infrared band. The target angle is 70°~85°. The material of the first thin film layer satisfies the following conditions: hardness greater than 10 GPa, and extinction coefficient tending to 0 in the visible light band and the mid-to-long infrared band, and refractive index tending to 1 in the mid-to-long infrared band. The material of the second thin film layer satisfies the following conditions: the extinction coefficient in the visible light band and the mid-to-long infrared band tends to be 0, and the refractive index in the visible light band is greater than the refractive index of the material of the first thin film layer. The material of the third thin film layer satisfies the following conditions: the extinction coefficient in the mid- and long-infrared band approaches 0, and the refractive index in the mid- and long-infrared band can achieve optical matching of the target angle Brewster angle. The material of the fourth thin film layer satisfies the following conditions: the extinction coefficient in the mid- and long-infrared band approaches 0, and it matches the optical admittance of the third thin film layer in the mid- and long-infrared band. The first thin film layer material is either aluminum oxide or aluminum nitride; The second thin film layer material is either silicon or gallium arsenide; The third thin film layer material is either germanium or zinc sulfide; The fourth thin film layer material is either aluminum oxide or silicon monoxide.

2. The photothermal regulated multilayer thin film according to claim 1, characterized in that, When the first thin film layer material is aluminum oxide, the thickness is 50~350nm; when the first thin film layer material is aluminum nitride, the thickness is 150~300nm. When the second thin film layer material is silicon, the thickness is 70~130nm; when the second thin film layer material is gallium arsenide, the thickness is 60~140nm. When the third thin film material is germanium, the thickness is 500~700nm; when the third thin film material is zinc sulfide, the thickness is 250~550nm. When the fourth thin film material is aluminum oxide, the thickness is 350~450nm; when the fourth thin film material is silicon monoxide, the thickness is 250~450nm.

3. The photothermal regulated multilayer thin film according to claim 1, characterized in that, The first thin film layer material is aluminum oxide; the second thin film layer material is silicon; the third thin film layer material is germanium; and the fourth thin film layer material is aluminum oxide.

4. A method for preparing a photothermally modulated multilayer thin film according to any one of claims 1 to 3, characterized in that, The preparation method includes: Using the constructive interference of the target structural color in the visible light band as the initial constraint, and combining the material's hardness and optical properties in the visible and mid-to-long infrared bands, the material and thickness range of the first thin film layer are screened and determined from the candidate materials. The material of the second thin film layer is selected and determined based on the optical properties of the first thin film layer material, so that the first thin film layer and the second thin film layer form a double-layer interference structure to jointly regulate the visible light structural color. Based on the optical properties of the first and second thin film layer materials in the mid- and long-infrared bands, and the Brewster angle requirement at the target angle, the third thin film layer material was screened and determined. Based on the optical properties of the first, second, and third thin film layer materials in the mid- and long-infrared bands, the fourth thin film layer material was screened and determined so that the four thin films could form a Fabry-Perot resonant cavity structure. An optical simulation model of a multilayer thin film was constructed, and the thickness of each thin film layer was determined by multiphysics simulation. Then, radio frequency magnetron sputtering was used to deposit each thin film layer sequentially on the surface of a graphite substrate to prepare the photothermal regulated multilayer thin film.

5. The preparation method according to claim 4, characterized in that, The optical properties include extinction coefficient and refractive index.

6. The preparation method according to claim 4, characterized in that, The thickness range of the first thin film layer is determined by the following formula: In the formula, d The thickness of the first thin film layer material. m It is a positive integer. λ For wavelength, n The refractive index of the first thin film layer material is . The target angle for directional radiation.

7. The preparation method according to claim 4, characterized in that, The radio frequency magnetron sputtering power is 70~120W, and the gas pressure is 0.5~1.0Pa; and / or The sputtering gas used in the radio frequency magnetron sputtering includes at least one of oxygen or argon.

8. The preparation method according to claim 7, characterized in that, The second thin film layer is prepared by radio frequency magnetron sputtering combined with a bias voltage; wherein the sputtering power is 70~90W, the gas pressure is 0.5~0.8Pa, and the bias voltage is -22~-18V; and / or The first thin film layer was deposited sequentially by radio frequency magnetron sputtering under both unbiased and biased conditions; wherein the sputtering power was 90~110W, the gas pressure was 0.5~0.8Pa, and the bias voltage was -85~-75V; the thickness of the film layer deposited under unbiased conditions was 15~20nm.

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