Photo-thermal double-control type infrared stealth metamaterial and preparation method thereof

Abstract

According to the photo-thermal double-control type infrared stealth metamaterial and the preparation method thereof provided by the invention, the photo-induced or thermally induced phase change of a VO2 material is realized by virtue of efficient and controllable light absorption and thermal conversion of a plasmon nanostructure aiming at the infrared stealth requirement under an active detection background, so that the light modulation of the infrared emissivity of the metamaterial is realized. The test results of infrared emissivity, in-situ Raman spectrum and the like of the material under different temperatures and light irradiation show that due to the introduction of metal nano island films such as Au, Ag, Al and the like, the emissivity mutation phenomenon after phase change of a traditional VO2 film is inhibited, and continuous controllable attenuation of the emissivity under temperature control or 532 nm or 980 nm and other laser irradiation is achieved. The photo-thermal double-control type infrared stealth metamaterial is based on the plasmon photo-thermal effect and the infrared radiation increment inhibition effect of thermally induced phase change, active laser marks can be effectively resisted, the problems that a traditional infrared stealth means is single and insufficient in regulation and control are solved, and a new design thought is provided for intelligent stealth equipment development.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and specifically relates to a photothermal dual-control infrared stealth metamaterial with high stability and linearly adjustable infrared emissivity with light intensity, and a preparation method thereof. Background Art

[0002] In the military, active target marking technology based on the laser-thermal coupling effect has become an important research direction in the reconnaissance field. The technical principle is to use a high-energy laser beam in a specific wavelength band to irradiate the surface of military equipment in a targeted manner. Through the interaction between the laser and the target material, such as metal alloys, ceramic-based composites, and polymer-absorbing coatings, the laser efficiently converts the light energy into heat energy. This energy conversion process not only triggers electron transitions on the surface of the material but also, through the Joule heat conduction mechanism, causes a rapid increase in the temperature of the target area, forming a region of thermal radiation with a significant temperature gradient.

[0003] This active target marking technology can break through the shielding threshold of traditional camouflage materials by enhancing the target's infrared radiation intensity in the atmospheric window, making the irradiated area appear as a high-contrast "hot spot" feature in the infrared imaging system. Combined with a multi-spectral collaborative detection system, this technology can build a cross-band feature recognition and marking chain, significantly improving the capture probability and strike accuracy of guided weapons on marked targets. It is worth noting that this non-contact marking method can be achieved without physical contact and has real-time tracking characteristics for battlefield targets, resulting in a significant reduction in the battlefield survivability of the marked target, posing new challenges to the concealment strategy of existing military targets.

[0004] The infrared emissivity of the thermotropic phase change material vanadium dioxide (VO2) can undergo a sudden change near 341K, so it has received widespread attention in military fields such as stealth equipment design, and a series of related products have been developed. Chinese patent application CN119956294A achieves thermal control of infrared emissivity while lowering the phase transition temperature of VO2 through a sandwich structure of two inorganic functional layers sandwiching a vanadium dioxide layer; Chinese patent application CN119798751A obtains modified vanadium dioxide by modifying vanadium dichloride with metal compounds, and stacks it vertically as an ink layer with a polymer protective layer, a metal layer, and a substrate layer, thereby reducing the infrared emissivity of the material and the phase transition temperature of the modified vanadium dioxide; Chinese patent CN113917755B achieves emissivity control and thermal management around the phase transition temperature of 341K through a composite design of a substrate, a metal layer, and multiple combined film layers; Chinese patent CN113534315B achieves control of infrared emissivity and radiative heat dissipation in the atmospheric absorption window band at 341K by embedding the phase change material VO2 into the metal layer.

[0005] The application of the above products in the field of military stealth still has the following problems: (1) The means of controlling the phase change of VO2 is currently basically limited to voltage or ambient temperature control. In the face of increasingly complex military detection technologies (such as laser detection), the control means of existing products are basically ineffective or cannot be turned on in time (the laser detection beam arrives instantly, and the external control device responds slowly); (2) The infrared emissivity of products containing VO2 shows a sudden change before and after the phase change temperature (below the phase change temperature, the infrared emissivity is high, above the phase change temperature or near it, the infrared emissivity remains low), and the phase change condition of 341K has a significant temperature difference barrier with most actual application scenarios (such as human stealth, electronic device stealth, etc.), forcing the system to rely on additional energy input to maintain the phase change triggering conditions, resulting in a significant reduction in energy efficiency; (3) The current literature and patent reports In stealth design, the VO2 functional layer is mostly based on lattice reconstruction methods such as metal element doping (such as CN119411084A, CN119798751A) or high-temperature annealing (such as CN112331555A). However, such methods generally have the defect of a narrow process control window, and require precise matching of key parameters such as doping concentration, annealing temperature and duration, resulting in a doubling of production process complexity and equipment precision requirements; in addition, the lattice reconstruction process involves multi-level energy input and interface reaction control, which not only greatly increases equipment and R&D costs, but is also more likely to cause problems such as decreased material phase purity and accumulation of grain boundary defects, resulting in a significant reduction in device batch stability and repeatability of optical performance. Summary of the Invention

[0006] In response to the problems existing in the above-mentioned prior art, the present invention provides a photothermal dual-control infrared stealth metamaterial, which realizes linear and continuous regulation of infrared emissivity under both temperature and light regulation, and exhibits different wavelength-dependent characteristics under different laser wavelengths.

[0007] The optical-thermal dual-control infrared stealth metamaterial provided by the present invention comprises, from bottom to top, a base layer, a plasmonic metal layer, and a vanadium dioxide functional layer; the plasmonic metal layer is a metal nano-island film, and the metal is any one of Au, Ag, and Al.

[0008] When the above-mentioned plasmon metal layer is an Au nano-island film with a thickness of 33nm to 37nm or 82nm to 90nm, dynamic linear and continuous regulation of the infrared emissivity can be achieved by heating it in the temperature range of 30°C to 100°C, or by correspondingly adjusting the laser irradiation power at an operating wavelength of 510nm to 540nm or 720nm to 1000nm.

[0009] When the above-mentioned plasmon metal layer is an Ag nano-island film with a thickness of 9nm to 11nm or 42nm to 49nm, dynamic linear and continuous regulation of the infrared emissivity can be achieved by heating it in the temperature range of 30°C to 100°C, or by adjusting the laser irradiation power at an operating wavelength of 480nm to 580nm or 790nm to 990nm.

[0010] When the above-mentioned plasmon metal layer is an Al nano-island film with a thickness of 24nm to 26nm or 51nm to 59nm, dynamic linear and continuous regulation of the infrared emissivity can be achieved by heating it in the temperature range of 30°C to 100°C, or by adjusting the laser irradiation power at an operating wavelength of 532nm to 650nm or 760nm to 1000nm.

[0011] The base layer material is any one of silicon, sapphire and silicon carbide, and the thickness of the base layer is 500 μm to 2000 μm.

[0012] 3. The optical-thermal dual-control infrared stealth metamaterial according to claim 1, wherein the vanadium dioxide functional layer is a VO2 thin film with a thickness of 150 nm to 300 nm.

[0013] The preparation method of the optical-thermal dual-control infrared stealth metamaterial of the present invention comprises the following steps:

[0014] Step 1: After cleaning and drying the base layer material, a plasmon metal layer is deposited on the surface of the base layer material using a DC magnetron sputtering process. The sputtering power is 65W to 80W, the argon flow rate is 45sccm to 70sccm, and the gas pressure is maintained at 0.1Pa to 0.8Pa. During sputtering, annealing is performed at 300℃ to 400℃.

[0015] Step 2: A vanadium dioxide functional layer is deposited on the surface of the plasmon metal layer in step 1 using a DC magnetron sputtering process. The sputtering power is 55W to 90W, the argon flow rate is 40sccm to 70sccm, and the gas pressure is maintained at 0.1Pa to 0.8Pa. The sputtering time is 2.1h to 2.8h. After deposition, the layer is annealed at 500℃ to 580℃ for 2.5h to 3h, and cooled to room temperature to obtain a photothermal dual-control infrared stealth metamaterial.

[0016] In the above step 1, when the plasmon metal layer is an Au nano-island film with a thickness of 33 nm to 37 nm or 82 nm to 90 nm, the sputtering time is 28 s to 32 s or 95 s to 100 s, respectively.

[0017] In the above step 1, when the plasmon metal layer is an Ag nano-island film with a thickness of 9 nm to 11 nm or 42 nm to 49 nm, the sputtering time is 18 s to 22 s or 48 s to 54 s, respectively.

[0018] In the above step 1, when the plasmon metal layer is an Al nano-island film with a thickness of 24 nm to 26 nm or 51 nm to 59 nm, the sputtering time is 47 s to 53 s or 93 s to 107 s, respectively.

[0019] The wavelength-dependent optical control of the infrared stealth metamaterial, a dual-controllable optical and thermal metamaterial, is achieved through the combined action of a plasmonic metal layer and a vanadium dioxide functional layer stacked on a substrate. By manipulating the metal type and thickness of the plasmonic metal layer (primarily determined by the sputtering duration and power), the intrinsic absorption of the infrared stealth metamaterial can be matched to the operating wavelengths of different lasers.

[0020] The photothermal dual-control infrared stealth metamaterial provided by the present invention has the following notable features: it realizes linear continuous dynamic regulation of photothermal dual-control infrared emissivity based on plasmonic metal nanostructures (metal nano-island films such as Au, Ag, and Al) and thermoinduced phase change material VO2. Furthermore, the present invention utilizes the efficient and controllable light absorption and heat conversion characteristics of plasmonic nanostructures to successfully induce and drive the VO2 material to undergo photoinduced phase change, thereby realizing optical modulation of the infrared emission behavior of the metasurface. On the other hand, the metamaterial structure makes full use of the inherent temperature sensitivity of the VO2 material. In the thermal control mode, when the structure is subjected to external overall heating or the ambient temperature changes, the infrared emissivity of the structure as a whole also shows a significant linear continuous downward trend as the temperature rises. Thermoinduced continuous dynamic infrared emissivity modulation based on the temperature field is realized.

[0021] The beneficial effects of the present invention are as follows:

[0022] 1. Effectively suppress emissivity mutation: The Au, Ag, and Al metal nano-island film structure introduced into the plasmonic metal layer significantly suppresses the infrared emissivity mutation phenomenon that occurs in traditional VO2 thin films during the phase change process. As the laser radiation power or heating temperature increases, the infrared emissivity shows a linear continuous decrease from high to low.

[0023] 2. Non-contact optical control: Remote, non-contact control of infrared emissivity can be achieved using an external laser detection beam. It is easy to operate and responds quickly, and can be applied to a variety of application scenarios based on the laser-thermal coupling effect.

[0024] 3. To cope with lasers of various detection wavelengths (wavelength-dependent characteristics): According to actual application requirements, intrinsic absorption is controlled by selecting different metal types and deposition thicknesses. For example, under the irradiation of lasers of specific wavelengths (such as 532nm, 800nm, 980nm), continuous and controllable attenuation of infrared emissivity can be achieved, providing flexible dynamic stealth capabilities.

[0025] 4. Highly Efficient Countermeasures Against Active Detection: The infrared radiation increment suppression mechanism, based on the plasmon photothermal effect, offers high photothermal efficiency. By varying the irradiation power of the detection laser beam, it can effectively counter active laser marking technology, significantly improving the target's infrared stealth performance.

[0026] 5. The preparation method is easy to operate and low-cost: the plasmonic metal layer has strong selectivity, the magnetron sputtering preparation method is widely used, the large-scale preparation cost is controllable, the preparation process is simple, and the equipment requirements are low. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The following are SEM images of various thin films deposited on the surface of Si wafers in Comparative Example 1 and Examples 1, 3, and 5. Among them, (a) is Si + VO2; (b) is Si + Au; (c) is Si + Al; (d) is Si + Ag; (e) is Si + Ag + VO2; (f) is Si + Au + VO2; and (g) is Si + Al + VO2.

[0028] Figure 2 It is the normalized absorption spectrum of the light-thermal dual-control infrared stealth metamaterial in Examples 1, 3, 5, and 6.

[0029] Figure 3 Graph showing the relationship between the emissivity of the optical-thermal dual-control infrared stealth metamaterial in Examples 1 and 2 under narrowband visible light and broadband visible light absorption and temperature.

[0030] Figure 4 Graph showing the relationship between the emissivity of the optical-thermal dual-control infrared stealth metamaterial in Examples 3 and 4 under narrowband visible light and broadband visible light absorption and temperature.

[0031] Figure 5 Graph showing the relationship between the emissivity of the optical-thermal dual-control infrared stealth metamaterial in Examples 5 and 6 under narrowband visible light and broadband visible absorption and temperature.

[0032] Figure 6 Graph showing the relationship between the emissivity of the optical-thermal dual-control infrared stealth metamaterial in Examples 1, 3, and 5 under narrowband visible light and broadband visible absorption and temperature.

[0033] Figure 7 This is a graph showing the relationship between the emissivity of the thermotropic phase change VO2 material in Example 1 and the photothermal dual-control infrared stealth metamaterial in Example 5 and the change in irradiation light intensity under laser irradiation with an operating wavelength of 532 nm.

[0034] Figure 8 This is a relationship diagram of the emissivity of the optical-thermal dual-control infrared stealth metamaterial in Examples 1, 3, and 5 as a function of irradiation power under laser irradiation at an operating wavelength of 532 nm.

[0035] Figure 9 1 is a graph showing the relationship between the emissivity of the optical-thermal dual-control infrared stealth metamaterial in Example 5 and the irradiation power under laser irradiation at working wavelengths of 532 nm and 980 nm, respectively.

[0036] Figure 10 This is the effect of the temperature of the thermally induced phase change VO2 material on the Raman spectrum in Example 1.

[0037] Figure 11 This is the effect of irradiation power on the Raman spectrum of the thermally induced phase change VO2 material in Example 1 under laser irradiation with an operating wavelength of 532nm.

[0038] Figure 12 This is the effect of temperature on the Raman spectrum of the optical-thermal dual-control infrared stealth metamaterial in Example 5.

[0039] Figure 13 This is the effect of irradiation power on the Raman spectrum of the optical-thermal dual-control infrared stealth metamaterial in Example 5 under laser irradiation with an operating wavelength of 532 nm. DETAILED DESCRIPTION

[0040] The present invention provides a photothermal dual-control infrared stealth metamaterial, which adopts a multi-layer composite structure, which consists of a base layer, a plasmon metal layer and a vanadium dioxide functional layer from bottom to top, wherein the plasmon metal layer achieves wavelength selective regulation through a metal nano-island film structure. Specifically, a layer of metal nano-island film is deposited on the surface of the base layer material by magnetron sputtering as a plasmon metal layer, and the metal type and thickness are adjusted to match the target laser wavelength. Subsequently, a VO2 thin film is deposited on its surface by magnetron sputtering. When irradiated by laser, the plasmon metal layer efficiently converts the incident light energy in the 532nm or 980nm band into heat energy through the localized surface plasmon resonance effect, triggering the semiconductor phase-metal phase transformation of the VO2 material. Experiments have confirmed that when the laser power density gradually increases linearly, the infrared emissivity of the photothermal dual-control infrared stealth metamaterial exhibits a linear attenuation characteristic in the 8-14μm band and has continuous adjustability dependent on the optical power. Compared to the sudden infrared emissivity response of traditional VO2 phase-change materials, the introduction of metal nano-island films in this metamaterial reduces the phase-change activation threshold by approximately 40%. The non-uniform thermal field distribution effectively suppresses the sudden emissivity change during the phase-change process. This photothermal synergistic control mechanism enables dynamic camouflage of a target's infrared signature by simply varying the incident laser power at a fixed ambient temperature. This is particularly useful for countering target recognition technologies based on laser active marking.

[0041] The principles of each layer in the structure of the optical-thermal dual-control infrared stealth metamaterial of the present invention are described as follows:

[0042] The base layer is used to provide physical support for other structural layers and absorb the energy transmitted by the plasmon metal layer and the vanadium dioxide functional layer. It can be made of high infrared reflective materials such as silicon (Si), sapphire (Al2O3), and silicon carbide (SiC). Since the base layer is used to reflect infrared radiation, its thickness is generally much higher than the radiation wavelength. The thickness of the base layer is 500μm to 2000μm.

[0043] The plasmonic metal layer is composed of a metal nano-island film, the material of which is selected from any one of Au, Ag, and Al. The target laser wavelength is matched by adjusting the type of metal and the thickness of the island film. Specifically, when the plasmonic metal layer is an Au nano-island film with a thickness of 33nm to 37nm or 82nm to 90nm, heating it within a temperature range of 30°C to 100°C, or correspondingly adjusting the laser irradiation power at an operating wavelength of 510nm to 540nm or 720nm to 1000nm, dynamic linear continuous regulation of infrared emissivity can be achieved; when the plasmonic metal layer is an Ag nano-island film with a thickness of 9nm to 11nm or 42nm to 49nm, heating it within a temperature range of 30°C to 100°C, or correspondingly adjusting the laser irradiation power at an operating wavelength of 510nm to 540nm or 720nm to 1000nm, dynamic linear continuous regulation of infrared emissivity can be achieved. By adjusting the laser irradiation power at the working wavelength of 480nm to 580nm or 790nm to 990nm, dynamic linear and continuous regulation of infrared emissivity can be achieved. When the plasmon metal layer is an Al nano-island film with a thickness of 24nm to 26nm or 51nm to 59nm, heating it within a temperature range of 30℃ to 100℃, or adjusting the laser irradiation power at the working wavelength of 532nm to 650nm or 760nm to 1000nm, dynamic linear and continuous regulation of infrared emissivity can be achieved. By changing the type of metal, its localized surface plasmon resonance peak can be adjusted to have intrinsic absorption characteristics in the narrow-band visible light or broadband near-infrared spectral range. At the same time, for every 10nm increase in the thickness of the metal nano-island film, its resonance absorption peak position can produce a red shift of 10nm to 50nm. By combining different metal materials and thickness parameters, precise matching of the laser wavelength and the plasmon absorption peak can be achieved, thereby forming a gradient photothermal conversion efficiency within the infrared stealth band. Experimental verification has shown that by optimizing the selection and thickness of metal materials, the resonant absorption peak of the plasmonic metal layer can be dynamically adapted to the operating wavelengths of different laser detection systems. The resulting wavelength-selective heating effect can achieve gradient regulation of infrared radiation for specific laser bands, thereby effectively enhancing the ability to counter multi-spectral laser active marking technology.

[0044] The vanadium dioxide functional layer realizes dynamic regulation of infrared emissivity in the form of continuous phase change. The thickness of the VO2 film is preferably 150nm to 300nm, and it is directly deposited on the surface of the plasmonic metal layer. Through the photothermal conversion effect of the plasmonic metal layer, the vanadium dioxide functional layer can trigger a reversible phase change between the semiconductor state (low temperature) and the metallic state (high temperature) under laser irradiation. When VO2 is in a mixed phase change state, it exhibits a continuous gradual change in emissivity in the 8-14μm long-wave infrared band, and the phase change response time is shortened to the millisecond level. In particular, the VO2 film forms a spatially non-uniform heat conduction path by coupling with the structure of the discontinuous metal nano-island film, effectively suppressing the emissivity step mutation caused by the global synchronous phase change of the traditional VO2 film, greatly improving the modulation depth of the infrared radiation intensity compared to the traditional structure, while ensuring that a stable baseline infrared feature is maintained without an external heat source, realizing adaptive infrared stealth and dynamic camouflage functions in complex environments.

[0045] In order to make the purpose, technical solutions and advantages of the present invention more clear, the technical solutions of the present invention are described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other in any manner. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited by the following specific embodiments.

[0046] Comparative Example 1

[0047] The Si wafer was immersed in pure water, assisted by 1MHz megasonic ultrasound for 10 minutes, and then rinsed with alcohol on its surface for 3 minutes. After being purged and dried with nitrogen, the Si wafer was fixed on the sample stage in the cavity of the dual-target frequency magnetron sputtering device. A VO2 target material with a purity of 99.99% was used to deposit a VO2 film with a thickness of 200nm on the surface of the Si wafer as a thermally induced phase change layer using a DC magnetron sputtering process. The sputtering power was 70W, the argon flow rate was 50sccm and the gas pressure was maintained at 0.7Pa. The sputtering time was 2.5h. After sputtering, it was annealed at 550℃ for 3h. After cooling to room temperature, a thermally induced phase change VO2 material was obtained.

[0048] Example 1

[0049] Step 1: Immerse the Si wafer in pure water, supplemented with 1MHz megasonic ultrasound for 10 minutes, then rinse its surface with alcohol for 3 minutes, blow dry with nitrogen, and fix the Si wafer on the sample stage in the cavity of the dual-target frequency magnetron sputtering device. Use an Al target material with a purity of 99.99% to deposit a 25nm thick Al nano-island film as a plasmon metal layer on the surface of the Si wafer using a DC magnetron sputtering process. The sputtering power is 70W, the argon flow rate is 50sccm and the gas pressure is maintained at 0.7Pa. The sputtering time is 50s, and annealing is performed at 380°C while sputtering.

[0050] Step 2: A VO2 thin film with a thickness of 200±5 nm is deposited on the surface of the Al nano-island film in step 1 by DC magnetron sputtering as a vanadium dioxide functional layer. The DC magnetron sputtering power is 70 W, the argon flow rate is 50 sccm and the gas pressure is maintained at 0.7 Pa. The sputtering time is 2.5 h. After sputtering, annealing is performed at 550°C for 3 h and cooled to room temperature to form an Al nano-island film and a VO2 composite thin film on the Si wafer, thereby obtaining a photothermal dual-control infrared stealth metamaterial.

[0051] Example 2

[0052] Step 1: Immerse the Si wafer in pure water, supplemented with 1MHz megasonic ultrasound for 10 minutes, then rinse its surface with alcohol for 3 minutes, blow dry with nitrogen, and fix the Si wafer on the sample stage in the cavity of the dual-target frequency magnetron sputtering device. Use an Al target material with a purity of 99.99% to deposit a 55nm thick Al nano-island film as a plasmon metal layer on the surface of the Si wafer using a DC magnetron sputtering process. The sputtering power is 70W, the argon flow rate is 50sccm and the gas pressure is maintained at 0.7Pa. The sputtering time is 100s, and annealing is performed at 380°C while sputtering.

[0053] Step 2: A VO2 thin film with a thickness of 200±5 nm is deposited on the surface of the Al nano-island film in step 1 by DC magnetron sputtering as a vanadium dioxide functional layer. The DC magnetron sputtering power is 70 W, the argon flow rate is 50 sccm and the gas pressure is maintained at 0.7 Pa. The sputtering time is 2.5 h. After sputtering, annealing is performed at 550°C for 3 h and cooled to room temperature to form an Al nano-island film and a VO2 composite thin film on the Si wafer, thereby obtaining a photothermal dual-control infrared stealth metamaterial.

[0054] Example 3

[0055] Step 1: Immerse the Si wafer in pure water, supplemented with 1MHz megasonic ultrasound for 10 minutes, then rinse its surface with alcohol for 3 minutes, blow dry with nitrogen, and fix the Si wafer on the sample stage in the cavity of the dual-target frequency magnetron sputtering device. Use a 99.99% pure Ag target material to deposit a 10nm thick Ag nano-island film as a plasmon metal layer on the surface of the Si wafer using a DC magnetron sputtering process. The sputtering power is 70W, the argon flow rate is 50sccm and the gas pressure is maintained at 0.7Pa. The sputtering time is 20s, and annealing is performed at 380°C while sputtering.

[0056] Step 2: A VO2 thin film with a thickness of 200±5nm is deposited on the surface of the Ag nano-island film in step 1 by DC magnetron sputtering as a vanadium dioxide functional layer. The DC magnetron sputtering power is 70W, the argon flow rate is 50sccm and the gas pressure is maintained at 0.7Pa. The sputtering time is 2.5h. After sputtering, annealing is performed at 550℃ for 3h and cooled to room temperature to form an Ag nano-island film and a VO2 composite thin film on the Si wafer, thereby obtaining a photothermal dual-control infrared stealth metamaterial.

[0057] Example 4

[0058] Step 1: Immerse the Si wafer in pure water, supplemented with 1MHz megasonic ultrasound for 10 minutes, then rinse its surface with alcohol for 3 minutes, blow dry with nitrogen, and fix the Si wafer on the sample stage in the cavity of the dual-target frequency magnetron sputtering device. Use a 99.99% pure Ag target material to deposit a 45nm thick Ag nano-island film as a plasmon metal layer on the surface of the Si wafer using a DC magnetron sputtering process. The sputtering power is 70W, the argon flow rate is 50sccm and the gas pressure is maintained at 0.7Pa. The sputtering time is 52s, and annealing is performed at 350°C while sputtering.

[0059] Step 2: A VO2 thin film with a thickness of 200±5nm is deposited on the surface of the Ag nano-island film in step 1 by DC magnetron sputtering as a vanadium dioxide functional layer. The DC magnetron sputtering power is 70W, the argon flow rate is 50sccm and the gas pressure is maintained at 0.7Pa. The sputtering time is 2.5h. After sputtering, annealing is performed at 550℃ for 3h and cooled to room temperature to form an Ag nano-island film and a VO2 composite thin film on the Si wafer, thereby obtaining a photothermal dual-control infrared stealth metamaterial.

[0060] Example 5

[0061] Step 1: Immerse the Si wafer in pure water, supplemented with 1MHz megasonic ultrasound for 10 minutes, then rinse its surface with alcohol for 3 minutes, blow dry with nitrogen, and fix the Si wafer on the sample stage in the cavity of the dual-target frequency magnetron sputtering device. Use a 99.99% pure Au target material to deposit a 35nm thick Au nano-island film as a plasmon metal layer on the surface of the Si wafer using a DC magnetron sputtering process. The sputtering power is 70W, the argon flow rate is 50sccm and the gas pressure is maintained at 0.7Pa. The sputtering time is 30s, and annealing is performed at 300°C while sputtering.

[0062] Step 2: A VO2 thin film with a thickness of 200±5 nm is deposited on the surface of the Au nano-island film in step 1 by DC magnetron sputtering as a vanadium dioxide functional layer. The DC magnetron sputtering power is 70 W, the argon flow rate is 50 sccm and the gas pressure is maintained at 0.7 Pa. The sputtering time is 2.5 h. After sputtering, annealing is performed at 550°C for 3 h and cooled to room temperature to form an Au nano-island film and a VO2 composite thin film on the Si wafer, thereby obtaining a photothermal dual-control infrared stealth metamaterial.

[0063] Example 6

[0064] Step 1: Immerse the Si wafer in pure water, supplemented with 1MHz megasonic ultrasound for 10 minutes, then rinse its surface with alcohol for 3 minutes, blow dry with nitrogen, and fix the Si wafer on the sample stage in the cavity of the dual-target frequency magnetron sputtering device. Use a 99.99% pure Au target material to deposit an 85nm thick Au nano-island film as a plasmon metal layer on the surface of the Si wafer using a DC magnetron sputtering process. The sputtering power is 70W, the argon flow rate is 50sccm and the gas pressure is maintained at 0.7Pa. The sputtering time is 96s, and annealing is performed at 300°C while sputtering.

[0065] Step 2: A VO2 thin film with a thickness of 200±5 nm is deposited on the surface of the Au nano-island film in step 1 by DC magnetron sputtering as a vanadium dioxide functional layer. The DC magnetron sputtering power is 70 W, the argon flow rate is 50 sccm and the gas pressure is maintained at 0.7 Pa. The sputtering time is 2.5 h. After sputtering, annealing is performed at 550°C for 3 h and cooled to room temperature to form an Au nano-island film and a VO2 composite thin film on the Si wafer, thereby obtaining a photothermal dual-control infrared stealth metamaterial.

[0066] The various thin films deposited on the surface of the Si wafer in the comparative example 1 and embodiments 1, 3, and 5 were characterized by SEM. Figure 1 .Depend on Figure 1It can be seen that in Comparative Example 1, the VO2 thin film is directly deposited on the Si wafer by magnetron sputtering, and its texture is relatively uniform, which ensures the temperature uniformity per unit area of ​​the sample during heating and laser irradiation in infrared thermal imaging; in Examples 1, 3, and 5, the Al thin film, Ag thin film, and Au thin film first deposited on the Si wafer by magnetron sputtering present a relatively uniform island structure, that is, a layer of metal nano-island film is first deposited on the Si wafer; further, a layer of VO2 thin film is deposited on the metal nano-island film by magnetron sputtering. Compared with the metal nano-island film without VO2 thin film, the roughness of the metal nano-island film and VO2 composite film formed on the Si wafer is slightly increased, but the grains are tightly bonded, there are no obvious visible cracks or accumulation defects, and the overall texture is uniform and dense.

[0067] In order to illustrate the influence of the intrinsic properties of the material on the surface plasmon resonance characteristics of the composite film when different metal nano-island films are introduced into the VO2 film, as well as the dependence on different excitation wavelengths, the present invention achieves effective regulation of the surface plasmon absorption peak of the sample by optimizing the thickness of the metal nano-island film and the annealing temperature and other parameters. Specifically, when the sputtering time of the Al, Ag, and Au targets described in step 1 of the above-mentioned Examples 1, 3, and 5 is 50s, 20s, and 30s respectively, the intrinsic absorption of the composite film sample obtained in step 2 is regulated to the narrowband visible light region; when the sputtering time of the Al, Ag, and Au targets described in the above-mentioned Examples 2, 4, and 6 is 100s, 52s, and 96s respectively, the intrinsic absorption of the composite film sample obtained in step 2 is regulated to the broadband near-infrared light region. Combined with the currently widely used laser types, the composite film samples of Examples 1, 3, 5, and 6 were finally selected, which have narrow-band absorption in the visible light band and broadband absorption in the near-infrared band. The normalized absorption spectra are as follows: Figure 2 As shown in the figure, the absorption peaks of the composite film samples of Examples 1, 3, and 5 are all located near 532 nm. The absorption differences at 532 nm between the composite film samples of Examples 3 and 5 are relatively small, while the absorption peak of the composite film sample of Example 1 is slightly red-shifted. Furthermore, the broadband absorption composite film sample of Example 6 exhibits high absorption efficiency at 980 nm, laying the foundation for subsequent studies of photothermal effects under 532 nm and 980 nm irradiation.

[0068] In order to illustrate the effect of the type of metal nano-island film on the infrared emissivity of VO2 thin films, the emissivity variation with temperature of the composite film samples with narrow-band absorption characteristics described in Examples 1, 3, and 5 and the composite film samples with broadband absorption characteristics described in Examples 2, 4, and 6 were studied respectively. Figures 3 to 6 As shown. Figures 3-5It can be seen that the infrared emissivity of the composite film samples of Examples 1 to 6 shows a trend of gradually decreasing with increasing temperature during the heating process of 30°C to 100°C. Specifically, the infrared emissivity value of the composite film sample of Example 1 linearly and continuously decays from 0.83 to 0.41, and the emissivity adjustment range is 0.42; the infrared emissivity of the composite film sample of Example 2 linearly and continuously decays from 0.80 to 0.42, and the emissivity adjustment range is 0.38; the infrared emissivity of the composite film sample of Example 3 linearly and continuously decays from 0.68 to 0.38, and the emissivity adjustment range is 0.30; the infrared emissivity of the composite film sample of Example 4 linearly and continuously decays from 0.70 to 0.36, and the emissivity adjustment range is 0.34; the infrared emissivity of the composite film sample of Example 5 linearly and continuously decays from 0.69 to 0.32, and the emissivity adjustment range is 0.37; the infrared emissivity of the composite film sample of Example 6 linearly and continuously decays from 0.69 to 0.31, and the emissivity adjustment range is 0.38. The infrared emissivity of the composite film samples of Examples 1 to 6 shows similar trends in temperature variation. That is, the infrared emissivity of the composite film samples of Examples 1 to 6 is less affected by the thickness of the introduced metal nano-island film (i.e., different absorption characteristics). However, it is worth noting that there are differences in the emissivity values ​​corresponding to specific temperature points among the three groups of composite film samples of Examples 1 to 2, Examples 3 to 4, and Examples 5 to 6. Furthermore, Figure 6 The comparison curves of the emissivity of the composite film samples described in Examples 1, 3, and 5 as a function of temperature are shown. At the same temperature, the emissivity of the optical-thermal dual-control infrared stealth metamaterial is ranked as Example 1 > Example 3 > Example 5.

[0069] Next, the following two issues are explained: one is the effect of the introduction of metal nano-island films and the type of metal nano-island films on the surface plasmon resonance characteristics and photothermal effects of the composite film; the other is to explore the changes in infrared emissivity of the composite film samples described in Example 5, which exhibits narrow-band absorption of visible light, and Example 6, which exhibits broadband absorption of near-infrared light, under 532nm and 980nm laser irradiation, and further reveal the wavelength-dependent characteristics of the light-induced composite film emissivity regulation, such as Figures 7-9 First, Si was selected as the substrate material, and the thermotropic phase change VO2 material in Comparative Example 1 without Au nano-island film was set as the control group to deeply analyze the dynamic relationship between infrared emissivity and radiation power. Figure 7As shown, under light irradiation of the same intensity, the infrared emissivity of the VO2 film in which the Au nano-island film is not introduced in Comparative Example 1 is higher than that of the composite film sample of Example 5 containing the Au nano-island film. In other words, the introduction of the Au nano-island film makes the infrared emissivity of the VO2 composite film (Example 5) significantly lower than that of the pure VO2 film under the same laser irradiation power, even at high irradiation power. This discovery strongly proves that the introduction of plasmon metal can effectively reduce the irradiation light intensity required for the VO2 film to reach the emissivity threshold. This is because the irradiation of resonant light effectively excites the surface plasmon resonance effect of the metal nano-island film in the composite film, thereby significantly improving the light absorption and heat conversion of the structure, making the temperature rise of the composite film more significant. Therefore, the change in the intensity of the irradiated light can be used to regulate the sample temperature, thereby achieving the control of the infrared emissivity, laying the foundation for the light-controlled manipulation of the infrared stealth function of the composite film.

[0070] Next, the infrared emissivity of the VO2 composite film introduced with three different metal (Al, Ag, Au) nano-island films in Examples 1, 3, and 5 is described as a function of the irradiation power under 532nm laser irradiation. Figure 8 As shown, under the same radiation power, the infrared emissivity of each sample is different. Specifically, the emissivity of the Al nano-island film and VO2 composite film in Example 1 is the highest. When the corresponding irradiation power changes from 58mW to 296mW, the emissivity still decays linearly and continuously from 0.83 to 0.41, and the emissivity regulation range is 0.42. Next is the emissivity of the Au nano-island film and VO2 composite film in Example 5, and the Ag nano-island film and VO2 composite film in Example 3. When the corresponding irradiation power of the composite film sample in Example 5 changes from 65mW to 298mW, the emissivity still decays linearly and continuously from 0.69 to 0.32, and the emissivity regulation range is 0.37; when the corresponding irradiation power of the composite film sample in Example 3 changes from 34mW to 275mW, the emissivity still decays linearly and continuously from 0.68 to 0.38, and the emissivity regulation range is 0.30. This result is consistent with Figure 6 The emissivity variation trend with temperature is quite consistent. The reason why the infrared emissivity variation curve with radiation power and the emissivity variation curve with temperature of the composite film samples of Example 5 and Example 3 are different may be that Figure 2 The above findings further demonstrate that the introduction of metal nano-island films produces plasmon resonance and photothermal effects in the VO2 composite films (Examples 1-6). Furthermore, differences in the intrinsic properties of the introduced metal nano-island film materials and the regulation of their plasmon absorption peaks lead to slight differences in the plasmon resonance and photothermal effects of the samples.

[0071] Further, for the sample of Example 5 with an absorption center wavelength of 532 nm, the changes in its infrared emissivity under laser irradiation of two wavelengths, 532 nm and 980 nm, were detected. Figure 9 As shown. The results show that the 980nm laser irradiation intensity required to achieve the same emissivity of the sample is significantly higher than the 532nm laser intensity. This indicates that the sample's absorption and thermal conversion efficiency for 532nm light is much higher than that for 980nm light, proving that the introduction of plasmonic metal nano-island film brings about the wavelength-dependent characteristics of light-induced infrared emissivity regulation of the composite film. It should be noted that the variation range of the laser irradiation power in the above experiments corresponds to the temperature variation range during the above heating (30℃~100℃).

[0072] Raman spectroscopy was used to characterize the phase transition behavior of the composite film formed on the substrate material in Example 5 above under different temperatures and laser irradiation, thereby verifying the corresponding relationship between the change in its emissivity and the crystal phase transition of the VO2 film, and further verifying the effectiveness of the light-induced phase transition and emissivity attenuation of the composite film. Raman spectroscopy testing was performed on a confocal Raman system (Jobin-Yvon) and a microscopic imaging system equipped with a piezoelectric shift stage. In-situ variable temperature Raman spectroscopy and surface plasmon treatment of the composite film in high and low temperature environments and real-time spectral detection were completed using a high and low temperature catalytic stage and a confocal Raman system. A continuous laser with a wavelength of 532nm was used as the excitation source for Raman scattering spectrum collection, and the laser was focused using a 50× objective lens. The Raman spectroscopy results of the VO2 film can provide an in-depth understanding of the structural evolution of the material during the metal-insulator phase transition (MIT) and monitor the phase transition process in real time. This phase transition usually occurs around 68°C and is characterized by a sudden change in the resistivity and optical properties of VO2. When the temperature reaches the MIT temperature range, the Raman peak positions and intensities change significantly: at room temperature, VO2 is in a monoclinic insulating phase, and its Raman spectrum displays several characteristic peaks corresponding to lattice vibration modes. As the temperature rises to the phase transition point, VO2 gradually transforms into a tetragonal rutile metallic phase, at which point the characteristic Raman peaks of the insulating phase weaken or even disappear. Figure 10 The Raman spectrum evolution of the sample of Comparative Example 1 at different temperature points during the heating process from room temperature to 70°C is shown. It is known that the insulating-metallic phase transition of VO2 polycrystalline thin film is a percolation process, which includes three stages: the nucleation of metal phase islands in the initial insulating film, the expansion of metal phase islands as the insulating phase shrinks, and the final complete conversion of the insulating phase to a metallic state. -1 There is no significant Raman signal except for the extremely weak characteristic peak. Although the insulating phase Raman peak has not shifted, its intensity continues to weaken with temperature rise. When the temperature is 70℃, most of the VO2 grains in the sample have transformed into a metallic state, and no new characteristic peaks are detected in the Raman spectrum. Subsequently, we changed the power of the 532nm laser and detected its effect on the Raman spectrum of the sample. Figure 11It can be seen that as the 532nm laser power gradually increases from 0.2mW, the -1 and 615cm -1 The characteristic peak intensity of the insulating phase gradually weakened. When the irradiation power reached 10mW, the characteristic peak intensity of the insulating phase almost disappeared. This result strongly proves that the VO2 thin film sample described in Comparative Example 1 has completely transformed from an insulating phase to a metallic phase. However, after the Au nano-island film was introduced in Example 5, the emissivity of the VO2 composite film decreased with the temperature gradient slope, that is, the emissivity showed a slow downward trend with increasing temperature and the mutation characteristic disappeared. Figure 12 As shown in the figure, during the heating process from room temperature to 70°C, the intensity of the insulating phase Raman characteristic peak of the sample described in Example 5 gradually weakened until it completely disappeared. This change trend is consistent with Figure 10 The results of the temperature-varying Raman spectrum of the sample in comparative example 1 are consistent. Further, a variable power irradiation experiment was carried out on the sample described in Example 5 using a 532nm laser. The results are as follows: Figure 13 As shown in Figure 2, the characteristic peak intensity of VO2 in the insulating phase continues to decay as the laser power gradually increases from 0.2mW to 10mW. When the laser power reaches 5mW, the characteristic peak intensity of the insulating phase has almost completely disappeared, indicating that VO2 has completely transformed into the metallic phase. Compared with the VO2 film without the introduction of Au nano-island film in Comparative Example 1 ( Figure 11 ), under the same laser power of 5 mW, the characteristic peaks of the insulating phase in the sample described in Example 5 almost completely disappear, strongly confirming that the introduction of the metal nanoisland film can reduce the laser power required for phase transition in the VO2 composite film. These two types of Raman spectroscopy test results strongly confirm that under specific light excitation conditions, the VO2 composite film exhibits significant surface plasmon resonance and the accompanying strong coupling characteristics of the photothermal conversion process. This conclusion is of great significance for improving the dynamic light control of infrared stealth layers.

Claims

1. A dual-control optical and thermal infrared stealth metamaterial, characterized by: The materials are, from bottom to top, a base layer, a plasmonic metal layer, and a vanadium dioxide functional layer; the plasmonic metal layer is a metal nano-island film, and the metal is any one of Au, Ag, and Al; When the plasmon metal layer is an Au nano-island film with a thickness of 33nm to 37nm or 82nm to 90nm, dynamic linear and continuous regulation of infrared emissivity can be achieved by heating within a temperature range of 30°C to 100°C, or by regulating the laser irradiation power at an operating wavelength of 510nm to 540nm or 720nm to 1000nm. When the plasmon metal layer is a Ag nano-island film with a thickness of 9nm to 11nm or 42nm to 49nm, dynamic linear and continuous regulation of infrared emissivity can be achieved by heating within a temperature range of 30°C to 100°C, or by regulating the laser irradiation power at an operating wavelength of 480nm to 580nm or 790nm to 990nm. When the plasmon metal layer is an Al nano-island film with a thickness of 24nm to 26nm or 51nm to 59nm, dynamic linear and continuous regulation of the infrared emissivity can be achieved by heating it in the temperature range of 30°C to 100°C, or by correspondingly regulating the laser irradiation power at an operating wavelength of 532nm to 650nm or 760nm to 1000nm.

2. The optical-thermal dual-control infrared stealth metamaterial according to claim 1, characterized in that: The base layer material is any one of silicon, sapphire and silicon carbide, and the thickness of the base layer is 500 μm to 2000 μm.

3. The optical-thermal dual-control infrared stealth metamaterial according to claim 1, characterized in that: The vanadium dioxide functional layer is a VO2 thin film with a thickness of 150nm to 300nm.

4. A method for preparing the optical-thermal dual-control infrared stealth metamaterial according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: Step 1: After cleaning and drying the base layer material, a plasmon metal layer is deposited on the surface of the base layer material using a DC magnetron sputtering process. The sputtering power is 65W to 80W, the argon flow rate is 45sccm to 70sccm, and the gas pressure is maintained at 0.1Pa to 0.8Pa. During sputtering, annealing treatment is performed at 300°C to 400°C. Step 2: A vanadium dioxide functional layer is deposited on the surface of the plasmon metal layer in step 1 using a DC magnetron sputtering process. The sputtering power is 55W to 90W, the argon flow rate is 40sccm to 70sccm, and the gas pressure is maintained at 0.1Pa to 0.8Pa. The sputtering time is 2.1h to 2.8h. After deposition, the layer is annealed at 500℃ to 580℃ for 2.5h to 3h, and cooled to room temperature to obtain a photothermal dual-control infrared stealth metamaterial.

5. The method for preparing the optical-thermal dual-control infrared stealth metamaterial according to claim 4, characterized in that: In step 1, when the plasmon metal layer is an Au nano-island film with a thickness of 33 nm to 37 nm or 82 nm to 90 nm, the sputtering time is 28 s to 32 s or 95 s to 100 s, respectively.

6. The method for preparing the optical-thermal dual-control infrared stealth metamaterial according to claim 4, characterized in that: In step 1, when the plasmon metal layer is an Ag nano-island film with a thickness of 9 nm to 11 nm or 42 nm to 49 nm, the sputtering time is 18 s to 22 s or 48 s to 54 s, respectively.

7. The method for preparing the optical-thermal dual-control infrared stealth metamaterial according to claim 4, characterized in that: In step 1, when the plasmon metal layer is an Al nano-island film with a thickness of 24 nm to 26 nm or 51 nm to 59 nm, the sputtering time is 47 s to 53 s or 93 s to 107 s, respectively.

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