An ultrathin absorber with infrared high absorption and a preparation method thereof

Abstract

The application discloses an ultrathin absorber with high infrared absorption and a preparation method thereof, which comprises a metal substrate layer, a metamaterial medium layer and a composite metal layer from bottom to top; the metal substrate layer is an infrared high-reflection metal with a thickness greater than 100 nm; the metamaterial medium layer is a semiconductor embedded vertical metal nanowire array with a thickness of 40-300 nm; and the composite metal layer is a bismuth-based composite metal with a thickness of 10-80 nm. The preparation method is simple and efficient, and the obtained ultrathin absorber has high infrared absorption characteristics.

Description

Technical Field

[0001] This invention belongs to the field of optical thin films (nanomaterials), specifically relating to an ultrathin absorber with high infrared absorption and its preparation method. Background Technology

[0002] In numerous fields such as aerospace, national defense, industrial monitoring, and fire early warning, the increasing demands for accuracy and sensitivity in monitoring components like infrared sensors and cameras have led to miniaturization and high integration of key devices. Thinning of the infrared absorber, the core working layer for capturing infrared light, is therefore crucial. Currently, the development of infrared absorbers is moving towards ultra-thin designs without sacrificing their absorption capacity.

[0003] Typically, simply reducing the thickness of the absorption layer will decrease the infrared extinction capability of the absorber. Therefore, many absorbers currently employ the Fabry-Perot (FP) cavity design concept, specifically utilizing a metal / dielectric / metal stacked structure to construct the optical cavity, achieving optical resonance confinement in the dielectric cavity and optical absorption in the metal layer. However, the achievement of optical resonance excitation at a specific wavelength λ in traditional FP resonant cavities mainly depends on the control of the dielectric layer thickness d (i.e., d≈λ / 4n, where n is the refractive index of the dielectric layer). Chinese patent CN206976376U discloses an infrared absorber based on a titanium nitride nanofilm / silicon dielectric layer / high conductivity metal reflective layer structure. Utilizing the FP cavity design, absorption in the 3.5μm band is achieved with a silicon dielectric cavity thickness of 250nm. Based on this calculation, to achieve absorption at the longer infrared wavelength of 11μm, a silicon dielectric layer of nearly 800nm ​​is required. Clearly, current absorbers constructed using conventional materials have large cavity modes, significantly hindering the ultrathinning of absorbers and making it difficult to meet the miniaturization requirements of integrated optical devices. Meanwhile, the absorption band adjustment of the FP cavity is strongly dependent on the cavity layer thickness, which exacerbates the mutual exclusion between thickness reduction and frequency band control.

[0004] Currently, to address the challenge of balancing ultrathinness and high absorption, many asymmetric photonic cavities (FP) based on metasurface structures are being developed. These cavities replace the original top metal layer with a metasurface layer containing a metal or dielectric microstructure. The phase shift introduced by the metasurface structure compensates for the insufficient phase transmission of the dielectric layer, enabling the excitation of the entire FP cavity resonance. Alternatively, the metasurface itself can excite plasmon resonance in a nanocavity, thereby reducing the dielectric layer thickness and achieving perfect absorption of multi-band infrared light. Furthermore, the absorption band can be tuned by varying the complex metal microstructure units and their arrangement within the metasurface, offering high design freedom. Chinese patent application CN113759449A discloses a frequency-tunable infrared absorber, specifically a metal cross-shaped unit array / dielectric layer / substrate structure, which absorbs at 11 μm. The total thickness, excluding the substrate, is approximately 500 nm, significantly thinner than traditional FP cavity structures, but the overall thickness remains relatively large. Furthermore, such absorbers require multiple processes such as thin film deposition and photolithography, resulting in complex processes, high costs for large-area fabrication of metasurface microstructures, and difficulties in high-density integration.

[0005] Based on existing asymmetric FP cavity structure designs, achieving ultrathin infrared absorbers while avoiding the introduction of complex and difficult-to-integrate top-layer microstructures hinges on maximizing the light wave propagation phase within the intermediate dielectric cavity layer and the upper metal layer. The simplest and most effective way to achieve this is to significantly increase the refractive index of the corresponding films. Simultaneously, the extinction coefficients of the dielectric layer and the upper metal layer must be carefully balanced; the former should be close to zero, while the latter should not be excessively large. This is to satisfy the resonant destructive phase of the light wave within the dielectric cavity and the impedance matching of the films, thereby obtaining high absorption characteristics. Therefore, finding suitable high-refractive-index infrared dielectric materials and low-loss infrared high-refractive-index metal materials has become a pressing challenge in the design of ultrathin infrared absorbers.

[0006] For the realization of high refractive index materials in the infrared dielectric layer, existing infrared transparent dielectric materials such as pure silicon and germanium have relatively high refractive indices of 3.4 and 4.0, respectively, but their refractive indices are close to the theoretical limit (Hyungki Shim, Francesco Monticone, and Owen D. Miller. Fundamental Limits to the Refractive Index of Transparent Optical Materials. Advanced Materials. 2021, 33, 2103946). As a thickness-dominant layer, the refractive index of the dielectric layer needs to be further increased to significantly reduce the thickness of the absorber. Based on the advantages of metamaterial microstructures in controlling the equivalent refractive index of materials, artificially introducing metallic microstructures into the dielectric material for modification can overcome the limitations of the refractive index of existing natural materials. Furthermore, by flexibly designing microstructures, the degree of freedom in controlling absorption performance will also be greatly improved. At present, the photolithography-free process for obtaining novel high refractive index materials in the infrared band by introducing microstructures into the dielectric layer mainly focuses on the colloidal self-assembly of Au nanostructures. This is due to the advantages of colloidal self-assembly in the preparation of small gaps and the excellent chemical inertness and process compatibility of Au itself. However, due to the low refractive index of colloidal media, it is currently difficult for such materials to exceed 4.5 in the broadband infrared band. Furthermore, the complex synthesis process and the difficulty in achieving large-area integrated fabrication remain prominent issues. Therefore, obtaining a high-refractive-index medium with embedded microstructures possessing broadband low dispersion, and solving the problems of difficult controllable fabrication and film integration, are key to constructing ultrathin absorbers using high-refractive-index metamaterials in the broadband infrared band.

[0007] For the realization of infrared high-refractive-index, low-loss metallic materials, materials possessing both a wide infrared wavelength, high refractive index, and a small extinction coefficient are extremely rare in nature, making it difficult to obtain a suitable upper metal for asymmetric FP structures in infrared absorbers. Bismuth metal exhibits a high refractive index of around 8 in the infrared 2-10 μm band, along with low dispersion and a small extinction coefficient, showing potential for inclusion in structures. However, considering the nanometer-scale thickness of the upper metal layer itself, relying on the existing refractive index of elemental bismuth, the phase accumulation of light within it and the final thinning effect remain limited. Therefore, further optimizing the refractive index of the top metal is key to enhancing the ultrathinning of absorbers. Summary of the Invention

[0008] In view of the above, the purpose of this invention is to provide a method for preparing an ultrathin absorber with high infrared absorption. The preparation method is simple and efficient, and the obtained ultrathin absorber has high infrared absorption characteristics.

[0009] To achieve the above-mentioned objectives, an embodiment provides an ultrathin absorber with high infrared absorption, comprising, from bottom to top, a metal substrate layer, a metamaterial dielectric layer, and a composite metal layer;

[0010] The metal substrate is an infrared highly reflective metal with a thickness greater than 100 nm.

[0011] The metamaterial dielectric layer is a semiconductor embedded vertical metal nanowire array with a thickness of 40-300 nm.

[0012] The composite metal layer is a bismuth-based composite metal with a thickness of 10-80 nm.

[0013] Preferably, the ultrathin absorber with high infrared absorption further includes another metamaterial dielectric layer, which is deposited on the composite metal layer. The other metamaterial dielectric layer is a semiconductor embedded vertical metal nanowire array with a thickness of 40-300 nm.

[0014] The metal substrate is gold, silver, aluminum, or silicon, which have high infrared reflectivity, or is suitable for testing and characterization.

[0015] In the aforementioned metamaterial dielectric layer and another metamaterial dielectric layer, the semiconductor is any one of silicon, germanium, selenium, and tellurium, and the metal nanowires are any one of gold, silver, copper, aluminum, and rhodium nanowires. The volume percentage of the metal nanowires is 5%-40%, the spacing between the metal nanowires is 2-6 nm, and the diameter is 3-7 nm. In the infrared band, semiconductors possess the requirements of high refractive index, low absorption, and low dispersion as a dielectric layer for broadband infrared absorbers. To further increase the refractive index of the dielectric and achieve ultrathin absorbers, this invention designs the introduction of microstructures into the semiconductor to construct a metal nanowire array-semiconductor composite metamaterial dielectric layer. The metal is selected from low-loss metals such as gold, silver, or aluminum to reduce unnecessary absorption in the metamaterial dielectric layer. By growing a vertical metal nanowire array-semiconductor parent phase through magnetron co-sputtering self-assembly, the diameter, spacing, and length of the nanowires can be flexibly controlled, further achieving control over the refractive index and thickness of the metamaterial dielectric layer, thus realizing frequency-selective absorption.

[0016] Preferably, in the metamaterial dielectric layer and the other metamaterial dielectric layer, the semiconductor is silicon, germanium, or tellurium, and the metal nanowires are gold, silver, or aluminum nanowires. The volume percentage of the metal nanowires is 5%-40%, the spacing between the metal nanowires is 2-6 nm, and the diameter is 3-7 nm. Based on the effective dielectric theory, due to the introduction of the metal nanowire microstructure and the high refractive index of the semiconductor parent phase, the metamaterial can achieve an increase in the material's equivalent refractive index, exhibiting an ultra-high refractive index of 4-8 in the infrared 2-10 μm range, thereby resulting in a large optical wave phase accumulation in the dielectric cavity layer. Compared to pure silicon materials, the metamaterial dielectric layer can achieve a thickness reduction of approximately 36%.

[0017] The bismuth-based composite metal is a composite metal of bismuth with gold, silver, copper, aluminum, or rhodium, with bismuth comprising 60%-98% by volume. This bismuth-based composite metal exhibits an ultra-high refractive index of 8-12 in the infrared 2-10 μm range. Based on the high refractive index characteristics of bismuth itself in the wide infrared band, by blending with other metals and controlling the metal volume percentage and thickness, the bismuth film structure is altered and the refractive index is increased. Ultimately, a metal layer with both ultra-high refractive index and film system matching in the wide infrared band is obtained, meeting the requirements for absorber thinning and high absorption.

[0018] The ultrathin absorber provided by this invention is a three-layer structure (metal / dielectric / metal substrate) or a four-layer structure (dielectric / metal / dielectric / metal substrate) consisting of a composite metal layer, one or two metamaterial dielectric layers, and a metal substrate layer. The thickness of each layer, the volume percentage of each component, and the diameter, length, and spacing of the nanowires in the metamaterial dielectric layer can all be controlled by adjusting experimental conditions. Based on the destructive interference of reflected light satisfying 4nd = λ, the thickness of the absorber can be significantly reduced by increasing the refractive index of each layer, especially the refractive index of the dielectric layer, which is the thickness-dominant layer. The overall thickness of this ultrathin absorber, excluding the substrate, is 100-400 nm, and the absorption band can be arbitrarily controlled between 1-15 μm.

[0019] To achieve the above-mentioned objective, the embodiment also provides a method for preparing the above-mentioned ultrathin absorber with high infrared absorption, comprising the following steps:

[0020] Under an argon atmosphere, the sputtering pressure was controlled at 0.1-0.5 Pa, and metal and semiconductor were used as co-sputtering targets, with the sputtering power density of the metal target controlled at 0.1-5 W / cm². 2 The sputtering power density of semiconductor targets is 3-10 W / cm². 2 Additional power density is 1-3 W / cm³ 2 A metamaterial dielectric layer is obtained by magnetron sputtering deposition on a metal substrate with argon plasma bombardment energy of not less than -30eV.

[0021] Using bismuth and another metal as bimetallic targets, the sputtering power density of the bimetallic targets was controlled to be 0.1-5 W / cm². 2 A composite metal layer is deposited on a metamaterial dielectric layer.

[0022] This preparation method involves preparing a metamaterial dielectric layer by co-sputtering a metal-semiconductor target under appropriate argon plasma-assisted bombardment, and preparing a composite metal layer by co-sputtering a bismuth-metal target. This allows for the fabrication of an infrared high-absorption ultrathin absorber composed of a composite metal layer and a metamaterial dielectric layer on a metal substrate. The preparation method is simple and efficient.

[0023] To prepare an ultrathin absorber comprising two metamaterial dielectric layers, the preparation method further includes depositing another metamaterial dielectric layer on the composite metal layer. Specifically, the deposition is performed using the same method as the first metamaterial dielectric layer, i.e., using metal and semiconductor as co-sputtering targets, and controlling the sputtering power density of the metal target to be 0.1-5 W / cm². 2 The sputtering power density of semiconductor targets is 3-10 W / cm². 2 Additional power density is 1-3 W / cm³ 2 Argon plasma bombardment assistance with an energy of not less than -30eV.

[0024] During the fabrication process, metal targets are driven by pulsed, radio frequency (RF), or DC power supplies, while semiconductor targets are driven by pulsed, RF, or DC power supplies. Metal targets are highly reactive and easily sputtered, so lower power is preferable; therefore, the sputtering power density range is 0.1-5 W / cm². 2 The semiconductor target is sputtered with high power, therefore the sputtering power density ranges from 3 to 10 W / cm². 2 Argon plasma bombardment is employed, with a power density ranging from 1 to 3 W / cm². 2 Furthermore, the argon-argon plasma bombardment energy is not less than -30eV. In addition, the distance between the target and the metal substrate is 70-100mm. This avoids the excessive sputtering energy caused by too small a target-substrate distance, which would lead to severe backsputtering and excessive sputtering rate, affecting the film quality. It also avoids the excessively large target-substrate distance, which would lead to too low sputtering atomic energy, resulting in reduced film-substrate adhesion and sputtering efficiency.

[0025] When the metal target is bismuth, gold, silver, or aluminum, the sputtering power density of the target is 0.1-4 W / cm². 2 When the semiconductor target material is silicon, germanium, or tellurium, which possesses both high refractive index and low dispersion in the infrared, the power range used is 3-7 W / cm². 2 .

[0026] The preparation method further includes pre-treatment of the metal substrate, specifically including ultrasonic cleaning of the substrate with acetone, alcohol and deionized water in sequence, followed by heating desorption and plasma sputtering cleaning.

[0027] This invention achieves frequency-selective absorption of the absorber in the 1-15 μm wavelength range, with a total thickness excluding the substrate of 100-400 nm. By appropriately controlling and combining the substrate, metal target, semiconductor target, and their respective power ranges—for example, through co-sputtering growth of metal nanowires and dielectrics with silver and silicon, or gold and germanium, or co-sputtering growth of composite metal layers with bismuth and gold, or bismuth and silver—flexible control of the absorption peak can be achieved. Furthermore, by adding a metamaterial dielectric layer to the top layer of the composite metal layer / metamaterial dielectric layer / metal substrate structure, a new optical cavity can be formed, achieving bimodal broadband absorption and significantly expanding the freedom of frequency-selective absorption control.

[0028] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0029] (1) For metamaterial dielectric layers, when the incident light is perpendicular to the material surface, the extreme value of its refractive index in the near-infrared band can reach above 7, and the refractive index in the mid- and far-infrared band can remain almost unchanged at a certain value between 4 and 8, which significantly enhances the accumulation of light wave phase. As an infrared transparent medium, it can effectively achieve the requirements of broadband, low dispersion, high refractive index and low extinction coefficient, and has a significant effect on ultrathinning in the application of infrared absorbers.

[0030] (2) For composite metal layers, an ultra-high refractive index value of 8-12 can be maintained in the mid-infrared band, and the thickness is only 10-80nm. In addition to achieving effective thinning of the absorber, it has a significant effect on film system matching, thereby achieving high absorption characteristics and providing material support for the construction of new ultra-thin infrared absorbers.

[0031] (3) The absorber of this invention has a high degree of freedom in adjustment. According to the absorption requirements of the target band, the thickness of the composite metal layer and the metamaterial dielectric layer and the volume percentage of each component can be adjusted separately. In addition, the absorption band can be broadened by stacking a metamaterial dielectric layer on the composite metal layer / metamaterial dielectric layer / metal substrate structure, so as to realize the application of multi-peak high absorption.

[0032] (4) Compared with traditional ultrathin absorbers that only design the top metal microstructure or strengthen phase accumulation only in the dielectric layer, the present invention constructs an FP cavity based on a high refractive index metamaterial medium and a high refractive index composite metal top layer, combining an effective local light field, increasing phase accumulation in each layer and film matching design, thereby greatly realizing the ultrathinness and high absorption of the entire infrared absorber.

[0033] (5) Unlike traditional methods of introducing micro-nano structures into a medium, such as photolithography and solution self-assembly growth, this invention uses magnetron sputtering to directly grow the metamaterial dielectric layer and the entire absorber. This method is not only simple and low-cost, but also very suitable for large-area production. Furthermore, by simply adjusting the deposition parameters, the microstructure can be flexibly controlled, thereby enabling the absorber to obtain frequency-selective high absorption characteristics.

[0034] (6) The present invention has a wide range of choices for metal and semiconductor materials. Appropriate materials can be selected for preparation according to different refractive index and thickness requirements. The range of substrate materials is wide. The materials can be selected not only gold, silver or aluminum, but any low-cost metal with high infrared reflectivity can be used, which has a positive promoting effect on the large-area application of absorbers. Attached Figure Description

[0035] 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 only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 A schematic diagram of the structure of the ultrathin absorber with high infrared absorption provided by the present invention;

[0037] Figure 2 This is a TEM image of the cross-section of the ultrathin infrared high-absorption absorber prepared in Example 1;

[0038] Figure 3 The comparison shows the absorption spectra of the infrared high-absorption ultrathin absorber prepared in Example 1 with those of the sample without the composite metal layer (metamaterial dielectric layer / metal substrate).

[0039] Figure 4 The refractive index of the silver nanowire-silicon composite metamaterial dielectric layer in the infrared high-absorption ultrathin absorber prepared in Example 1 is compared with that of pure silicon.

[0040] Figure 5 The refractive index of the bismuth-silver composite metal layer in the infrared high-absorption ultrathin absorber prepared in Example 1 is compared with that of pure bismuth.

[0041] Figure 6 The refractive index of the silver nanowire-silicon composite metamaterial dielectric layer in the infrared high-absorption ultrathin absorber prepared in Example 2;

[0042] Figure 7 The refractive index of the bismuth-silver composite metal layer in the infrared high-absorption ultrathin absorber prepared in Example 2;

[0043] Figure 8 The absorption spectrum of the infrared high-absorption ultrathin absorber prepared in Example 2;

[0044] Figure 9 This is a cross-sectional SEM image of the ultrathin absorber with high infrared absorption prepared in Example 3;

[0045] Figure 10 The absorption spectrum of the infrared high-absorption ultrathin absorber prepared in Example 3;

[0046] Figure 11 The absorption spectrum of the infrared high-absorption ultrathin absorber prepared in Example 4 is shown. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of this invention.

[0048] To achieve ultrathin infrared high-absorption absorbers, the embodiments provide an ultrathin absorber and its preparation method. First, based on the high infrared refractive index, low dispersion and stability of semiconductors such as silicon, germanium, selenium or tellurium, they are selected as the dielectric parent phase. Using a simple physical deposition process, metal microstructures are introduced into it for modification, further improving the refractive index of the material and enhancing the phase accumulation of light waves in the dielectric cavity layer, thereby achieving ultrathinness.

[0049] Secondly, for the metal top layer material, based on the high refractive index, low dispersion and small extinction coefficient of bismuth in the infrared 2-10μm band, the embodiments combine bismuth with other metals to obtain a new material with a higher refractive index, thereby promoting further optimization of the absorber thickness and the matching of film structure.

[0050] Furthermore, in order to achieve a high absorption response of the ultrathin absorber to a single wavelength band and to obtain broadband absorption characteristics in practical applications, an additional metamaterial dielectric layer is added to the above-mentioned composite metal layer / metamaterial dielectric layer / metal substrate structure. Two dielectric optical cavities are formed above and below the composite metal layer to broaden the absorption wavelength band. This enables the ultrathin absorber to achieve frequency-selective absorption in both a single wavelength band and a broadband band.

[0051] The ultrathin absorber and its preparation method are described in detail below with reference to specific embodiments:

[0052] Example 1

[0053] First, the substrate was cleaned by ultrasonically cleaning the metal substrate and silicon wafer sequentially with acetone, ethanol, and deionized water for 15 minutes each to remove surface contaminants. After cleaning, the substrate was dried with nitrogen and fixed on a substrate tray, with the target 85 mm away from the metal substrate. The tray was then loaded into the preparation chamber of the magnetron sputtering equipment, and a vacuum was evacuated sequentially using a mechanical pump and a molecular pump until the vacuum gauge reading reached 2*10⁻⁶. -4 Below Pa; open the argon gas path and introduce argon gas flow to maintain the deposition chamber pressure at 0.1-0.5 Pa, apply bias voltage to clean the substrate for 10 min; after cleaning, adjust the deposition chamber pressure to 0.3 Pa and control the silver target sputtering power density to 0.72 W / cm². 2 The sputtering power of the silicon target is 5.5 W / cm. 2 With the aid of argon plasma bombardment, its power density is 2W / cm³. 2 The bombardment energy was approximately -70 eV, and sputtering began with a deposition time of 2 hours and 30 minutes. Afterward, the silicon target and bias drive power supply were turned off. A bismuth target sputtering power density of 0.85 W / cm² was applied. 2 Silver target sputtering power density 0.6 W / cm² 2 Deposition was carried out for 2 minutes. After completion, the driving power supplies for the silver and bismuth targets were turned off. This yielded an ultrathin absorber with high infrared absorption. A schematic diagram of the obtained absorber structure is shown below. Figure 1 As shown.

[0054] The cross-sectional morphology of the above-mentioned thin film samples was observed and analyzed using transmission electron microscopy (TEM). Figure 2 The cross-sectional TEM morphology of the infrared ultrathin absorber in Example 1 is given, from... Figure 2 The cross-section clearly shows a composite metal layer, a metamaterial dielectric layer, and a metal substrate. The bismuth-silver composite metal layer is 10-20 nm thick, with bismuth comprising 87% of its volume. The silicon-silver metamaterial dielectric layer is 130-140 nm thick, with silver nanowires vertically and periodically embedded within the silicon dielectric. The average diameter of the silver nanowires is 4.4 nm, the inter-nanowire spacing is 2.9 nm, and the volume percentage of the metal nanowires is 29%.

[0055] Figure 3The absorption spectrum of the infrared ultrathin absorber in Example 1 is shown. Subtracting the measured infrared Fourier reflectance spectrum (absorption spectrum) of the sample from 100% reveals that the peak absorption rate of the ultrathin absorber obtained in Example 1 reaches approximately 90.8% at around 3.7 μm. This is due to the FP resonance effect of the composite metal layer / metamaterial dielectric layer / metal substrate structure, which causes destructive interference of reflected light, resulting in high absorption. In contrast, under the same conditions, the absorption peak of the sample composed only of the metamaterial dielectric layer and the metal substrate is only around 3.1 μm, with an absorption peak of approximately 90.6%. This indicates that the composite metal layer / metamaterial dielectric layer / metal substrate structure can significantly redshift the absorption peak, meaning that the light wave accumulates more phase in the film layer, allowing for absorption at longer wavelengths and achieving effective thinning. Furthermore, the addition of the composite metal layer in the sample obtained in Example 1 has a relatively small impact on the absorption peak intensity, which is beneficial for film system matching.

[0056] The refractive index of the silver nanowire-silicon metamaterial dielectric layer in the ultrathin absorber with high infrared absorption in Example 1 was fitted by ellipticity testing of the experimental sample. The results are as follows: Figure 4 As shown, the refractive index of this metamaterial is significantly improved compared to pure silicon. At this filling rate, the obtained refractive index has a maximum value of 5.0 at 2μm and is not less than 4.6 in the band greater than 2μm.

[0057] The refractive index of the bismuth-silver composite metal layer in the ultrathin absorber with high infrared absorption in Example 1 was fitted by ellipticity testing of the experimental sample. The results are as follows: Figure 5 As shown, the refractive index of this composite metal is significantly improved compared to pure bismuth. At this filling rate, the obtained refractive index remains around 11 in the range of 2-10 μm, demonstrating ultra-high refractive index and low dispersion characteristics.

[0058] Example 2

[0059] First, the substrate was cleaned by ultrasonically cleaning it with acetone, ethanol, and deionized water for 15 minutes each to remove surface contaminants. After cleaning, the substrate was dried with nitrogen and fixed on a substrate tray, with the target 85 mm away from the substrate. The tray was then loaded into the preparation chamber of the magnetron sputtering equipment, and a vacuum was evacuated sequentially using a mechanical pump and a molecular pump until the vacuum gauge reading reached 2*10⁻⁶. -4 Below Pa; open the argon gas path and introduce argon gas flow to maintain the deposition chamber pressure at 0.1-0.5 Pa, apply bias voltage to clean the substrate for 10 min; after cleaning, adjust the deposition chamber pressure to 0.3 Pa and control the silver target sputtering power density to 0.68 W / cm². 2 The sputtering power of the silicon target is 5.5 W / cm. 2 With the aid of argon plasma bombardment, its power density is 2.2 W / cm³. 2The bombardment energy was approximately -78 eV, and sputtering began with a deposition time of 2 hours and 30 minutes. Afterward, the silver target, silicon target, and bias drive power supply were turned off. A bismuth target sputtering power density of 0.85 W / cm² was applied. 2 Silver target sputtering power density: 0.57 W / cm³ 2 Deposition was carried out for 2 minutes. After completion, the driving power supplies for the silver and bismuth targets were turned off. This yielded an ultrathin absorber with high infrared absorption.

[0060] In the ultrathin absorber prepared in Example 2, the bismuth-silver composite metal layer has a thickness of 10-20 nm, and the bismuth volume percentage is 84%. The silicon-silver metamaterial dielectric layer has a thickness of 130-140 nm, and silver nanowires are vertically and periodically embedded in the silicon dielectric. The average diameter of the silver nanowires is 4.1 nm, the spacing between the nanowires is 2.9 nm, and the volume percentage of the metal nanowires is 25%.

[0061] The refractive index of the silver nanowire-silicon metamaterial dielectric layer in the ultrathin absorber with high infrared absorption in Example 2 was fitted by ellipticity testing of the experimental sample. The results are as follows: Figure 6 As shown, the refractive index of the metamaterial is lower than that of Example 1. This is because the silver nanowire filling rate of the silver nanowire-silicon metamaterial dielectric layer in Example 2 is reduced, and the corresponding phase accumulation in the dielectric layer is reduced.

[0062] The refractive index of the bismuth-silver composite metal layer in the ultrathin absorber with high infrared absorption in Example 2 was fitted by ellipticity testing of the experimental sample. The results are as follows: Figure 7 As shown, the refractive index of the composite metal is lower than that of Example 1, which is due to the increased bismuth metal filling rate of the bismuth-silver composite metal layer in Example 2.

[0063] Figure 8 The absorption spectrum of the infrared ultrathin absorber in Example 2 is shown. Subtracting the measured infrared Fourier reflectance spectrum (absorption spectrum) of the sample from 100% reveals that the peak absorption rate of the sample obtained in Example 2 reaches approximately 96.0% at around 3.4 μm. This is due to the FP resonance effect of the composite metal layer / metamaterial dielectric layer / metal substrate structure, which causes destructive interference of the reflected light. The different refractive indices of the film layers are more well-matched compared to Example 1, resulting in higher absorption in Example 2.

[0064] Comparing Examples 1 and 2, the refractive index of the composite metal layer can be changed by adjusting the volume percentage of the bismuth-based metal, and the refractive index of the metamaterial dielectric layer can be changed by adjusting the filling rate of the metal nanowires, thereby achieving a significant improvement in the degree of freedom in controlling the absorption performance.

[0065] Example 3

[0066] First, the substrate was cleaned by ultrasonically cleaning the metal substrate and silicon wafer sequentially with acetone, ethanol, and deionized water for 15 minutes each to remove surface contaminants. After cleaning, the substrate was dried with nitrogen and fixed on a substrate tray, with the target 85 mm away from the metal substrate. The tray was then loaded into the preparation chamber of the magnetron sputtering equipment, and a vacuum was evacuated sequentially using a mechanical pump and a molecular pump until the vacuum gauge reading reached 2*10⁻⁶. -4 Below Pa; open the argon gas path and introduce argon gas flow to maintain the deposition chamber pressure at 0.1-0.5 Pa, apply bias voltage to clean the substrate for 10 min; after cleaning, adjust the deposition chamber pressure to 0.3 Pa and control the silver target sputtering power density to 0.62 W / cm². 2 The sputtering power of the silicon target is 6.5 W / cm. 2 With the aid of argon plasma bombardment, its power density is 2W / cm³. 2 The bombardment energy was approximately -70 eV, and sputtering began with a deposition time of 50 minutes. Afterward, the silicon target and bias drive power supply were turned off. A bismuth target sputtering power density of 0.85 W / cm² was applied. 2 Silver target sputtering power density: 0.4 W / cm² 2 Deposition was carried out for 18 minutes. After completion, the bismuth target drive power was turned off. A silver target sputtering power density of 0.58 W / cm² was applied. 2 The sputtering power of the silicon target is 6.2 W / cm. 2 With the aid of argon plasma bombardment, its power density is 1.8 W / cm³. 2 The bombardment energy was approximately -62 eV, and deposition lasted for 3 hours and 30 minutes. After completion, the silver target, silicon target, and bias drive power supply were turned off. This yielded an ultrathin absorber with high infrared absorption.

[0067] The cross-sectional morphology of the above-mentioned thin film samples was observed and analyzed using scanning electron microscopy (SEM). Figure 9 The cross-sectional SEM morphology of the infrared ultrathin absorber in Example 3 is shown, as follows: Figure 9 As can be seen in the cross-section, there are metamaterial dielectric layer, composite metal layer, metamaterial dielectric layer and silicon substrate. The upper silver nanowire-silicon metamaterial dielectric layer has a thickness of 150-160 nm and the volume percentage of metal nanowires is 12%; the bismuth-silver composite metal layer has a thickness of 60-70 nm and the volume percentage of bismuth in it is 93%; the lower silver nanowire-silicon metamaterial dielectric layer has a thickness of 50-60 nm and the volume percentage of metal nanowires is 15%.

[0068] Figure 10The image shows the absorption spectrum of the infrared ultrathin absorber in Example 3. Subtracting the measured infrared Fourier reflectance spectrum (absorption spectrum) of the sample from 100% reveals that the sample obtained in Example 1 exhibits absorption peaks at 3.0 and 7.6 μm, with peak intensities of approximately 81.7% and 89.2%, respectively. This is because the metamaterial dielectric layer added to the composite metal layer / metamaterial dielectric layer / metal substrate FP structure creates a new optical cavity, promoting the formation of new absorption peaks. This results in the absorber exhibiting significant absorption across a broad infrared band of 2-10 μm.

[0069] As can be seen from the above, by changing the experimental parameters and effectively controlling the structure, thickness and composition of each layer of the absorber, a high-absorption ultrathin infrared absorber can be obtained.

[0070] Example 4

[0071] First, the substrate was cleaned by ultrasonically cleaning it with acetone, ethanol, and deionized water for 15 minutes each to remove surface contaminants. After cleaning, the substrate was dried with nitrogen and fixed on a substrate tray, with the target 85 mm away from the substrate. The tray was then loaded into the preparation chamber of the magnetron sputtering equipment, and a vacuum was evacuated sequentially using a mechanical pump and a molecular pump until the vacuum gauge reading reached 2*10⁻⁶. -4 Below Pa; open the argon gas path and introduce argon gas flow to maintain the deposition chamber pressure at 0.1-0.5 Pa, apply bias voltage to clean the substrate for 10 min; after cleaning, adjust the deposition chamber pressure to 0.3 Pa and control the aluminum target sputtering power density to 0.7 W / cm². 2 The sputtering power of the germanium target is 6W / cm. 2 With the aid of argon plasma bombardment, its power density is 2W / cm³. 2 The bombardment energy was approximately -70 eV, and sputtering began with a deposition time of 45 minutes. Afterward, the aluminum target, germanium target, and bias drive power supply were turned off. A bismuth target sputtering power density of 0.85 W / cm³ was applied. 2 Gold sputtering power density: 0.4 W / cm³ 2 Deposition was carried out for 17 minutes. Afterwards, the power supplies for the gold and bismuth targets were turned off. An aluminum target sputtering power density of 0.55 W / cm² was applied. 2 Germanium target sputtering power 6.2W / cm 2 With the aid of argon plasma bombardment, its power density is 1.8 W / cm³. 2 The bombardment energy was approximately -62 eV, and deposition lasted for 4 hours. After completion, the aluminum target, germanium target, and bias drive power supply were turned off. This yielded an ultrathin absorber with high infrared absorption.

[0072] In the ultrathin absorber prepared in Example 4, the thickness of the upper aluminum nanowire-germanium metamaterial dielectric layer is 165-175 nm, and the volume percentage of the metal nanowires is 12%; the thickness of the bismuth-gold composite metal layer is 50-60 nm, and the volume percentage of bismuth in it is 93%; the thickness of the lower aluminum nanowire-germanium metamaterial dielectric layer is 40-50 nm, and the volume percentage of the metal nanowires is 32%.

[0073] Figure 11 The absorption spectrum of the infrared ultrathin absorber in Example 4 is shown. Subtracting the infrared Fourier reflectance spectrum (absorption spectrum) of the sample from 100% reveals that the sample obtained in Example 4 exhibits absorption peaks at 1.9, 3.9, and 7.9 μm, with absorptivity of approximately 82.2%, 77.2%, and 96.5%, respectively. This is because the metamaterial dielectric layer added to the composite metal layer / metamaterial dielectric layer / metal substrate FP structure creates a new optical cavity, promoting the formation of a new absorption peak at 3.9 μm. Furthermore, the relatively large thickness of the upper metamaterial dielectric layer results in higher-order resonance peaks at short wavelengths, enabling the absorber to possess significant absorption characteristics across a broad infrared band of 2-10 μm.

[0074] Examples 1-4 demonstrate that infrared ultrathin absorbers with different absorption responses can be easily obtained by using different combinations of bismuth-based composite metal layers and different metal nanowire-semiconductor metamaterial dielectric layers.

[0075] Based on the above embodiments, through material design and structural optimization, both the dielectric layer and the upper metal layer in the asymmetric FP cavity structure are redesigned, resulting in a further reduction in the thickness of the entire absorber compared to existing absorbers, achieving an ultra-thin effect and enabling frequency-selective high absorption in a wide high-frequency infrared band. Simultaneously, a simple continuous deposition process allows for the controllable fabrication of the entire absorber, including the metamaterial dielectric layer.

[0076] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An ultrathin absorber with high infrared absorption, characterized in that, It includes, from bottom to top, a metal substrate layer, a metamaterial dielectric layer, and a composite metal layer; The metal substrate is an infrared highly reflective metal with a thickness greater than 100 nm. The metamaterial dielectric layer is a semiconductor-embedded vertical metal nanowire array with a thickness of 40-300 nm. The composite metal layer is a bismuth-based composite metal with a thickness of 10-80 nm. The bismuth-based composite metal is a composite metal of bismuth with gold, silver, copper, aluminum or rhodium. The volume percentage of bismuth in the bismuth-based composite metal is 60%-98%. The bismuth-based composite metal has an ultra-high refractive index of 8-12 in the infrared 2-10 μm range. An FP resonant cavity was constructed based on a high-refractive-index metamaterial dielectric layer and a high-refractive-index composite metal layer.

2. The ultrathin absorber with high infrared absorption according to claim 1, characterized in that, It also includes another metamaterial dielectric layer, which is deposited on the composite metal layer. The other metamaterial dielectric layer is a semiconductor embedded vertical metal nanowire array with a thickness of 40-300 nm.

3. The ultrathin absorber with high infrared absorption according to claim 1 or 2, characterized in that, In the metamaterial dielectric layer and the other metamaterial dielectric layer, the semiconductor is any one of silicon, germanium, selenium and tellurium, and the metal nanowire is any one of gold, silver, copper, aluminum and rhodium nanowire.

4. The ultrathin absorber with high infrared absorption according to claim 1 or 2, characterized in that, In the metamaterial dielectric layer and another metamaterial dielectric layer, the volume percentage of metal nanowires is 5%-40%, the spacing between metal nanowires is 2-6 nm, and the diameter is 3-7 nm.

5. A method for preparing an ultrathin absorber with high infrared absorption as described in any one of claims 1-4, characterized in that, Includes the following steps: Under an argon atmosphere, the sputtering pressure was controlled at 0.1-0.5 Pa, and metal and semiconductor were used as co-sputtering targets, with the sputtering power density of the metal target controlled at 0.1-5 W / cm². 2 The sputtering power density of semiconductor targets is 3-10 W / cm². 2 The additional power density is 1-3 W / cm³ 2 A metamaterial dielectric layer is obtained by magnetron sputtering deposition on a metal substrate with argon plasma bombardment energy of not less than -30 eV. Using bismuth and another metal as dual-metal targets, the sputtering power density of the dual-metal targets was controlled to be 0.1-5 W / cm². 2 A composite metal layer is deposited on a metamaterial dielectric layer.

6. The method for preparing an ultrathin absorber with high infrared absorption as described in claim 5, characterized in that, The method further includes: depositing another metamaterial dielectric layer on the composite metal layer, specifically, using metal and semiconductor as co-sputtering targets, and controlling the sputtering power density of the metal target to be 0.1-5 W / cm². 2 The sputtering power density of semiconductor targets is 3-10 W / cm². 2 The additional power density is 1-3 W / cm³ 2 Argon plasma bombardment assistance with an energy of not less than -30 eV.

7. The method for preparing an ultrathin absorber with high infrared absorption as described in claim 5, characterized in that, When the metal target is bismuth, gold, silver, or aluminum, the sputtering power density of the metal target is 0.1-4 W / cm². 2 When the semiconductor target is silicon, germanium, or tellurium, the sputtering power density of the semiconductor target is 3-7 W / cm². 2 .

8. The method for preparing an ultrathin absorber with high infrared absorption as described in claim 5, characterized in that, The distance between the target and the metal substrate is 70-100 mm.

9. The method for preparing an ultrathin absorber with high infrared absorption as described in claim 5, characterized in that, It also includes pretreatment of the metal substrate, specifically including ultrasonic cleaning of the substrate with acetone, alcohol and deionized water in sequence, followed by heating desorption and plasma sputtering cleaning.

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