Polyvinyl alcohol composite film containing 1t-mo se2 coated w o3 nanosheet, preparation method and application thereof

Abstract

The present application relates to a kind of polyvinyl alcohol composite film of molybdenum diselenide coated WO3 Nanosheet containing 1T-MoSe2, preparation method and application, the (100) face of the nanosheet of molybdenum diselenide containing 1T-MoSe2 synthesized by hydrothermal method and WO3 Nanosheet is combined to build the composite material of heterostructure, the composite material is dispersed in 10 wt% polyvinyl alcohol solution and is poured to obtain polymer film, when the thickness of composite film sample is 500 µm, the material of optimal ratio shows effective shielding efficiency (shielding efficiency is greater than or equal to 10dB) in the whole test range of 0.2-1.8THz, shielding efficiency can reach 71.48 dB at 1.62 THz, and the average terahertz shielding efficiency reaches 43.03 dB.The material has the advantages such as light, ultra-thin and strong absorption, and has important value in the fields such as microelectronic device terahertz signal shielding, stealth coating and the like.

Description

Technical Field

[0001] This invention belongs to the field of terahertz wave absorption, specifically relating to a composite material of molybdenum diselenide grown on tungsten trioxide nanosheets as a filler, a polymer film based on polyvinyl alcohol, and its application in terahertz wave absorption. Background Technology

[0002] Terahertz waves, located in a "vacuum zone" between infrared and microwave frequencies, possess significant advantages such as high bandwidth, high penetration, low energy, coherence, and fingerprint spectral characteristics, making them valuable in numerous important fields including life sciences, materials science, astronomy, atmospheric and environmental monitoring, communications, and national security. However, while the rapid development of high-frequency radio technology and the widespread use of electronic devices have brought great convenience to human life, the resulting electromagnetic pollution poses a serious threat to human health and can also damage the stability of precision electrical equipment. Furthermore, in the military field, the development of radar detection technology has led to severe radar-guided attacks on next-generation high-speed aircraft, significantly impacting their ability to penetrate defenses and survive on future battlefields. Therefore, the rapidly developing terahertz technology requires high-performance terahertz absorbers to suppress electromagnetic interference and achieve terahertz stealth. Terahertz wave absorbing materials can dissipate terahertz waves as heat within the material through various attenuation mechanisms. These materials need to meet properties such as low density, ultrathinness, and strong absorption to match the miniaturization and ultrathin coating technologies used in military and electronic products.

[0003] Metallic molybdenum diselenide (1T-MoSe2) sheets resemble graphene sheets and exhibit better intrinsic activity and conductivity compared to semiconductor molybdenum diselenide (2H-MoSe2). Their diameter is approximately 50 nm, while terahertz waves have significantly different wavelengths. This size difference makes resonant absorption an ineffective method for electromagnetic wave attenuation. WO3 possesses a unique octahedral crystal structure, readily undergoing lattice distortion under minor external stimuli. This distortion alters the crystal structure and local electron configuration of WO3, improving its electrochemical properties and conductivity. Furthermore, its abundant oxygen vacancies can modulate its dielectric loss capacity, making it a promising candidate for electromagnetic wave absorption. Polyvinyl alcohol (PVA) is a polymer with excellent optical properties and solubility. It also exhibits good flexibility, stretchability, and film-forming properties, making it an excellent choice for preparing polymer films.

[0004] Terahertz waves are composed of rapidly changing electric and magnetic fields. The key factor determining the terahertz wave dissipation performance of absorbing materials is the material's dielectric or magnetic loss capability. In the terahertz band, magnetic loss capability is relatively low, while dielectric loss is more prominent. The diversity and complexity of this loss process provide opportunities for seeking strong absorption. Single-component absorbers, due to their simple absorption mechanism and low conductivity, have difficult-to-control electromagnetic parameters, resulting in suboptimal terahertz absorption capabilities. To meet the requirements of ideal terahertz wave absorption, strategies such as constructing conductive networks, optimizing components, and building heterogeneous interfaces are typically employed to achieve adjustable electromagnetic parameters, controllable impedance matching, and significant synergistic effects between different components.

[0005] In recent years, research and development in terahertz artificial metamaterials has been rapid. Metamaterials essentially utilize various narrow-band absorbing materials and metallic materials through different design structures and assembly methods to absorb electromagnetic waves. While they can achieve controllable absorption of specific frequencies, most metamaterials struggle to achieve broadband absorption performance and suffer from complex designs and high device fabrication costs. On the other hand, research focuses on the intrinsic electromagnetic wave absorption of materials such as Mxene, carbon nanotubes, and graphene. These materials possess excellent conductivity, exhibiting good conductivity across a wide wavelength range. However, they can cause strong surface reflections due to impedance mismatch, significantly reducing terahertz absorption performance. Furthermore, with the development of microelectronic devices, the requirements for shielding materials are becoming increasingly stringent, making the need for ultrathin, lightweight, and highly absorbing thin-film materials urgent. Therefore, the application prospects for fabricating ultrathin, high-absorption, low-reflection terahertz shielding thin-film materials are very broad. Summary of the Invention

[0006] The purpose of this invention is to provide a polyvinyl alcohol composite film containing 1T-MoSe2 molybdenum diselenide coated with WO3 nanosheets, its preparation method, and its application in terahertz wave absorption, so as to solve the problem that existing terahertz wave absorbing materials are difficult to provide efficient polarization relaxation loss and have limited absorption performance.

[0007] The technical solution to achieve the objective of this invention is:

[0008] In the first aspect, a polyvinyl alcohol composite film containing molybdenum diselenide (MoSe2) coated with WO3 nanosheets is provided. The composite film uses a composite material with a unique heterostructure formed by molybdenum diselenide (MoSe2) attached to WO3 nanosheets as filler and polyvinyl alcohol (PVA) as matrix, wherein the MoSe2 is combined with the (001) crystal plane of WO3.

[0009] Preferably, the molybdenum diselenide containing 1T-MoSe2 has a nanosheet structure with a diameter of 30-50 nm.

[0010] Preferably, the WO3 nanosheets are thin-layer nanosheets with a planar diameter of 1-3 μm.

[0011] Preferably, a composite material with a unique heterostructure is formed by attaching molybdenum diselenide containing 1T-MoSe2 onto WO3 nanosheets, wherein the mass fraction of 1T-MoSe2 in the composite material is 30-50%, preferably 40%, and the mass fraction of WO3 is 20%.

[0012] Secondly, the present invention provides a method for preparing a polyvinyl alcohol composite film containing 1T-MoSe2 molybdenum diselenide coated with WO3 nanosheets as described in the first aspect, the steps of which are as follows:

[0013] Step 1: Dissolve sodium molybdate dihydrate and selenium powder in deionized water and stir mechanically for 1 hour. Sonicate until the solution is uniformly dispersed and record it as solution A.

[0014] Step 2: Add sodium borohydride in a molar ratio of 2 to 4 with sodium molybdate dihydrate to solution A, stir until homogeneous, transfer the solution to a high-pressure reactor, react at 200°C for 16 h, wash and vacuum dry to obtain molybdenum diselenide nanosheets containing 1T-MoSe2.

[0015] Step 3: Dissolve sodium tungstate dihydrate and sodium chloride in deionized water, adjust the pH of the solution, add the molybdenum diselenide nanosheets containing 1T-MoSe2 described in Step 2, stir evenly, transfer to a high-pressure reactor, and react at 180℃ for 24 hours.

[0016] Step 4: After the reaction is complete, the mixture is washed and vacuum dried to obtain a composite material containing 1T-MoSe2 molybdenum diselenide coated with WO3 nanosheets.

[0017] Step 5: Place the composite material from Step 4 into a polyvinyl alcohol (PVA) solution, stir until homogeneous, and then drop-cast the resulting mixed solution onto a smooth silicon wafer. Dry it in a vacuum environment at 35°C to form a film.

[0018] Preferably, in step 3, HCl is added dropwise to adjust the pH of the solution to 2.

[0019] Preferably, in step 5, the concentration of the PVA solution is 10 wt%, which results in better film-forming properties.

[0020] Preferably, in step 5, the composite material from step 4 accounts for 20% of the total mass of the mixed solution.

[0021] Thirdly, the present invention provides an application of the polyvinyl alcohol composite film containing 1T-MoSe2 molybdenum diselenide coated with WO3 nanosheets as described in the first aspect in terahertz wave absorption.

[0022] Preferably, the composite film has effective shielding performance (shielding performance ≥10dB) in the range of 0.2-1.8THz.

[0023] Preferably, the composite film has an average terahertz shielding effectiveness of not less than 43dB in the range of 0.2-1.8THz.

[0024] Fourthly, the present invention provides a terahertz absorbing material formed from a polyvinyl alcohol composite film containing molybdenum diselenide coated with WO3 nanosheets as described in the first aspect.

[0025] Fifthly, the present invention provides a terahertz absorber comprising a polyvinyl alcohol composite film containing molybdenum diselenide coated with WO3 nanosheets as described in the first aspect.

[0026] In a sixth aspect, the present invention also provides a stealth coating, which is formed by coating a polyvinyl alcohol composite film containing molybdenum diselenide-coated WO3 nanosheets as described in the first aspect onto a substrate.

[0027] Compared with the prior art, the beneficial effects of this invention are as follows: This invention relates to a polymer film containing 1T-MoSe2 molybdenum diselenide-coated tungsten trioxide nanosheets as filler and polyvinyl alcohol as matrix, and its application in terahertz shielding. The advantage of 1T-MoSe2 nanosheets over 2H-MoSe2 nanosheets is their stronger conductivity. The transition from the 2H phase to the 1T phase can significantly improve the electron transfer capability of MoSe2. Since the Fermi level of 1T-MoSe2 matches the energy level of tungsten trioxide, under periodic terahertz wave radiation, electrons from 1T-MoSe2 will be injected and released into the tungsten trioxide nanosheets. This minute external stimulus will change the electron cloud around the W atoms. The injection / release of electrons causes the electron cloud to change between W(VI) and W(VI). -The dielectric loss of the material was enhanced by varying the polarization relaxation between 0.2 and 1.8 THz, thereby improving the form of polarization relaxation and promoting terahertz wave absorption. Results showed that when the composite film sample thickness was 500 μm, the optimal material ratio exhibited effective shielding performance (≥10 dB) across the entire test range of 0.2–1.8 THz, reaching a shielding performance of 71.48 dB at 1.62 THz, with an average terahertz shielding performance of 43.03 dB. Furthermore, most of the shielding effectiveness came from absorption, with reflection shielding accounting for a very small proportion of the total shielding effectiveness. This material possesses advantages such as lightweight, ultrathinness, and strong absorption, making it valuable for applications such as terahertz signal shielding in microelectronic devices and stealth coatings. Attached Figure Description

[0028] Figure 1 (a) and (b) are scanning electron microscope images of semiconductor phase 2H-MoSe2 (MoSe2-O) nanosheets; (c) is an X-ray diffraction pattern of semiconductor phase 2H-MoSe2 (MoSe2-O) nanosheets; (d) is a diagram of the total shielding effectiveness of semiconductor phase MoSe2-O / PVA thin films in the range of 0.2-1.8 THz.

[0029] Figure 2 A schematic diagram showing the energy levels of the metallic phases 1T-MoSe2 and WO3 obtained through first-principles calculations.

[0030] Figure 3 (a) is a scanning electron microscope (SEM) image of WO3 nanosheets; (b) is a SEM image of a composite material containing MoSe2-2 / WO3; (c) is a SEM image of a localized MoSe2-2 / WO3 composite material; and (d) is an X-ray diffraction pattern of MoSe2-2 and the MoSe2-2 / WO3 composite material.

[0031] Figure 4 (a) shows the overall shielding effectiveness of the optimal ratio (MoSe2-2 / WO3) / PVA composite film with a thickness of 500 μm in the range of 0.2-1.8 THz; (b) shows the absorption shielding effectiveness of the optimal ratio (MoSe2-2 / WO3) / PVA composite film in the range of 0.2-1.8 THz.

[0032] Figure 5 In the figure, (a) represents the absorptivity of the optimal ratio of (MoSe2-2 / WO3) / PVA composite film with a thickness of 500 μm in the range of 0.2-1.8 THz; and (b) represents the reflectivity of the optimal ratio of (MoSe2-2 / WO3) / PVA composite film in the range of 0.2-1.8 THz.

[0033] Figure 6(a) shows the total shielding effectiveness of four composite films (MoSe2-0 / WO3) / PVA, (MoSe2-1 / WO3) / PVA, (MoSe2-2 / WO3) / PVA, and (MoSe2-3 / WO3) / PVA in the range of 0.2-1.8 THz, and (b) shows the average shielding effectiveness of composite films with different metal phase contents in the range of 0.2-1.8 THz. Detailed Implementation

[0034] The present application will be further described below with reference to specific embodiments.

[0035] It should be noted that terms such as "upper", "lower", "left", "right", and "middle" used in this specification are only for clarity of description and are not intended to limit the scope of implementation. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as within the scope of this application.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0037] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0038] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular variable.

[0039] As used herein, the term "at least one of..." is intended to be synonymous with "one or more of...". For example, "at least one of A, B, and C" explicitly includes only A, only B, only C, and combinations thereof. Concentration, amount, and other numerical data may be presented herein in range format. It should be understood that such range format is used only for convenience and brevity and should be flexibly interpreted to include not only the numerical values ​​explicitly stated as the limits of the range, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly stated. For example, a numerical range of about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to about 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only one numerical value, such as "less than about 4.5," which should be interpreted to include all the values ​​and ranges described above. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0040] This invention prepares molybdenum diselenide containing 1T-MoSe2 via a hydrothermal method. The content of 1T-MoSe2 in molybdenum diselenide is altered by controlling the amount of sodium borohydride, the reducing agent, during the reaction. This invention constructs a unique heterostructure composite by combining the (001) plane of tungsten trioxide with 1T-MoSe2. Ultrathin polymer films are prepared using tungsten trioxide nanosheets coated with molybdenum diselenide containing 1T-MoSe2 as fillers and polyvinyl alcohol (PVA) as the matrix. Due to the energy level matching between the Fermi level of 1T-MoSe2 and the conduction band of tungsten trioxide, periodic injection and release of electrons from the 1T-MoSe2 nanosheets to the tungsten trioxide nanosheets are promoted under the radiation of a periodically changing terahertz field. WO3 has a unique octahedral crystal structure and is prone to lattice distortion under relatively small external stimuli. This distortion can cause changes in the crystal structure and local electrons of WO3, realizing W(VI) and W(VI). -The polarization relaxation induced by valence reversal significantly enhances terahertz wave absorption performance. This invention prepares high-performance broadband absorbing materials based on the inherent physical properties of the materials themselves. The tungsten trioxide nanosheets coated with molybdenum diselenide (MoSe2) prepared in this invention exhibit excellent terahertz wave absorption performance in the 0.2-1.8 THz range due to the change in their inherent dipole moment. The terahertz wave absorbing film in the 0.2-1.8 THz range uses a 10 wt% PVA solution as the substrate, and the MoSe2 / WO3 composite nanomaterial containing the MoSe2 metal phase has a filling ratio of 20 wt%. The terahertz wave absorption and reflection performance in the 0.2-1.8 THz range are obtained from the transmission and reflection modes of terahertz time-domain spectroscopy. The electrical and magnetic properties of the material itself can be obtained through terahertz time-domain spectroscopy, and the refractive index, extinction coefficient, and absorption coefficient of the material can also be obtained through terahertz time-domain spectroscopy.

[0041] In previous work, this invention compared the effect of the WO3 content in 2H-MoSe2 / WO3 composite materials on terahertz absorption performance. MoSe2 / WO3 composite materials were prepared with WO3 mass contents of 10%, 20%, 30%, and 40%. The performance of the composite materials was tested by terahertz time-domain spectroscopy. It was found that the absorption performance of the MoSe2 / WO3 composite material was the best when the WO3 mass content was 20%. Therefore, in the MoSe2-containing molybdenum diselenide-coated tungsten trioxide nanosheet composite material involved in this invention, the mass content of tungsten trioxide was fixed at 20%. Only the influence of polymer films constructed from MoSe2-containing molybdenum diselenide-coated tungsten trioxide nanosheet composite materials with different proportions of the metallic phase on the terahertz absorption performance was considered.

[0042] The raw materials and instruments used in the embodiments are not specifically limited in their source; they can be purchased from the market or prepared according to conventional methods well known to those skilled in the art. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0043] Example 1

[0044] 0.242 g of sodium molybdate dihydrate and 0.158 g of selenium powder were added to 40 ml of deionized water along with different amounts of sodium borohydride (0.076 g, 0.152 g, 0.228 g, and 0.304 g), respectively. The mixture was sonicated for 30 minutes, followed by vigorous magnetic stirring for 50 minutes. When the molar ratio of sodium borohydride to sodium molybdate dihydrate was 1:1 (i.e., 0.076 g of sodium borohydride was added), a pure semiconductor phase 2H-MoSe2 (standard) was obtained hydrothermally. The reaction was denoted as MoSe2-0; when the molar ratio of sodium borohydride to sodium molybdate dihydrate was 2:1, i.e., 0.152 g of sodium borohydride was added, it was labeled as MoSe2-1; when the molar ratio of sodium borohydride to sodium molybdate dihydrate was 3:1, i.e., 0.228 g of sodium borohydride was added, it was labeled as MoSe2-2; and when the molar ratio of sodium borohydride to sodium molybdate dihydrate was 4:1, i.e., 0.304 g of sodium borohydride was added, it was labeled as MoSe2-3. The solution was then transferred to a Teflon-lined stainless steel autoclave. The autoclave was heated from room temperature (RT) to 200°C in a conventional oven at a rate of 20-25°C / min and maintained at the target temperature for 16 hours. After the reaction was complete, the oven was turned off and the mixture was allowed to cool naturally to room temperature. The product was then collected by centrifugation at 3000-6000 rpm and washed three times with deionized water and ethanol. Finally, the product was vacuum dried at 70°C.

[0045] The 2H-MoSe2, i.e. MoSe2-0 obtained in this embodiment, was tested using scanning electron microscopy and X-ray diffraction.

[0046] Scanning electron microscopy results as follows Figure 1 As shown in (a) and (b), the nanosheet structure of MoSe2-0 was generated via a hydrothermal method. During the reaction, the molar ratio of sodium borohydride to sodium molybdate dihydrate was 1:1, and the nanosheet diameter was approximately 50 nm. X-ray diffraction analysis of MoSe2-0 is shown below. Figure 1 As shown in (c), its peak position corresponds to the peak position of standard card PDF#29-0914, proving that no other impurities were generated. X-ray diffraction tests of MoSe2-2 are as follows... Figure 3 As shown in (d), the characteristic peaks at 12.7°, 31.7°, 38.3° and 56.2° correspond to the (002), (100), (103) and (110) surfaces, respectively.

[0047] Example 2

[0048] 0.4125g of sodium tungstate dihydrate powder and 0.145g of sodium chloride powder were dissolved in 40ml of deionized water. A small amount of hydrochloric acid was added to adjust the pH of the solution to pH=2. 1.16g of MoSe2-0, MoSe2-1, MoSe2-2 and MoSe2-3 prepared in Example 1 were added respectively. After sonication for 30 minutes, the mixture was magnetically stirred for 1 hour to uniformly disperse the precursor materials in the solution. The mixture was then transferred to a 50mL high-pressure reactor and reacted at 200℃ for 24 hours. The product was vacuum dried at 70℃ to obtain MoSe2-0 / WO3, MoSe2-1 / WO3, MoSe2-2 / WO3 and MoSe2-3 / WO3 composite materials with 1T-MoSe2 contents of 0%, 30%, 40% and 50% respectively.

[0049] Figure 2 The band structure diagram of the heterostructure composite constructed by coating WO3 nanosheets with molybdenum diselenide nanosheets containing 1T-MoSe2 is shown. First-principles calculations yielded a work function of 4.34 eV for 1T-MoSe2 and 5.04 eV for the WO3 (001) plane, with a bandwidth of 2.89 eV. As the 1T-MoSe2 and WO3 nanosheets form a heterojunction, the Fermi levels are unified, enabling the injection and release of electrons from the metallic molybdenum diselenide nanosheets to the tungsten trioxide (001) plane in a periodic electromagnetic field. This electron transfer can cause changes in the crystal structure and local electron configuration of WO3, altering the electron cloud distribution around the W atoms, and causing W(VI) and W(VI) to... - The dielectric loss performance of the material is improved by repeatedly changing between these parameters, thereby enhancing the terahertz absorption performance.

[0050] The MoSe2-2 / WO3 composite material prepared in this embodiment was analyzed by scanning electron microscopy and X-ray diffraction. At the same time, pure WO3 nanosheets (prepared by hydrothermal method) were also analyzed by scanning electron microscopy for comparison.

[0051] Electron microscopy images of pure WO3 nanosheets are as follows: Figure 3 As shown in (a), hydrothermal generation produces thin sheets with a diameter of approximately 1-3 μm. The electron microscopy image of the MoSe2-2 / WO3 composite material is shown below. Figure 3 As shown in (b) and (c), the larger tungsten trioxide nanosheets are coated with smaller molybdenum diselenide nanosheets containing 1T-MoSe2, indicating that the molybdenum diselenide nanosheets are well grown on the large tungsten trioxide sheets; the X-ray diffraction test of the MoSe2-2 / WO3 composite material is as follows. Figure 3 As shown in (d), the main peak positions are the same as those of MoSe2-2 nanosheets, with the only difference being crystallinity. Tungsten trioxide has good crystallinity, which is in good agreement with the standard card PDF#33-1387, and it does not contain any other impurities.

[0052] 1.1 g of polyvinyl alcohol powder was added to 10 ml of deionized water, and the solution was mechanically stirred at 90 °C for 1 hour until it gradually became a viscous liquid. 2.78 g of the prepared MoSe2-0 / WO3, MoSe2-1 / WO3, MoSe2-2 / WO3, and MoSe2-3 / WO3 composite materials were added separately, and the mixture was stirred continuously for 30 minutes to ensure uniform dispersion of the composite materials in a 10% PVA solution. A small amount of the solution was cast onto a smooth silicon wafer and dried at 35 °C under vacuum for 12 hours, finally yielding four polymer films: (MoSe2-0 / WO3) / PVA, (MoSe2-1 / WO3) / PVA, (MoSe2-2 / WO3) / PVA, and (MoSe2-3 / WO3) / PVA, with a film thickness of 500 μm.

[0053] The absorption performance of four polymer films in the 0.2-1.8 THz terahertz wave range was tested using a terahertz time-domain spectroscopy system. By using the transmission and reflection modes of the terahertz time-domain spectroscopy system, the overall shielding effectiveness, absorption shielding effectiveness, absorptivity, and reflectivity of the composite films were obtained.

[0054] Among them, the total shielding effectiveness of (MoSe2-2 / WO3) / PVA polymer film material in the range of 0.2-1.8THz and such Figure 4 As shown in (a): when the film thickness is 500 μm, the film exhibits effective shielding performance (shielding performance ≥10dB) throughout the entire test range of 0.2-1.8THz, and the shielding performance can reach 71.48dB at 1.65THz. Figure 4 (b) describes the absorption shielding effectiveness of the film. The absorption shielding effectiveness can reach 71.4 dB at 1.65 THz, which is almost the same as the total shielding effectiveness. Moreover, the effective shielding band occupies the entire test, proving that the shielding effectiveness of the film is dominated by absorption. Figure 5 Figure (a) describes the absorptivity of the thin film. In the range of 0.2–1.8 THz, the absorptivity is mostly around 99%, with a lower absorptivity of 93% at 1.72 THz. This is because the polymer PVA exhibits some reflection at 1.72 THz. Figure 5 (b) describes the reflectivity of the thin film, which is no more than 6.7% and is essentially zero at most frequencies. This proves that the shielding effectiveness of the thin film against terahertz waves mainly comes from the absorption of the material, with negligible reflection.

[0055] Figure 6(a) shows the overall shielding effectiveness of polyvinyl alcohol composite films containing molybdenum diselenide-coated WO3 nanosheets with different proportions of 1T-MoSe2 in the range of 0.2-1.8THz. Among them, the shielding effectiveness of (MoSe2-3 / WO3) / PVA film can reach 55.3dB at 1.55THz, the shielding effectiveness of (MoSe2-2 / WO3) / PVA film can reach 71.48dB at 1.65THz, and the shielding effectiveness of (MoSe2-1 / WO3) / PVA film can reach 46.3dB at 1.27THz. Moreover, the effective shielding effectiveness (≥10dB) of these films can reach 100% in the test band. In contrast, the shielding effectiveness of (MoSe2-0 / WO3) / PVA film without the metallic phase can only reach 44dB at 1.67THz. Furthermore, WO3 plays an important role in absorption as an electron acceptor. The properties of MoSe2-0 / PVA polymer films in the absence of WO3 and 1T-MoSe2 are as follows: Figure 1 As shown in (d), the effective shielding efficiency in the 0.2-1.8THz band can only reach 88% (effective shielding efficiency ≥10dB), and the highest shielding efficiency at 1.67THz is only 36.5dB, proving that its performance drops significantly in the absence of WO3 and 1T-MoSe2.

[0056] Figure 6 (b) represents the average shielding effectiveness of each of the four types of films. The average shielding effectiveness of the (MoSe2-0 / WO3) / PVA film without 1T-MoSe2 is only 24.37dB, which is much lower than that of the composite film containing 1T-MoSe2 with molybdenum diselenide coated with tungsten trioxide. In particular, the average shielding effectiveness of the (MoSe2-2 / WO3) / PVA film can reach 43.04dB in the test band, which has excellent terahertz shielding performance with absorption as the main feature.

[0057] Therefore, the molybdenum diselenide-coated tungsten trioxide nanosheet composite material containing 1T-MoSe2 encapsulated in the polymer film, under terahertz wave radiation, causes the upper electrons of 1T-MoSe2 to periodically inject and release into the (001) surface of the tungsten trioxide nanosheet. Under small stimulation, lattice distortion is very easy to occur. Since the polarization frequency induced by atomic valence inversion cannot follow the change of high-frequency terahertz waves, this polarization relaxation phenomenon will greatly enhance the absorption and shielding of terahertz waves.

[0058] The above-described embodiments are merely preferred embodiments of the present invention, but the implementation of the present invention is not limited to the above-described embodiments. For example, various combinations of the schemes in embodiments 1 to 4, and any other changes, modifications, substitutions, or combinations made without departing from the spirit and principle of the present invention, should be considered equivalent replacements and are all within the protection scope of the present invention.

Claims

1. A polyvinyl alcohol composite film containing 1T-MoSe2 molybdenum diselenide coated with WO3 nanosheets, characterized in that, The composite film uses a composite material with a heterogeneous structure formed by attaching molybdenum diselenide containing 1T-MoSe2 onto WO3 nanosheets as a filler, and polyvinyl alcohol as a matrix, wherein 1T-MoSe2 is combined with the (001) crystal plane of WO3.

2. The composite film as described in claim 1, characterized in that, Molybdenum diselenide containing 1T-MoSe2 has a nanosheet structure with a diameter of 30-50 nm.

3. The composite film as described in claim 1, characterized in that, WO3 nanosheets are thin-layer nanosheets with a planar diameter of 1-3 µm.

4. The composite film as described in claim 1, characterized in that, The composite material contains 30-50% 1T-MoSe2 and 20% WO3 by mass.

5. The composite film as described in claim 1, characterized in that, The mass fraction of 1T-MoSe2 in this composite material is 40%.

6. A method for preparing a composite thin film as described in any one of claims 1-5, characterized in that, The steps are as follows: Step 1: Dissolve sodium molybdate dihydrate and selenium powder in deionized water and stir mechanically for 1 hour. Sonicate until the solution is uniformly dispersed and record it as solution A. Step 2: Add sodium borohydride in a molar ratio of 2 to 4 with sodium molybdate dihydrate to solution A, stir until homogeneous, transfer the solution to a high-pressure reactor, react at 200 °C for 16 h, wash and vacuum dry to obtain molybdenum diselenide nanosheets containing 1T-MoSe2. Step 3: Dissolve sodium tungstate dihydrate and sodium chloride in deionized water, adjust the pH of the solution, add the molybdenum diselenide nanosheets containing 1T-MoSe2 described in Step 2, stir evenly, transfer to a high-pressure reactor, and react at 180℃ for 24 h. Step 4: After the reaction is complete, the mixture is washed and vacuum dried to obtain a composite material containing 1T-MoSe2 molybdenum diselenide coated with WO3 nanosheets. Step 5: Place the composite material from Step 4 into a polyvinyl alcohol solution, stir until homogeneous, and then drop-cast the resulting mixed solution onto a smooth silicon wafer. Dry it in a vacuum environment at 35°C to form a film.

7. The application of a composite thin film as described in any one of claims 1-5 in terahertz wave absorption.

8. The application as described in claim 7, characterized in that, The composite film has a shielding effectiveness of ≥10dB in the range of 0.2-1.8 THz.

9. A terahertz absorbing material, characterized in that, It is formed from the composite film as described in any one of claims 1-5.

10. A terahertz absorber, characterized in that, It includes the composite film as described in any one of claims 1-5.

11. A stealth coating, characterized in that, It is formed by coating a substrate with a composite film as described in any one of claims 1-5.

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