Perylene crystal / tungsten sulfide heterojunction material, preparation method thereof and nonlinear photonic device

Abstract

The invention provides a perylene crystal / tungsten sulfide heterojunction material, a preparation method thereof and a nonlinear photonic device, the heterojunction material is composed of an organic semiconductor perylene crystal layer and an inorganic semiconductor tungsten sulfide layer, and the organic semiconductor perylene crystal layer and the inorganic semiconductor tungsten sulfide layer are combined through Van der Waals' force to form a surface-surface heterojunction structure. According to the structure, optical anisotropy and energy donor characteristics of perylene crystals are utilized, a WS2 layer second harmonic (SHG) signal is remarkably enhanced through dipole-dipole coupling, and the highest enhancement multiple can reach 650 times. Besides, the heterojunction material has excellent second harmonic performance and excellent light stability, and the preparation process of the heterojunction material is mild in condition and high in controllability. The heterojunction belongs to a novel material of the invention, and meanwhile, the huge application potential of the heterojunction in the nonlinear optical field is found for the first time, for example, the heterojunction can be applied to the fields of nonlinear optical frequency doubling chips, on-chip photon modulators, polarization programmable photonic devices and the like.

Description

Technical Field

[0001] This application belongs to the field of nonlinear optics technology, and particularly relates to a perylene crystal / tungsten sulfide heterojunction material, its preparation method, and a nonlinear photonic device. Background Technology

[0002] In recent years, two-dimensional organic-inorganic heterostructures have attracted widespread attention as a novel functional material platform. These heterostructures, by combining organic semiconductors with atomically thin inorganic materials, and through rational material selection and precise structural design, can leverage interfacial interactions while maintaining the excellent properties of each component material, thereby introducing new functional characteristics. Researchers such as Samorì et al. have reported an optically addressable memory based on WSe2 thin films (…). Adv. Ma (ter. 2020, 32, 1907903.) This study demonstrates that by functionalizing a photochromic binary diarylethene (DAE) mixture with the DAE, the energy level alignment can be tuned using the photoisomerization effect of DAE, thereby achieving precise control of charge trapping and significantly improving the conductivity of TMDCs. This research shows that by screening and chemically functionalizing organic molecules and adjusting the interfacial coupling between them and TMDCs, the performance of TMDC devices can be effectively optimized, opening up new avenues for device performance regulation.

[0003] In addition to advancements in linear optoelectronics, TMDCs have also demonstrated superior performance in second-order nonlinear optical responses. The nonlinear polarizability of TMDC materials in second-order optical processes such as second harmonic generation (SHG) far exceeds that of traditional nonlinear optical crystals. For example, the second-order nonlinear polarizability χ of monolayer WS2 is approximately 0.45 nm V. 1 ( ACS Na No. 2022,1 6, 13933–13941.) Compared to traditional nonlinear optical crystals (such as barium β-borate BBO), their nonlinear response exceeds two orders of magnitude (Nano Lett. 2013, 13, 3329–3333.). The high secondary polarizability and sub-nanometer thickness of TMDCs make them a potential platform for laser frequency conversion, terahertz technology, and quantum nonlinear effects (Nat. Phys. 2019, 15, 242–246.). However, the finite interaction length and lack of an effective phase-matching mechanism in TMDCs still limit the strength of light-matter interactions, hindering the realization of high-efficiency devices.

[0004] Currently, several methods have attempted to enhance the nonlinear response of TMDCs through external electric fields, doping, or strain, but the gains obtained by these methods are typically less than an order of magnitude (Nat. Photonics 2018, 12, 430–436.). For example, Seyler and colleagues showed that monolayer WSe2 exhibits approximately four times the second harmonic generation (SHG) gain under an external electric field, approaching an order of magnitude at low temperatures (Adv. Sci. 2023, 10, 2206830.)28. In contrast, photonic strategies, such as plasmonic nanocavities, waveguides, and superconducting materials, can theoretically provide electromagnetic enhancements of several orders of magnitude (Nat. Nanotechnol. 2015, 10, 407–411.). For example, Zhang et al. demonstrated a nearly five-order-of-magnitude enhancement of second-harmonic output in monolayer WS2 by introducing high-order multipole coupling in a highly crystalline silver metasurface (Laser Photonics Rev. 2025, 19, 2401850.). However, these methods typically rely on highly localized hotspot regions, making it difficult to achieve spatially uniform enhancement and integrate them in large-scale fabrication, thus limiting their application in large-area nonlinear photonic devices. Therefore, there is an urgent need to develop new enhancement strategies to avoid over-reliance on strong localized hotspots while providing repeatable, tunable, and scalable interface couplings. Summary of the Invention

[0005] This application is made in view of the above-mentioned issues, and its purpose is to provide an organic-inorganic hybrid structure that constructs a novel interfacial coupling structure between two-dimensional materials and organic molecules by combining the photosensitizer perylene (Pe) with monolayer WS2.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: The first aspect of this application provides a perylene crystal / tungsten sulfide heterojunction material, which utilizes a combination of Pe crystal and monolayer WS2 to form a second-order nonlinear optical heterojunction material.

[0007] In any embodiment, the molar ratio of the Pe crystal to the monolayer WS2 is 1:1.

[0008] In any embodiment, the Pe crystal is α-crystal type, forming an α-Pe / WS2 heterojunction.

[0009] In any embodiment, the Pe crystal in the second-order nonlinear optical heterojunction material is square.

[0010] The first aspect of this application provides a method for preparing a perylene crystal / tungsten sulfide heterojunction material, comprising the following steps: 1) Obtain Pe crystals; 2) Obtain a single-layer WS2; 3) Pe crystal and monolayer WS2 are transferred by dry method to form a heterojunction material.

[0011] In any embodiment, the dry transfer method for preparing the Pe / WS2 heterojunction involves transferring a monolayer of WS2 onto the surface of a pre-prepared Pe crystal.

[0012] In any embodiment, the Pe crystal is of α-type, and the α-type Pe crystal (α-Pe) is prepared by a low-temperature space-confined self-assembly method.

[0013] In any embodiment, the low-temperature spatially confined self-assembly method for preparing α-crystalline Pe crystals includes the following steps: A. Weigh the perylene solid powder, add solvent, and ultrasonically vibrate to dissolve it completely; B. After complete dissolution, use a pipette to transfer a small amount of perylene solution and slowly drop it onto a petri dish containing TBAB (tetrabutylammonium bromide) / water solution; C. After being placed in the refrigerator and left to stand for a period of time, yellow crystals precipitate on the surface of the water. D. Using a wet transfer method, the yellow crystals are transferred to a clean Si / SiO2 wafer to obtain the α-type Pe crystal.

[0014] In any embodiment, the preparation of α-crystalline Pe crystals by the low-temperature spatial confinement self-assembly method specifically includes the following steps: A. Weigh 0.5 mg of the perylene molecule powder using an electronic balance and place it in a 3 mL sample vial. Add 1 mL of solvent and sonicate at room temperature for 6-10 minutes to completely dissolve it. The solvent is chlorobenzene and the solution concentration is 0.5 mg / mL. B. Prepare a 1 mg / mL TBAB solution, accurately transfer 5 mL into a 50-60 nm petri dish using a pipette, and place it in the refrigerator at 2-3℃. C. Accurately measure 50 μL of the 0.5 mg / mL perylene / chlorobenzene stock solution from step A using a pipette, and then slowly drop it onto the surface of the TBAB / water solution in the petri dish that was refrigerated in step B, and let it stand. D. Place the Si / SiO2 substrate to be cleaned on a cleaning rack and place the cleaning rack into a chemically resistant beaker; add acetone, anhydrous ethanol and deionized water to the beaker in sequence as cleaning solvents, and clean in the order of acetone → ethanol → water; each step is ultrasonically treated for 5 minutes in an ultrasonic cleaner. E. After completing the three-step ultrasonic cleaning, the substrate is removed and dried with high-purity nitrogen to remove residual moisture, resulting in a clean, dust-free and flat Si / SiO2 substrate. F. In the crystal transfer step, the cleaned Si / SiO2 substrate is immersed in an aqueous solution containing floating perylene crystals, and the Si / SiO2 substrate is gently moved to be directly below the crystals. Then, the substrate is quickly taken out of the water. The Si / SiO2 substrate with crystals is placed on a hot table at about 40 °C to evaporate the residual water and obtain the α-type Pe crystal.

[0015] In any embodiment, the monolayer WS2 is prepared by mechanical exfoliation.

[0016] In any embodiment, the mechanical peeling method of the single-layer WS2 includes the following steps: A. High-purity bulk WS2 crystals are used as the parent material, and the dust and oxide layer on their surface are removed by blowing nitrogen and wiping with anhydrous ethanol. B. Apply high-cleanliness tape to the surface of the WS2 block and press lightly to ensure full contact; C. The polydimethylsiloxane (PDMS) film is uniformly pulled up along the direction parallel to the crystal plane, so that part of the WS2 thin layer is peeled off and transferred to the surface of the PDMS film. D. Repeatedly adhere and peel off the obtained thin-layer area to remove excess layers one by one until a WS2 sheet with a thickness close to that of a single layer is obtained.

[0017] In any implementation, the dry transfer includes the following steps: A. With the aid of an optical microscope, the PDMS film carrying a monolayer of WS2 is aligned with the Si / SiO2 substrate pre-deposited with Pe crystals so that the target areas of WS2 and Pe crystals overlap. B. At approximately 85°C, slowly lower the PDMS film and bring it into contact with the Pe crystal surface. Keep it stationary for about 8–10 minutes to allow the WS2 layer to fully bond with the Pe crystal through van der Waals forces. C. After the WS2 and Pe crystal have stabilized, slowly peel off the PDMS film to transfer the monolayer WS2 to the surface of the Pe crystal, thereby forming a Pe / WS2 heterojunction structure. D. Place the obtained heterojunction sample in an inert atmosphere to enhance the stability of interlayer bonding and remove residual stress at the interface.

[0018] A nonlinear photonic device, using Pe / WS2 heterojunction material or prepared by the above-mentioned Pe / WS2 heterojunction material or method, is used for second harmonic response.

[0019] In any embodiment, the device includes a nonlinear optical frequency multiplier chip, an on-chip photonic modulator, or a polarization-programmable photon.

[0020] The Pe / WS2 heterojunction material of the present invention has excellent stability and can be used directly without the need for doping and protective materials. In particular, it can be used directly in the water and oxygen environment of the air and has the advantages of high reusability.

[0021] Compared with the prior art, implementing the present invention has the following beneficial effects: 1. This invention prepares a Pe / WS2 heterojunction material for nonlinear optics. The heterojunction material consists of an organic semiconductor perylene crystal layer and an inorganic semiconductor tungsten sulfide layer, which are bonded together by van der Waals forces to form a face-to-face heterojunction structure. Pe acts as the electron donor component, and WS2 acts as the electron acceptor component to form an organic-inorganic heterojunction material. Currently, no other Pe / WS2 heterojunction materials have been reported to exhibit second-order nonlinear properties.

[0022] 2. This structure utilizes the optical anisotropy and energy donor properties of perylene crystals to significantly enhance the second harmonic (SHG) signal of the WS2 layer through dipole-dipole coupling, with an enhancement factor of up to 650 times. Furthermore, the heterojunction material possesses excellent second harmonic performance as well as excellent optical stability, and its fabrication process is mild and highly controllable.

[0023] 3. The Pe / WS2 heterojunction material prepared by the present invention can be obtained by spatial confinement self-assembly, mechanical exfoliation and dry transfer processes.

[0024] 4. The Pe / WS2 heterojunction material mentioned in this invention can remain stable in air (it can be stored in air for at least six months) while still maintaining high second harmonic performance. In addition, the obtained heterojunction material has excellent second harmonic performance (650 times better than pure monolayer WS2 material) and has the advantage of high reusability.

[0025] 5. The Pe / WS2 heterojunction material prepared by the present invention has excellent second harmonic performance, i) the second harmonic performance is improved by 650 times compared with pure monolayer WS2 material; ii) the improvement of second harmonic performance in the heterojunction is a uniform improvement over a large area rather than just an improvement in a certain hot spot. 6. The Pe / WS2 heterojunction material prepared by the present invention has excellent second harmonic performance, which is closely related to the polarization of the excitation light, specifically the difference caused by excitation along the a and b crystal axes of the Pe crystal.

[0026] 7. The Pe / WS2 heterojunction material of this invention exhibits excellent second harmonic performance. Furthermore, while possessing excellent SHG performance, the heterojunction material also exhibits excellent material stability, and its preparation conditions are mild, simple, and low-cost. This material is a novel invention, and its enormous application potential in the field of nonlinear optics has been discovered for the first time, particularly in areas such as nonlinear optical frequency doubling chips, on-chip photonic modulators, and polarization-programmable photonic devices. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process flow for preparing α-crystalline Pe crystals using the low-temperature space-confined self-assembly method of this application; Figure 2 Flowchart of mechanical exfoliation and dry transfer process for preparing monolayer WS2 and Pe / WS2 heterojunctions for this application; Figure 3 These are microscopic images of the α-Pe crystals prepared in this application, where a is an optical microscope image and b is a fluorescence microscope image; Figure 4 The fluorescence spectrum of the α-Pe crystal prepared in this application under steady state; Figure 5 The X-ray diffraction (XRD) pattern of the α-Pe crystal prepared in this application; Figure 6 The fluorescence spectrum of monolayer WS2 prepared in this application under the A exciton steady state; Figure 7 This is a schematic diagram of the optical device used for measuring second harmonic generation in the product of this application; Figure 8 This is the power-dependent second harmonic response diagram of the α-Pe / WS2 heterostructure of this application; Figure 9 The SHG spectra of the α-Pe crystal, 1L WS2, and α-Pe / WS2 heterostructure of this application under 800 nm excitation are shown. Figure 10 This application demonstrates the SHG enhancement effect in the α-Pe / WS2 heterostructure under different excitation wavelengths. Figure 11 The optical imaging of α-Pe / WS2 (yellow dashed box) and 1L WS2 (white dashed box) in this application has a corresponding spatially resolved SHG intensity map; Figure 12 This is a schematic diagram of the "sandwich-herringbone" stacked crystal structure of α-Pe crystals in this application; Figure 13 This is a cross-polarized optical microscope image of the α-Pe crystal of this application; Figure 14This is the polarization-dependent absorption spectrum of α-Pe single crystal in this application; Figure 15 This is the polarization-dependent SHG response diagram of the α-Pe / WS2 heterojunction material in this application; Figure 16 This is a test diagram showing the air SHG stability of the α-Pe / WS2 heterojunction material of this application. Detailed Implementation

[0028] The following detailed description, with appropriate reference to the accompanying drawings, discloses the perylene crystal / tungsten sulfide heterojunction material, its preparation method, and embodiments of nonlinear photonic devices of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0029] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0030] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0031] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0032] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0033] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0034] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0035] In one embodiment of this application, a heterojunction material formed by perylene (Pe) crystal and tungsten sulfide is proposed, wherein the second-order nonlinear optical heterojunction material is formed by combining Pe crystal with a single layer of WS2.

[0036] The choice of monolayer WS2 is based on two considerations for multilayer materials. First, the parity of the number of layers needs to be considered. Our research focuses on 2H-phase WS2, which exhibits a layer-number dependence, displaying SHG (Sequential Absorption Gathering) with an odd number of layers, while exhibiting SHG with an even number of layers due to symmetry (SHG formation requires symmetry breaking). Second, multilayer materials also exhibit reabsorption effects. Therefore, monolayer 2H-phase WS2 materials show the best SHG performance. In any embodiment, the molar ratio of the Pe crystal to the monolayer WS2 is 1:1.

[0037] In any embodiment, the Pe crystal is α-crystal type, forming an α-Pe / WS2 heterojunction.

[0038] The heterojunction is composed of Pe crystal and a single layer of WS2, wherein the Pe crystal used is of the α-type, thus forming an α-Pe / WS2 heterojunction.

[0039] In one embodiment of this application, a method for preparing a perylene crystal / tungsten sulfide heterojunction material is provided, comprising the following steps: 1) Obtain Pe crystals; 2) Obtain a single-layer WS2; 3) Pe crystal and monolayer WS2 are transferred by dry method to form a heterojunction material.

[0040] In some embodiments, the Pe crystal and monolayer WS2 are dry-transferred at a molar ratio of 1:1 to form the second-order nonlinear optical heterojunction material.

[0041] In any embodiment, the Pe crystal is of the α-crystal form.

[0042] In some embodiments, the low-temperature space-confined self-assembly method of the α-type Pe crystal includes the following steps: A. Weigh the perylene solid powder, add solvent, and ultrasonically vibrate to dissolve it completely; B. After complete dissolution, use a pipette to slowly drop a small amount of perylene solution onto a petri dish containing water. C. After being placed in the refrigerator and left to stand for a period of time, yellow crystals precipitate on the surface of the water. D. Using a wet transfer method, the yellow crystals are transferred to a clean Si / SiO2 wafer to obtain the α-type Pe crystal.

[0043] TBAB is a surfactant. Its addition helps the Pe solution to disperse better on the water surface, thereby facilitating better volatilization and crystallization.

[0044] In some embodiments, the low-temperature space-confined self-assembly method of the α-type Pe crystal includes the following steps: A. Weigh 0.5 mg of the perylene molecule powder using an electronic balance and place it in a 3 mL sample vial. Add 1 mL of solvent and sonicate at room temperature for 6-10 minutes to completely dissolve it. The solvent is chlorobenzene and the solution concentration is 0.5 mg / mL. B. Prepare a 1 mg / mL TBAB (tetrabutylammonium bromide) solution. Accurately transfer 5 mL of the solution into a 50-60 nm petri dish using a pipette and place it in the refrigerator at 2-3°C. C. Using a pipette, accurately measure 50 μL of the 0.5 mg / mL perylene / chlorobenzene stock solution from step A, and then slowly drop it onto the surface of the TBAB / water solution in the chilled petri dish from step B. Let it stand. Wait for the chlorobenzene solvent to completely evaporate; a two-dimensional layer of perylene crystals will be observed on the surface of the water solution. D. To preliminarily determine the crystal morphology and crystal form, a small portion of the crystals obtained in step C were transferred onto a glass slide and observed under an optical microscope. These crystals were mostly square plates with side lengths of approximately 25-50 μm. Under 365 nm ultraviolet light irradiation, the crystals exhibited orange-yellow fluorescence, thus preliminarily identifying the α-type Pe crystals. E. Place the Si / SiO2 substrate to be cleaned on the cleaning rack, and place the cleaning rack into a chemically resistant beaker; F. Add acetone, anhydrous ethanol and deionized water to the beaker in sequence as cleaning solvents, and clean in the order of acetone → ethanol → water; each step is ultrasonically treated for 5 minutes in an ultrasonic cleaner to remove organic contaminants, residual particles and oxidized impurities from the substrate surface. G. After completing the three-step ultrasonic cleaning, the substrate is removed and dried with high-purity nitrogen to remove residual moisture, resulting in a clean, dust-free and flat Si / SiO2 substrate. H. In the crystal transfer step, the cleaned Si / SiO2 substrate is immersed in an aqueous solution containing floating perylene crystals, and the Si / SiO2 substrate is gently moved to be directly below the crystals. Then, the substrate is quickly removed from the water. The Si / SiO2 substrate with crystals is placed on a hot plate at about 40 °C to evaporate any remaining moisture.

[0045] In some embodiments, the mechanical peeling method of the single-layer WS2 includes the following steps: A. High-purity bulk WS2 crystals are used as the parent material, and the dust and oxide layer on their surface are removed by blowing nitrogen and wiping with anhydrous ethanol. B. Apply high-cleanliness tape to the surface of the WS2 block and press lightly to ensure full contact; C. The polydimethylsiloxane (PDMS) film is uniformly pulled up along the direction parallel to the crystal plane, so that part of the WS2 thin layer is peeled off and transferred to the surface of the PDMS film. D. Repeatedly adhere and peel off the obtained thin-layer area to remove excess layers one by one until a WS2 sheet with a thickness close to that of a single layer is obtained.

[0046] E. The WS2 sheet was placed in a micro-photoluminescence (Micro-PL) testing system and a 532 nm continuous laser was used as the excitation source for spectral testing. The test results showed a strong exciton emission peak at 615 nm, which is consistent with the characteristic peak of A exciton emission of monolayer WS2. Based on this, it was confirmed that the WS2 sheet is a monolayer material.

[0047] In some embodiments, the dry transfer of the Pe crystal to the monolayer WS2 heterojunction includes the following steps: A. With the aid of an optical microscope, the PDMS film carrying a monolayer of WS2 is aligned with the Si / SiO2 substrate pre-deposited with Pe crystals so that the target areas of WS2 and Pe crystals overlap. B. At approximately 85°C, slowly lower the PDMS film and bring it into contact with the Pe crystal surface. Keep it stationary for about 8–10 minutes to allow the WS2 layer to fully bond with the Pe crystal through van der Waals forces. C. After the WS2 and Pe crystal have stabilized, slowly peel off the PDMS film to transfer the monolayer WS2 to the surface of the Pe crystal, thereby forming a Pe / WS2 heterojunction structure. D. Place the obtained heterojunction sample in an inert atmosphere to enhance the stability of interlayer bonding and remove residual stress at the interface. In one embodiment of this application, a nonlinear photonic device is proposed, which uses the Pe / WS2 heterojunction material or method described above to prepare a Pe / WS2 heterojunction material for second harmonic response.

[0048] In some embodiments, the device includes a nonlinear optical frequency multiplier chip, an on-chip photonic modulator, or a polarization-programmable photon.

[0049] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0050] Example 1 like Figure 1 As shown in this embodiment, the low-temperature spatial confinement self-assembly process route for preparing α-phase perylene crystal materials is detailed as follows: The preparation method of α-pe crystal (α-Pe), a low-temperature space-confined self-assembly method, includes the following steps: (1) Weigh 0.5 mg of the perylene molecule powder using an electronic balance and place it in a 3 mL sample bottle. Add 1 mL of solvent and sonicate at room temperature for 6-10 minutes to completely dissolve it. The solvent is chlorobenzene and the solution concentration is 0.5 mg / mL.

[0051] (2) Prepare a 1 mg / mL TBAB (tetrabutylammonium bromide) solution. Accurately transfer 5 mL of the solution into a 50-60 nm petri dish using a pipette and place it in the refrigerator at 2-3°C.

[0052] (3) Accurately measure 50 μL of the 0.5 mg / mL perylene / chlorobenzene stock solution from step A using a pipette, and then slowly drop it onto the surface of the TBAB / water solution in the petri dish that was chilled in step (2), and let it stand. Wait for the chlorobenzene solvent to completely evaporate, and a layer of two-dimensional perylene crystals will be observed on the surface of the water solution.

[0053] (4) To preliminarily determine the crystal morphology and crystal form, the crystals obtained in step C were placed on a glass slide and observed under an optical microscope. Most of these crystals were square plates with a side length of about 25-50 μm. Under 365 nm ultraviolet light, the crystals showed orange-yellow fluorescence, which could preliminarily determine the α crystal form of Pe crystals.

[0054] (5) Place the Si / SiO2 substrate to be cleaned on the cleaning rack and place the cleaning rack in a chemically resistant beaker. (6) Add acetone, anhydrous ethanol and deionized water to the beaker in sequence as cleaning solvents, and clean in the order of acetone → ethanol → water; each step is ultrasonically treated for 5 minutes in an ultrasonic cleaner to remove organic pollutants, residual particles and oxidized impurities from the substrate surface.

[0055] (7) After completing the three-step ultrasonic cleaning, the substrate is removed and dried with high-purity nitrogen to remove residual moisture, so as to obtain a clean, dust-free and flat Si / SiO2 substrate.

[0056] (8) In the crystal transfer step, the cleaned Si / SiO2 substrate is immersed in an aqueous solution containing floating perylene crystals, and the Si / SiO2 substrate is gently moved to be directly below the crystals. Then, the substrate is quickly removed from the water. The Si / SiO2 substrate with crystals is placed on a hot plate at about 40 °C to evaporate the residual water.

[0057] Example 2 like Figure 2 As shown, this embodiment uses mechanical exfoliation and dry transfer to prepare monolayer WS2 and Pe / WS2 heterojunction materials, respectively. The detailed steps of mechanical exfoliation and dry transfer are as follows: (1) High-purity bulk WS2 crystals are used as the parent material, and the dust and oxide layer on their surface are removed by blowing nitrogen and wiping with anhydrous ethanol.

[0058] (2) Apply high-cleanliness tape to the surface of the WS2 block and press it lightly to ensure full contact.

[0059] (3) Pull up the polydimethylsiloxane (PDMS) film evenly along the direction parallel to the crystal plane so that part of the WS2 thin layer is peeled off and transferred to the PDMS film surface.

[0060] (4) Repeatedly stick and peel off the obtained thin layer area to remove the excess layers one by one until a single-layer WS2 sheet is obtained.

[0061] (5) With the aid of an optical microscope, the PDMS film carrying a single layer of WS2 is aligned with the Si / SiO2 substrate with pre-deposited Pe crystals so that the target area of ​​WS2 and Pe crystals overlaps.

[0062] (6) At approximately 85°C, slowly lower the PDMS film and bring it into contact with the Pe crystal surface. Keep it stationary for approximately 8–10 minutes to allow the WS2 layer to fully bond with the Pe crystal through van der Waals forces.

[0063] (7) After the WS2 and Pe crystal are stable, slowly peel off the PDMS film to transfer the monolayer WS2 to the surface of the Pe crystal, thereby forming a Pe / WS2 heterojunction structure.

[0064] (8) The obtained heterojunction sample was placed in an inert atmosphere to enhance the interlayer bonding stability and remove residual stress at the interface.

[0065] Example 1 To confirm that the crystal obtained in Example 1 was an α-phase perylene (α-Pe) crystal, imaging under a fluorescence optical microscope, fluorescence spectroscopy, and X-ray diffraction were performed. The results are as follows: Figure 3 , Figure 4 , Figure 5 As shown.

[0066] from Figure 3 As can be seen, Example 1 yielded square, plate-like crystals approximately 20 μm in size, which were observed under a fluorescence microscope. Figure 3 As shown in b, the entire square crystal exhibits yellow fluorescence. Steady-state fluorescence spectroscopy of the α-Pe crystal prepared in Example 1 was performed at room temperature using excitation light at a wavelength of 405 nm, and the results are as follows. Figure 4 As shown, Pe crystals exhibit significant fluorescence emission in the visible light region, with the emission band primarily distributed around 570-600 nm. This result indicates that Pe crystals can produce strong and broadband visible light fluorescence emission under 405 nm excitation. Furthermore, from... Figure 5It can be seen that the prepared α-phase Pe crystal has sharp and clear X-ray diffraction peaks at 2θ = 8.73°, 17.55°, and 26.47°, indicating that the material is a long-range ordered, anisotropic crystal with good crystallinity. Furthermore, these diffraction peaks are highly consistent with the (001) plane diffraction peaks of α-Pe, with an interlayer spacing of 10.109 Å. In addition, the sharpness and strong intensity of the diffraction peaks and the flat baseline further confirm that the synthesized two-dimensional organic crystal is an α-type Pe crystal and possesses high-quality crystallinity.

[0067] Example 2 Photoluminescence spectra of the monolayer WS2 prepared in Example 2 were obtained, and the results are as follows: Figure 6 As shown, the WS2 sheet was placed in a commercial HORIBA XploRA Raman spectrometer testing system, and a 532 nm continuous laser was used as the excitation source for spectral testing. The test results showed a strong exciton emission peak at 615 nm, which is consistent with the characteristic peak of A exciton emission of monolayer WS2. Based on this, it was confirmed that the WS2 sheet is a monolayer material.

[0068] Example 3 To investigate the second harmonic performance of the Pe / WS2 heterojunction prepared in Example 2, a second harmonic testing system was built, as follows: Figure 7 As shown.

[0069] Figure 7The apparatus used to measure the second harmonic generation (SHG) response performance of Pe / WS2 heterojunction samples was demonstrated. The testing system mainly consists of a laser excitation module, an optical control unit, a sample testing unit, and a signal acquisition unit. The excitation source is a Ti:Sapphire femtosecond laser with a pulse repetition frequency of 80 MHz, an output wavelength of 800 nm, and a pulse width of approximately 140 fs. After the laser beam's polarization direction is adjusted by a polarizer, stray light signals are filtered out by a long-pass filter, and the incident polarization angle is controlled by a half-wave plate. After reflection by a beamsplitter, the laser beam is focused by an objective lens onto the sample surface to form a spot of approximately 1 μm, used to excite the sample's second harmonic signal. The sample is a Pe / WS2 heterojunction placed on a Si / SiO2 substrate, and its testing area is positioned using a precision displacement platform. The excitation light irradiates the sample in a normal incident manner, and the generated second harmonic signal (400 nm, 2ω) is collected by the objective lens and then passed through a short-pass filter to remove residual signals from the excitation light. After the polarization state is adjusted by the analyzer, the signal is introduced into the spectrometer for signal detection and recording.

[0070] Example of effect 4 The second harmonic generation (SHG) performance of the monolayer WS2, Pe, and Pe / WS2 heterojunctions prepared in Examples 1 and 2 was investigated, and the results are as follows: Figure 8 ,like Figure 9 As shown.

[0071] First, to determine whether the 400 nm response observed in the Pe / WS2 heterojunction under 800 nm femtosecond laser excitation is attributable to its SHG response, a variable-power SHG response test was performed on the Pe / WS2 heterojunction. The results are as follows: Figure 8 As shown. Figure 8 Figure a shows that the SHG response of the material also increases exponentially with increasing excitation power. Through... Figure 8 As shown in b, by fitting the relationship between the pump power light intensity and the intensity of the SHG material, it can be seen that the excitation power has a square relationship with the SHG intensity, thus verifying that the signal originates from a typical second-order nonlinear process. Secondly, the performance of the SHG in the Pe / WS2 heterojunction is investigated, such as... Figure 9As shown, under 800 nm femtosecond pulsed laser excitation, the SHG (Spiritual Growth Governance) behavior of pure monolayer WS2, Pe crystal, and their heterojunction was compared. The Pe crystal itself did not exhibit a detectable SHG signal, thus ruling out the hypothesis that the SHG enhancement signal originated from the superposition of the Pe crystal and WS2. Excitingly, compared to pure WS2, the SHG intensity was significantly improved after WS2 and Pe crystal were combined into a heterojunction. This result eliminates the possibility that the enhancement effect originates from the intrinsic nonlinear response of the organic component.

[0072] Example 5 The enhancement of second harmonic generation (SHG) was investigated under different excitation bands for the α-Pe / WS2 heterojunctions prepared in Examples 1 and 2. The results are as follows: Figure 10 As shown.

[0073] Figure 10 a shows the SHG spectra of monolayer WS2 at different excitation wavelengths. It can be observed that as the excitation wavelength increases from 750 nm to 900 nm, the SHG emission peak position shifts linearly, ending at half the excitation wavelength, consistent with typical second-order nonlinear process characteristics. The SHG peak intensity changes little under different excitation wavelengths, and the overall signal is weak, indicating that the second-order nonlinear response of monolayer WS2 is limited under conditions far from resonance. Figure 10 b shows the SHG spectrum of the Pe / WS2 heterojunction within the same wavelength range. Compared to monolayer WS2, the Pe / WS2 heterojunction exhibits significantly enhanced SHG intensity across the entire wavelength range, reaching a peak at 800 nm excitation, representing an increase of approximately two orders of magnitude in SHG signal intensity. With further increases in excitation wavelength, the SHG intensity gradually decreases. This trend indicates that the SHG response of the Pe / WS2 heterojunction exhibits a clear excitation wavelength dependence. Figure 10 c shows the relationship between the SHG enhancement factor of the Pe / WS2 heterojunction and the pure WS2 sample as a function of excitation wavelength. It can be seen that SHG enhancement is significant in the 750–900 nm range, with the maximum enhancement occurring at 800 nm, representing an enhancement factor of approximately 650 times. Above 830 nm, the enhancement effect rapidly weakens, indicating that SHG enhancement is closely related to specific optical resonance conditions.

[0074] Example 6 Three-dimensional imaging of the Pe / WS2 heterojunctions prepared in Examples 1 and 2 was performed on the single-layer WS2, Pe, and second harmonic. The results are as follows: Figure 11 As shown.

[0075] like Figure 11The image shows the spatial distribution test results of second harmonic generation (SHG) in the Pe / WS2 heterojunction sample in this embodiment of the invention. An SHG mapping system based on a scanning nonlinear optical microscope was used, with an excitation wavelength of 800 nm and a wavelength of 1.1 × 10⁻⁶ nm. 14 W / m 2 At power density, surface scan tests were performed on samples that simultaneously contained pure monolayer WS2 regions and α-Pe / WS2 heterojunction regions. Figure 11 The left image is an optical microscope image of the sample, where the lower blue-purple area is a single layer of WS2, and the upper light yellow area is a Pe / WS2 heterojunction formed by Pe crystal coverage; Figure 11 The right figure shows the spatial distribution of SHG intensity, with color intensity representing SHG signal strength (Counts / s). It is clearly observed from the figure that the SHG signal intensity in the α-Pe / WS2 heterojunction region is significantly higher than that in the exposed monolayer WS2 region, with the former's signal intensity mainly distributed around 10. 3 -10 4 The latter only has counts / s, while the former is only in the range of 10–100 counts / s. This result shows that by introducing Pe crystals on the WS2 surface to form an organic-inorganic interface, the second-order nonlinear optical response of the material can be significantly enhanced. Notably, the SHG signal distribution in the Pe / WS2 heterojunction region is uniform and continuous, without obvious local hotspots or signal abrupt changes, indicating that the enhancement effect originates from the uniform interface coupling between the organic molecules and WS2, rather than a hotspot enhancement mechanism induced by localized plasmons or defects. This characteristic demonstrates that the organic-inorganic heterojunction system constructed in this invention can achieve a large-area, controllable, and highly repeatable second-order harmonic enhancement effect. The uniform second-order nonlinear enhancement achieved by this invention through interface engineering provides a new technical approach for the construction and device application of efficient two-dimensional nonlinear optical materials.

[0076] Example 7 The α-Pe crystal obtained in Example 1 was characterized by single-crystal XRD, polarized light microscopy, and polarized absorption spectroscopy to determine the a and b crystal axes. The results are as follows: Figure 12 , Figure 13 , Figure 14 As shown.

[0077] First, the α-Pe crystal was characterized by single-crystal XRD to determine its specific stacking arrangement. The results are as follows: Figure 12 As shown, α-Pe crystals exhibit a "sandwich-herringbone" stacking, in which π-π dimers are arranged along the a-axis and dimers are alternately arranged along the b-axis.

[0078] Secondly, the a-axis or b-axis of the crystal is first determined using a cross-polarized microscope, such as... Figure 13As shown. When performing orthogonal polarized light microscopy on α-Pe single crystals, the polarization direction of the analyzer is fixed, and the crystal axis orientation in the plane is determined by rotating the polarizer. For example... Figure 13 As shown in Figure a, when the polarization direction of the polarizer is at a certain angle relative to the geometric edge of the crystal, the crystal region exhibits a uniform bright color without significant extinction. Continuing to rotate the polarizer, when the polarization direction is parallel or perpendicular to one of the geometric edges of the crystal, as shown in Figure a... Figure 13 As shown in b, the crystal exhibits an overall dark field, displaying a typical extinction state. Under orthogonal polarization conditions, the crystal only undergoes complete extinction when its principal optical refraction axis is parallel or perpendicular to the direction of polarized light. Therefore, the edge direction corresponding to the complete extinction of the crystal can be determined as the crystal axis a or b direction of the α-Pe single crystal in that plane.

[0079] Finally, after determining the specific crystal axis position, by changing the relationship between the incident polarization and the crystal axis, and measuring the absorption spectrum of the α-Pe crystal at this time, the specific directions of the a and b crystal axes of the α-Pe crystal can be determined. The results are as follows: Figure 14 As shown, the polarization-resolved absorption spectra of α-Pe were measured using incident light polarization along the b-axis (0°), 45° between the a-axis and b-axis, and the a-axis (90°). When the polarization direction is parallel to the b-axis, the absorption feature near 477 nm is enhanced, corresponding to low-energy exciton transitions dominated by alternating dimer orientations. The significant anisotropy reflects the distinct transition dipole strengths associated with the a and b crystal axes, consistent with the "sandwich-chevron" molecular packing of α-Pe.

[0080] Example 8 The Pe / WS2 heterojunctions prepared in Examples 1 and 2 were subjected to polarization-variable SHG tests to demonstrate the modulation of the SHG response of the heterojunction on the a and b axes of the crystal. Figure 15 As shown.

[0081] In this embodiment, polarization-resolved second harmonic generation (SHG) tests were performed on the Pe / WS2 heterojunction to characterize its anisotropic nonlinear optical response along the a-axis and b-axis of the crystal. During the test, under fixed excitation wavelength and power conditions, linearly polarized incident light was used. The incident polarization was continuously varied from 0° to 360° relative to the crystallographic orientation by rotating the polarizer, and the corresponding SHG intensities were recorded. Figure 15As shown, the SHG intensity exhibits a distinct 180° periodic variation with the polarization angle: when the polarization angle is 0° and 180°, corresponding to the incident polarization direction being parallel to the crystal b-axis of the Pe / WS2 heterojunction, the SHG signal is significantly weakened, approaching its minimum value; when the polarization angle is 90° and 270°, corresponding to the incident polarization direction being parallel to the crystal a-axis, the SHG intensity reaches its peak, reaching approximately 5.8 × 10⁻⁶. 4 Counts / s. This demonstrates that the Pe / WS2 heterojunction exhibits a significantly enhanced second-order nonlinear response along the a-axis, while significantly suppressed along the b-axis, achieving effective control of the SHG output intensity along the crystal's a and b axes. This provides a basis for the application of this heterojunction in polarization-tunable nonlinear optical devices.

[0082] Example 9 The changes in the SHG response of the Pe / WS2 heterojunctions prepared in Examples 1 and 2 before and after exposure to air for six months are compared, as follows: Figure 16 As shown.

[0083] from Figure 16 As can be seen from the comparison of the SHG responses of the Pe / WS2 heterojunction samples prepared in Examples 1 and 2 before and after six months of exposure to air, their long-term stability can be observed. During the testing process, the excitation conditions (1mW, 800 nm femtosecond laser) were kept consistent, and to reduce the randomness of the test results, the SHG spectrum at each time point was measured three times under the same conditions, and the average value was taken as the final data. The results show that the SHG peak position of the newly prepared sample is stably distributed at 400 nm, and the peak intensity is approximately 5.9 × 10⁻⁶. 4 The sample was placed in room temperature air for six months, and the same SHG test was performed again. The SHG peak position and intensity remained essentially unchanged, with no significant shift in peak position and extremely limited signal intensity attenuation. These results demonstrate that the Pe / WS2 heterojunction prepared in this invention exhibits excellent optical stability under normal air conditions, and its second-order nonlinear response maintains high consistency even under long-term exposure conditions, providing experimental evidence for the long-term reliable use of heterojunctions in practical optical devices.

[0084] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A perylene crystal / tungsten sulfide heterojunction material, characterized in that, A second-order nonlinear optical heterojunction material is formed by combining Pe crystal with a single layer of WS2.

2. The perylene crystal / tungsten sulfide heterojunction material according to claim 1, characterized in that, The molar ratio of the Pe crystal to the monolayer WS2 is 1:1; the Pe crystal is α-crystal type, forming an α-Pe / WS2 heterojunction.

3. A method for preparing perylene crystal / tungsten sulfide heterojunction materials, comprising the following steps: 1) Obtain Pe crystals; 2) Obtain a single-layer WS2; 3) Pe crystal and monolayer WS2 are transferred by dry method to form a heterojunction material.

4. The method for preparing perylene crystal / tungsten sulfide heterojunction material according to claim 3, characterized in that, The Pe crystal is of the α-type, and the α-type Pe crystal (α-Pe) is prepared by a low-temperature space-confined self-assembly method.

5. The method for preparing perylene crystal / tungsten sulfide heterojunction material according to claim 3, characterized in that, The preparation of α-crystalline Pe crystals by the low-temperature space-confined self-assembly method includes the following steps: A. Weigh the perylene solid powder, add solvent, and ultrasonically vibrate to dissolve it completely; B. After complete dissolution, use a pipette to slowly drop a small amount of perylene solution onto a petri dish containing water. C. After being placed in the refrigerator and left to stand for a period of time, yellow crystals precipitate on the surface of the water. D. Using a wet transfer method, the yellow crystals are transferred to a clean Si / SiO2 wafer to obtain the α-type Pe crystal.

6. The method for preparing perylene crystal / tungsten sulfide heterojunction material according to claim 3, characterized in that, The single-layer WS2 was prepared by mechanical exfoliation.

7. The method for preparing perylene crystal / tungsten sulfide heterojunction material according to claim 3 or 6, characterized in that, The mechanical peeling method for the single-layer WS2 includes the following steps: A. High-purity bulk WS2 crystals are used as the parent material, and the dust and oxide layer on their surface are removed by blowing nitrogen and wiping with anhydrous ethanol. B. Apply high-cleanliness tape to the surface of the WS2 block and press lightly to ensure full contact; C. The polydimethylsiloxane (PDMS) film is uniformly pulled up along the direction parallel to the crystal plane, so that part of the WS2 thin layer is peeled off and transferred to the surface of the PDMS film. D. Repeatedly adhere and peel off the obtained thin-layer area to remove excess layers one by one until a WS2 sheet with a thickness close to that of a single layer is obtained.

8. The method for preparing perylene crystal / tungsten sulfide heterojunction material according to claim 3, characterized in that, The dry transfer process includes the following steps: A. With the aid of an optical microscope, the PDMS film carrying a monolayer of WS2 is aligned with the Si / SiO2 substrate pre-deposited with Pe crystals so that the target areas of WS2 and Pe crystals overlap. B. At approximately 85°C, slowly lower the PDMS film and bring it into contact with the Pe crystal surface. Keep it stationary for about 8–10 minutes to allow the WS2 layer to fully bond with the Pe crystal through van der Waals forces. C. After the WS2 and Pe crystal have stabilized, slowly peel off the PDMS film to transfer the monolayer WS2 to the surface of the Pe crystal, thereby forming a Pe / WS2 heterojunction structure. D. Place the obtained heterojunction sample in an inert atmosphere to enhance the stability of interlayer bonding and remove residual stress at the interface.

9. A nonlinear photonic device, using the Pe / WS2 heterojunction material according to any one of claims 1 to 3 or the Pe / WS2 heterojunction material prepared by the manufacturing method of the Pe / WS2 heterojunction material according to any one of claims 4 to 8, for second harmonic response.

10. The nonlinear photonic device according to claim 9, characterized in that, The device includes a nonlinear optical frequency multiplier chip, an on-chip photonic modulator, or a polarization-programmable photon.

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