Three-dimensional crystal, construction method thereof and optical element

Abstract

The invention discloses a three-dimensional crystal, a construction method thereof and an optical element, and belongs to the technical field of semiconductor material preparation. The construction method of the three-dimensional crystal comprises the following steps: S101, providing a two-dimensional material primitive structure with m layers; s102, the two-dimensional material element structure is cut into a first part and a second part; s103, the first part and the second part are stacked, so that the number of layers of the two-dimensional material element structure is doubled; and S104, the step S102 and the step S103 are repeated at least once, the three-dimensional crystal with the layer number of m * 2N is formed through N times of stacking operation, and m and N are positive integers larger than or equal to 1. According to the three-dimensional crystal, the construction method of the three-dimensional crystal and the optical element provided by the invention, the two-dimensional material element structure is cut and stacked by utilizing the physical characteristics of the two-dimensional material element structure, so that the number of layers is increased exponentially in limited operation steps.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor material preparation, and in particular relates to a three-dimensional crystal and a construction method thereof, and an optical element. Background Art

[0002] Two-dimensional materials have broad application potential in electronics, optoelectronics, energy storage and other fields due to their unique layered structure and excellent optoelectronic properties. Among them, transition metal dichalcogenides (TMDCs) are the most representative type of two-dimensional semiconductor materials. They have become a hot topic of research in recent years due to their tunable band structure and strong layer-dependent optical properties. The light-matter interaction of single-layer materials is very limited, and there is an urgent need to inherit and develop the excellent optical properties of single-layer materials in three-dimensional crystals. However, traditional two-dimensional material stacking or synthesis methods still face many challenges in constructing multilayered crystals.

[0003] The common methods for constructing layered crystals currently include chemical vapor deposition (CVD). The CVD method can be used to prepare single-layer or multi-layer TMDCs materials on a large scale and is suitable for the growth of homogeneous layered crystals. However, due to the limitations of growth dynamics, after a certain number of layers, the interlayer coupling effect is significantly enhanced, resulting in the energy band changing from direct band gap to indirect band gap, which in turn significantly reduces the photoluminescence (PL) efficiency. For example, studies have shown that more than 17 layers of 3R phase MoS can be grown using the CVD method. 2 , but as the number of layers increases, the fluorescence emission intensity decreases significantly. This phenomenon is mainly attributed to the change in electronic structure caused by the enhancement of interlayer coupling. In addition, the CVD method is usually difficult to control the interlayer stacking angle and coupling state as needed, which is extremely limited for the construction of heterogeneous layered crystals.

[0004] Therefore, it is necessary to provide a new solution to the above technical problems. Summary of the invention

[0005] The purpose of the present invention is to provide a three-dimensional crystal and its construction method and optical element, which can realize the accurate, efficient and high-degree-of-freedom construction of crystals and realize the exponential growth of the number of crystal layers.

[0006] To achieve the above purpose, the technical solution provided by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for constructing a three-dimensional crystal, comprising the following steps:

[0008] S101: providing a two-dimensional material elementary structure having m layers;

[0009] S102: cutting the two-dimensional material elementary structure into a first part and a second part;

[0010] S103: stacking the first part and the second part to double the number of layers of the two-dimensional material elementary structure;

[0011] S104: Repeat steps S102 and S103 at least once, and form m×2 layers through N stacking operations. N A three-dimensional crystal of layers, wherein m and N are positive integers greater than or equal to 1.

[0012] In one or more embodiments, step S101 specifically includes: transferring the two-dimensional material elementary structure obtained by physical vapor deposition, chemical vapor deposition or stripping method to a flexible polymer.

[0013] In one or more embodiments, step S102 specifically includes: making a part of the two-dimensional material element structure on the flexible polymer adhere to the substrate, and keeping the other part suspended; applying force to the two-dimensional material element structure along the edge of the substrate to cut the two-dimensional material element structure into a first part and a second part, wherein the first part is adhered to the substrate and the second part is adhered to the flexible polymer.

[0014] In one or more embodiments, the bonding force between the two-dimensional material unit structure and the substrate is greater than the bonding force between the two-dimensional material unit structure and the flexible polymer.

[0015] In one or more embodiments, the flexible polymer is PDMS, PMMA, PPC, PVA, PI or PET film, the substrate includes a substrate layer and a sacrificial layer formed on the surface of the substrate layer, and the material of the substrate layer is SiO 2 / Si, gold, sapphire, quartz or boron nitride, and the material of the sacrificial layer is nickel, iron, copper, aluminum, zinc, titanium, molybdenum or chromium.

[0016] In one or more embodiments, step S103 specifically includes: moving the flexible polymer so that the second part attached to the flexible polymer is stacked with the first part attached to the substrate to obtain a two-dimensional material elementary structure with doubled number of layers.

[0017] In one or more embodiments, the construction method also includes: placing the stacked structure comprising a flexible polymer, a two-dimensional material elementary structure and a substrate in a chemical solution, dissolving the bonding interface between the substrate and the two-dimensional material elementary structure, separating the substrate from the two-dimensional material elementary structure, and transferring the two-dimensional material elementary structure to the flexible polymer.

[0018] In one or more embodiments, the two-dimensional material elementary structure is a single-layer two-dimensional material or a multi-layer heterogeneous two-dimensional material, and the material of the two-dimensional material elementary structure is transition metal chalcogenide, graphene or hexagonal boron nitride.

[0019] In a second aspect, the present invention provides a three-dimensional crystal, which is constructed by the aforementioned construction method, and each layer of material of the three-dimensional crystal is coupled by van der Waals force.

[0020] In a third aspect, the present invention provides an optical element comprising the aforementioned three-dimensional crystal.

[0021] Compared with the prior art, the three-dimensional crystal, its construction method, and optical element provided by the present invention cut the two-dimensional material elementary structure and stack it using its own physical properties, so that the number of layers increases exponentially within a limited number of operation steps; this method can not only reduce the number of operations required for the traditional layer-by-layer stacking method and improve the preparation efficiency, but also ensure that all layers are derived from the same parent material, avoiding the lattice mismatch problem that may occur when materials from different sources are stacked, and realizing the replication of the interface coupling state during the increase of the number of layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 is a flow chart of a method for constructing a three-dimensional crystal in one embodiment of the present invention;

[0024] Figure 2 A schematic diagram of the operation of a method for constructing a three-dimensional crystal in one embodiment of the present invention;

[0025] Figure 3 The centimeter-scale CVD-grown single crystal MoS 2 Optical image of

[0026] Figure 4 The 16-layer stepped MoS in Example 1 2 Optical images of crystals;

[0027] Figure 5 The 16-layer stepped MoS in Example 1 2 Schematic diagram of the crystal structure;

[0028] Figure 6 The 16-layer stepped MoS with different number of layers in Example 1 2 Photoluminescence spectrum of the crystal;

[0029] Figure 7 The 16-layer stepped MoS in Example 1 2Crystal and 2H phase MoS 2 Comparison of the photoluminescence properties of the crystals;

[0030] Figure 8 The 16-layer stepped MoS in Example 1 2 Crystal and 2H phase MoS 2 Optical microscopic image of the crystal and imaging of the integrated fluorescence intensity of A exciton;

[0031] Fig. 9 The 16-layer stepped MoS in Example 1 2 Crystal and 2H phase MoS 2 The dependence of the integrated fluorescence intensity of the crystal at the A exciton energy on the number of layers;

[0032] Fig.10 The 16-layer stepped MoS in Example 1 2 Crystal and 2H phase MoS 2 A graph showing the dependence of the relative fluorescence quantum yield of the crystal on the number of layers;

[0033] Fig.11 For the double-layer WSe in Example 2 2 / MoS 2 Optical images of heterogeneous superlattices;

[0034] Fig.12 For the 8-layer WSe in Example 2 2 / (MoS 2 / WSe 2 ) 3 / MoS 2 Optical images of superlattices;

[0035] Fig.13 For the 8-layer WSe in Example 2 2 / (MoS 2 / WSe 2 ) 3 / MoS 2 Schematic diagram of the superlattice structure;

[0036] Fig.14 For the 8-layer WSe in Example 2 2 / (MoS 2 / WSe 2 ) 3 / MoS 2 Schematic diagram of exciton species in heterogeneous superlattice;

[0037] Fig.15 For the 8-layer WSe in Example 2 2 / (MoS 2 / WSe 2 ) 3 / MoS 2 Heterogeneous superlattice and double-layer WSe 2 / MoS 2 Near-infrared fluorescence spectrum of the heterojunction. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0039] Unless otherwise indicated, all numbers used in the specification and claims to represent feature sizes, quantities and physical properties should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise indicated, the numerical parameters listed in the above specification and the attached claims are approximate values, and those skilled in the art can use the teachings disclosed herein to seek to obtain the desired properties and appropriately change these approximate values. The use of numerical ranges expressed as endpoints includes all numbers within the range and any range within the range, for example, 1 to 5 includes 1, 1.2, 1.4, 1.55, 2, 2.75, 3, 3.80, 4 and 5, etc.

[0040] In recent years, with the widespread application of two-dimensional materials in optoelectronics, quantum computing, and nanoelectronics, the construction of multilayered crystals has become a research hotspot. Two-dimensional materials such as transition metal dichalcogenides (TMDCs) exhibit different physical properties when the number of layers changes due to their unique electronic structure. However, the traditional multilayer stacking method still has many challenges in the construction process.

[0041] Existing construction methods mainly include chemical vapor deposition (CVD), mechanical exfoliation, and layer-by-layer transfer stacking. Although these methods have their own advantages, they all have certain limitations. Although the CVD method can be used for large-area synthesis, the optical properties (such as fluorescence emission) decrease with the increase in the number of layers due to the band evolution caused by the enhanced interlayer coupling, and it is difficult to accurately control the interlayer angle and stacking order. Although the mechanical exfoliation method can obtain high-quality single-layer materials, its size and morphology are limited, and it is difficult to reuse on a large scale. Although the layer-by-layer stacking method can achieve high-precision interlayer angle control, it requires multiple transfer operations, resulting in low preparation efficiency, and may introduce problems such as interface contamination and stress accumulation, affecting the stability and optoelectronic properties of the multilayer crystal.

[0042] In view of the limitations of the prior art, the present invention provides a three-dimensional crystal construction method based on exponential growth, which optimizes the stacking method to achieve the preparation of high-quality multilayer crystals in a more efficient and controllable manner. The core idea of ​​the present invention is to cut the two-dimensional material elementary structure and stack it using its own physical properties, so that the number of layers increases exponentially within a limited number of operation steps. This method can not only reduce the number of operations required for the traditional layer-by-layer stacking method and improve the preparation efficiency, but also ensure that all layers are derived from the same parent material, avoiding the lattice mismatch problem that may occur when materials from different sources are stacked. In addition, the method of the present invention can achieve accurate replication of the stacking angle between layers, ensure the consistency of the interlayer coupling state, and thus optimize the optical and electronic properties of the multilayer crystal.

[0043] Please refer to Figure 1 and Figure 2 As shown, the method for constructing a three-dimensional crystal in one embodiment of the present invention specifically includes the following steps:

[0044] S101: Provide a two-dimensional material elementary structure with m layers.

[0045] Step S101 is intended to provide a two-dimensional material elementary structure with m layers as the starting point of the entire construction process. This layer can be a single layer (m=1) or a multilayer (m>1) of two-dimensional material, such as transition metal chalcogenides (TMDCs, such as MoS 2 ,WSe 2 ), graphene or hexagonal boron nitride, etc.

[0046] Viable preparation schemes include mechanical exfoliation, which uses tape to peel off thin layers from bulk materials. This is simple and direct, and can retain the high-quality crystal structure of the material; or chemical vapor deposition (CVD) is used to grow two-dimensional materials with a specific number of layers on a substrate, which is suitable for large-scale preparation; in addition, physical vapor deposition (PVD) is also an option, which can precisely control the initial number of layers through evaporation or sputtering deposition. The role of this step is to provide flexible starting materials for subsequent operations. The choice of m value determines the number of layers of the final crystal, and the compatibility of multiple preparation schemes ensures the adaptability of the method to different materials and application scenarios.

[0047] A variety of preparation methods (PVD, CVD, exfoliation) can be used to provide a rich selection of materials, whether it is single-layer TMDCs (such as WSe 2 ), multilayer homogeneous structures, or prefabricated heterogeneous structures (such as MoS 2 / WSe 2 superlattice) can be used as the starting material.

[0048] In an exemplary embodiment, the two-dimensional material elementary structure obtained by physical vapor deposition, chemical vapor deposition or stripping method can be transferred to a flexible polymer. The choice of flexible polymer is usually based on PDMS, because of its good elasticity and adhesion, which is convenient for subsequent operations, but other flexible materials such as polyimide (PI), polymethyl methacrylate (PMMA), polycarbonate (PPC), polyvinyl alcohol (PVA) or polyethylene terephthalate (PET) can also be used as needed. The substrate includes a substrate layer and a sacrificial layer formed on the surface of the substrate layer, and the material of the substrate layer is SiO 2 / Si, gold, sapphire, quartz or boron nitride, and the material of the sacrificial layer is nickel, iron, copper, aluminum, zinc, titanium, molybdenum or chromium.

[0049] S102: Cutting the two-dimensional material elementary structure into a first part and a second part.

[0050] In the process of building a three-dimensional crystal, the goal of step S102 is to split the initial two-dimensional material elementary structure into two parts so that they can be stacked in the subsequent steps to double the number of layers. This process achieves the transition from a single matrix to a multi-layer structure by dividing the initial material into two independent but identical units.

[0051] The specific method for implementing step S102 can be designed according to the process requirements and material properties. A feasible implementation scheme is to use the mechanical separation technology of the substrate edge. The two-dimensional material elementary structure transferred to the flexible polymer (such as PDMS) in step S101 is placed on a hard substrate with sharp edges (such as Ni / SiO2 / Si substrate), so that part of the material is attached to the hard substrate and the other part remains suspended. Subsequently, by applying a slight shear force or tension, the material is divided into two by the cutting effect of the edge. For example, the PDMS can be slowly moved by a precision translation stage to break the material along the edge, forming a first part attached to the hard substrate and a second part remaining on the PDMS.

[0052] Another feasible solution is to use micromachining technology, such as using a focused ion beam (FIB) or laser cutting equipment to accurately define the boundary line on the two-dimensional material element structure and achieve cutting through local energy input. In addition, ultrasonic-assisted cutting is also a feasible method, which breaks the material at a predetermined position by applying ultrasonic vibrations in a liquid environment. Among these methods, mechanical separation is more commonly used due to its simplicity and low equipment requirements, while micromachining technology is suitable for scenarios that require high precision.

[0053] In an exemplary embodiment, step S102 specifically includes: making a part of the two-dimensional material element structure on the flexible polymer adhere to the substrate, and keeping the other part suspended; applying force to the two-dimensional material element structure along the edge of the substrate to cut the two-dimensional material element structure into a first part and a second part, wherein the first part is adhered to the substrate and the second part is adhered to the flexible polymer.

[0054] Specifically, the two-dimensional material primitive structure is first transferred to a flexible polymer (such as PDMS) and uniform adhesion is ensured between the material and the PDMS. Next, the PDMS carrier is slowly moved so that part of the material layer contacts and adheres to the rigid substrate (such as Ni / SiO 2 / Si composite substrate), while the other part remains suspended. 2 The bonding force between the Si / Si composite substrate and the two-dimensional material elementary structure is usually stronger than the bonding force between PDMS and the material layer. When appropriate external force is applied to the material layer, the material will naturally cut along the edge of the substrate.

[0055] In the specific implementation process, the sharp edge of the substrate can be used as a fulcrum for cutting. When the PDMS moves slowly, the edge of the substrate exerts local stress on the two-dimensional material elementary structure, causing the material to separate preferentially along the substrate boundary. Part of the material is firmly attached to the substrate, while the other part remains on the PDMS, thereby completing the cutting operation. This method avoids the material damage that may be introduced by traditional mechanical cutting or laser etching. At the same time, since the entire process occurs at room temperature, no additional thermal stress or chemical contamination is introduced, making the final multilayer crystal structure more uniform.

[0056] Monolayer MoS 2 For example, it is assumed that it has been transferred to PDMS in step S101. In the specific implementation, the MoS 2 Ni / SiO 2 The sharp edge of the Si substrate makes half of the MoS 2 In contact with the Ni surface. 2 The van der Waals force between them is greater than that between PDMS and MoS 2 The adhesion of MoS 2 Break along the edge, the first part is attached to Ni / SiO 2 / Si, and the second part remains on PDMS. The two-dimensional material elementary structure is divided into two parts by physical means, ensuring that both parts inherit the crystal structure and performance of the parent body, providing a unit that can be directly combined for subsequent stacking (S103), thereby achieving multiplication of the number of layers, rather than relying on growth or layer-by-layer addition.

[0057] The binding force between the two-dimensional material elementary structure and the substrate is greater than the binding force between the two-dimensional material elementary structure and the flexible polymer. The difference in binding force mainly comes from the surface energy, chemical interaction and physical adsorption force of different substrate materials. Generally, the binding of flexible polymers (such as PDMS membranes) and two-dimensional material elementary structures mainly relies on van der Waals forces, while rigid substrates (such as Ni / SiO 2 There may be stronger electrostatic interaction, chemical bonding or higher surface energy induced adsorption between the two-dimensional material elementary structure (Si / Si composite substrate). This difference makes the two-dimensional material elementary structure more inclined to adhere to the rigid substrate when appropriate mechanical action is applied, while the part on the flexible substrate is easier to peel off and used for subsequent stacking operations.

[0058] S103: Stack the first part and the second part to double the number of layers of the two-dimensional material elementary structure.

[0059] In the process of constructing three-dimensional crystals, the purpose of step S103 is to stack the first part of the cut two-dimensional material elementary structure with the second part, so as to double the number of layers. In this process, the stacked material layers are physically adsorbed by Van der Waals force to maintain a stable interlayer bonding state. Due to the layered structure characteristics of the two-dimensional material itself, this stacking can naturally form a stable interlayer interaction without the need for additional chemical bonding or high temperature treatment, thereby avoiding interface contamination or stress damage that may be introduced by traditional methods.

[0060] In a specific implementation, the second part of the material retained on the flexible substrate can be translated or rotated by mechanical control or manipulation of the flexible substrate to achieve precise alignment with the first part of the material fixed on the rigid substrate. Since both parts are derived from the same parent material, they are highly consistent in terms of lattice matching, interlayer spacing, etc., thereby ensuring the coupling state between the final stacked layers. In addition, in order to optimize the stacking quality, alignment marks or optical interference-assisted adjustment methods can be used to ensure that the relative position of the two parts remains in the optimal state.

[0061] In an exemplary embodiment, step S103 specifically includes: moving the flexible polymer so that the second part attached to the flexible polymer is stacked with the first part attached to the substrate to obtain a two-dimensional material elementary structure with doubled number of layers.

[0062] The specific implementation method of step S103 can be flexibly designed according to the accuracy requirements and material properties. One feasible solution is to use a transfer platform for precise stacking. For example, in step S102, the first part is attached to a hard substrate (such as Ni / SiO 2 / Si composite substrate), and the second part remains on a flexible polymer (such as PDMS). With the help of a transfer system equipped with a micro-displacement stage and a microscope, the PDMS is moved so that the second part is spatially aligned and in contact with the first part, and the stacking is completed by light pressure or natural fit. During the stacking process, the relative angle of the two parts can be adjusted by rotation, for example, to achieve a zero torsion angle, to optimize the interlayer coupling state.

[0063] Monolayer MoS 2 For example, assuming that step S102 has cut it into Ni / SiO 2 In step S103, the second part of MoS on the PDMS is transferred using a transfer platform. 2 Move it over the first part, observe under a microscope to ensure that the edges of the two parts are aligned, and then slowly lower the PDMS to make the two layers of MoS 2 Contact and fit together to form a double-layer MoS 2 Structure. Since stacking relies only on van der Waals forces, no chemical bond is formed between the first part and the second part, and the weak coupling characteristics are retained. Through the physical stacking of the first part and the second part, the initial number of layers is doubled, while the weak interaction between the layers is maintained, and the optical and electronic properties are optimized through van der Waals coupling.

[0064] In an exemplary embodiment, the construction method also includes: placing the stacked structure comprising a flexible polymer, a two-dimensional material elementary structure and a substrate in a chemical solution, dissolving the bonding interface between the substrate and the two-dimensional material elementary structure, separating the substrate from the two-dimensional material elementary structure, and transferring the two-dimensional material elementary structure to the flexible polymer.

[0065] Specifically, after completing a stacking of multiplied layers, the entire structure usually includes a flexible polymer, a two-dimensional material elementary structure, and a rigid substrate. In order to achieve efficient separation of the two-dimensional material elementary structure, a suitable chemical dissolution method can be selected to remove the bonding interface (sacrificial layer) between the substrate and the material layer. The substrate conversion of the stacked structure is achieved through chemical separation, providing a basis for subsequent repeated operations and final crystal transfer.

[0066] The specific implementation method of the substrate separation step can be flexibly designed according to the characteristics of the substrate material and the chemical solution. One feasible solution is to use an acidic solution to dissolve the metal substrate. For example, the substrate is Ni / SiO 2 / Si, the flexible polymer is PDMS, and the stacked two-dimensional material elementary structure (such as double-layer MoS 2 ) attached to the Ni surface. The entire structure is immersed in a dilute hydrochloric acid solution (such as 0.1 mol / L HCl), and the Ni layer (sacrificial layer) gradually dissolves in the acidic environment, releasing SiO 2The bonding interface between the / Si substrate and the two-dimensional material elementary structure. Subsequently, the PDMS and the two-dimensional material elementary structure were taken out of the solution with tweezers or a transfer tool, washed with ultrapure water to remove the residual acid, and finally dried quickly to make the double-layer MoS 2 Completely transferred to PDMS.

[0067] Another way is to select specific solutions for different substrates, such as using potassium hydroxide (KOH) solution to dissolve aluminum substrates, or using hydrofluoric acid (HF) to etch SiO2 layers, depending on the chemical properties of the substrate. In addition, the separation effect can be optimized by controlling the solution concentration, immersion time (such as 5 to 10 minutes) and temperature (such as room temperature to 40°C) to ensure that the two-dimensional material unit structure is not damaged.

[0068] Double-layer WSe 2 For example, the specific implementation process may be as follows: In step S103, WSe 2 The first part and the second part are stacked to form a double-layer structure, the first part is attached to the Ni / SiO2 / Si substrate, and the second part is transferred from PDMS. 2 and Ni / SiO 2 / Si structure was placed in a dilute hydrochloric acid solution. The Ni layer dissolved within a few minutes and the double-layer WSe 2 Detached from SiO 2 / Si substrate, attached to it due to the adhesion of PDMS. After cleaning and drying, the double-layer WSe 2 Successful transfer to PDMS.

[0069] S104: Repeat steps S102 and S103 at least once, and form m×2 layers through N stacking operations. N A three-dimensional crystal of layers, wherein m and N are positive integers greater than or equal to 1.

[0070] Step S104 repeats the cutting (S102) and stacking (S103) operations, so that the number of layers of the two-dimensional material elementary structure increases exponentially, thereby achieving a leap from the initial two-dimensional material elementary structure to a multi-layer three-dimensional structure.

[0071] Specifically, after completing one slicing and stacking, the initial two-dimensional material primitive structure (m layers) will become 2m layers, and then it can be sliced ​​and stacked again, so that the number of layers continues to double. For example, after the Nth operation, the final three-dimensional crystal layer number can reach m×2 N Taking the simplest single-layer (m=1) initial material as an example, if four cycles are performed (N=4), a 16-layer three-dimensional layered crystal can be obtained in the end, while the traditional layer-by-layer stacking method requires 15 operations to achieve the same number of layers, significantly improving the preparation efficiency.

[0072] Monolayer MoS 2 (m=1) as an example, the specific implementation process may be: Step S101 provides a single layer of MoS 2 and transferred to PDMS, S102 cuts it into the first part (attached to Ni / SiO 2 / Si) and the second part (remaining on PDMS), S103 stacking to form a double-layer MoS 2 Then, S104 is executed. In the first repetition, the double-layer MoS 2 Transfer back to PDMS (as described in the previous chemical dissolution step, Ni can be dissolved by dilute hydrochloric acid), cut into two parts again and stacked to obtain 4 layers of MoS 2 ; The second repetition yields 8 layers, and the third repetition yields 16 layers. If N = 4, a 16-layer three-dimensional crystal is formed by 4 stacking operations.

[0073] The present invention also provides a three-dimensional crystal, which is constructed by the aforementioned construction method. The layers of materials in the three-dimensional crystal are coupled by van der Waals forces, and stable interlayer bonding is achieved through weak interactions between molecules.

[0074] The interlayer spacing of this three-dimensional crystal can be fine-tuned by applying pressure, electric field or twist angle, making it suitable for applications such as high-performance optical components (such as near-infrared lasers and photodetectors) and two-dimensional superconducting systems (such as magic-angle graphene and TMDCs superlattices). 2 / MoS 2 In layered heterojunctions, van der Waals stacking can enhance the binding force of interlayer excitons, thereby improving the photoluminescence efficiency, making it a candidate material for the new generation of quantum light sources.

[0075] The present invention also provides an optical element, which includes the aforementioned three-dimensional crystal. The optical element utilizes the layered stacking characteristics of two-dimensional materials and combines interlayer control technology to optimize photoelectric characteristics such as light absorption, photoluminescence, and carrier transport.

[0076] The present invention will be further described below in conjunction with specific embodiments.

[0077] Example 1: Construction of millimeter-scale 16-layer stepped MoS 2 Crystal

[0078] Using the aforementioned three-dimensional crystal construction method, centimeter-scale single-crystalline MoS grown by CVD 2 (like Figure 3 As shown in the figure, through four "pick-up-press-cut-stack-pick-up" operations, the millimeter-scale 16-layer stepped MoS 2 Crystals (such as Figure 4 and Figure 5 shown).

[0079] Figure 6 The 16-layer stepped MoS with different number of layers in Example 1 2 Photoluminescence spectrum of the crystal. Figure 6 It can be seen that all spectra have two obvious luminescence peaks, corresponding to A excitons and B excitons respectively. The peak positions and peak shapes of the fluorescence spectra are basically the same, and the fluorescence intensity increases with the number of layers.

[0080] Figure 7 The 16-layer stepped MoS in Example 1 2 Crystal and 2H phase MoS 2 Comparison of the photoluminescence properties of the crystals. Figure 7 It can be seen that the 2H phase MoS prepared by mechanical exfoliation 2 The fluorescence intensity of the crystal decreases with the increase of the number of layers. Since the single-layer sources of the two crystals are different but the basic optical properties are the same, for the convenience of comparison, the single-layer fluorescence spectra of the two crystals are normalized, and the corresponding multi-layer crystals are multiplied by the same coefficient as the single layer. After comparison, it is found that the millimeter-scale 16-layer stepped MoS 2 The A exciton fluorescence intensity of the crystal is 2H phase MoS obtained by mechanical exfoliation. 2 The fluorescence intensity of the crystal is 300 times that of the original.

[0081] To make the comparison more intuitive, the CVD-grown and mechanically exfoliated single-layer MoS 2 The fluorescence intensity of the crystals was normalized and then the fluorescence intensity of the multi-layer crystals was processed proportionally. Figure 8 As shown, Figure 8 a and Figure 8 b are millimeter-scale 16-layer stepped MoS 2 Optical microscopic images and fluorescence spectral imaging of the crystal show that within the millimeter-scale range, the fluorescence imaging of regions with different numbers of layers is relatively uniform. Some of the inhomogeneities may come from the single-layer CVD-grown single crystal MoS 2 As well as defects generated during the transfer process, the single-layer area also has some unevenness at the millimeter scale. In the future, based on improving the wafer-scale MoS 2 The sample quality of single crystals can be avoided by further optimizing the transfer and fabrication processes. In addition, with the increase of the number of layers, MoS 2 The fluorescence emission intensity of the crystal shows a monotonically increasing trend. The difference is that Figure 8 c and Figure 8 d are 2H phase MoS 2 Optical microscopic images and fluorescence spectral imaging of the crystal, in which the fluorescence emission intensity in the single-layer area is the highest, and the fluorescence emission intensity decreases sharply with the increase in the number of layers.

[0082] The 16-layer stepped MoS 2 Crystal and 2H phase MoS 2 The integrated fluorescence intensity at the A exciton energy, which depends on the number of layers of the crystal, is counted, and the single layer is used as the benchmark for normalization, such as Fig. 9 As shown, 16-layer stepped MoS 2 The integrated fluorescence intensity of the crystal increases with the number of layers and gradually tends to saturation, and the change pattern with the number of layers is similar to the change pattern of the absorption intensity with the number of layers. By dividing the integrated fluorescence emission intensity with the absorption intensity and taking the single layer as the normalized benchmark, the 16-layer stepped MoS 2 The relative quantum yield of the crystal, such as Fig.10 As shown, compared with single-layer MoS 2 The QY of the crystals is basically similar, which further demonstrates its excellent monolayer-like luminescence properties.

[0083] Example 2: Construction of 8-layer WSe 2 / MoS 2 Superlattice

[0084] Using the aforementioned three-dimensional crystal construction method, from the double-layer WSe 2 / MoS 2 Heterogeneous superlattice (such as Fig.11 As shown in the figure, through two "pick-up-press-cut-pick-up" operations, 8 layers of WSe are obtained by cyclic stacking. 2 / (MoS 2 / WSe 2 ) 3 / MoS 2 Superlattice (such as Fig.12 and Fig.13 shown).

[0085] Fig.14 For the 8-layer WSe in Example 2 2 / (MoS 2 / WSe 2 ) 3 / MoS 2 Schematic diagram of the exciton types (including intralayer excitons, dipole interlayer excitons and quadrupole interlayer excitons) of the heterogeneous superlattice. Fig.15 For the 8-layer WSe in Example 2 2 / (MoS 2 / WSe 2 ) 3 / MoS 2 Heterogeneous superlattice and double-layer WSe 2 / MoS 2 Near-infrared fluorescence spectrum of heterojunction. Fig.14 and Fig.15It can be seen that 8 layers of WSe 2 / (MoS 2 / WSe 2 ) 3 / MoS 2 The emission intensity of interlayer excitons (IXs) in the near-infrared II region (NIR-II) of the superlattice is higher than that of bilayer WSe. 2 / MoS 2 The dipole moment of the superlattice increases the intensity of interlayer exciton emission by four times, indicating that the interlayer exciton luminescence in the heterogeneous superlattice will be significantly enhanced with the increase of the number of layers, but this needs to be based on the premise of a unified interlayer coupling state. 2 / (MoS 2 / WSe 2 ) 3 / MoS 2 The superlattice further verified the superiority of the construction method of the present invention, which can improve the optical properties of heterogeneous superlattices and provide a basis for the subsequent exploration of the layer-number-dependent optical properties of heterogeneous superlattices and the development of near-infrared optical elements.

[0086] In summary, the three-dimensional crystal, its construction method, and optical element provided by the present invention cut the two-dimensional material elementary structure and stack it using its own physical properties, so that the number of layers increases exponentially within a limited number of operation steps; this method can not only reduce the number of operations required for the traditional layer-by-layer stacking method and improve the preparation efficiency, but also ensure that all layers are derived from the same parent material, avoiding the lattice mismatch problem that may occur when materials from different sources are stacked.

[0087] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0088] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for constructing a three-dimensional crystal, characterized in that: The following steps are involved: S101: providing a two-dimensional material elementary structure having m layers; S102: cutting the two-dimensional material elementary structure into a first part and a second part; S103: stacking the first part and the second part to double the number of layers of the two-dimensional material elementary structure; S104: Repeat steps S102 and S103 at least once, and form m×2 layers through N stacking operations. N A three-dimensional crystal of layers, wherein m and N are positive integers greater than or equal to 1.

2. The method for constructing a three-dimensional crystal according to claim 1, characterized in that: Step S101 specifically includes: The two-dimensional material elementary structure obtained by physical vapor deposition, chemical vapor deposition or exfoliation method is transferred to a flexible polymer.

3. The method for constructing a three-dimensional crystal according to claim 2, characterized in that: Step S102 specifically includes: A part of the two-dimensional material elementary structure on the flexible polymer is attached to the substrate, and another part is kept suspended; A force is applied to the two-dimensional material elementary structure along the edge of the substrate, so that the two-dimensional material elementary structure is cut into a first part and a second part, wherein the first part is attached to the substrate, and the second part is attached to the flexible polymer.

4. The method for constructing a three-dimensional crystal according to claim 3, characterized in that: The bonding force between the two-dimensional material elementary structure and the substrate is greater than the bonding force between the two-dimensional material elementary structure and the flexible polymer.

5. The method for constructing a three-dimensional crystal according to claim 4, characterized in that: The flexible polymer is PDMS, PMMA, PPC, PVA, PI or PET film, the substrate includes a base material layer and a sacrificial layer formed on the surface of the base material layer, the base material layer is made of SiO2 / Si, gold, sapphire, quartz, or boron nitride, and the sacrificial layer is made of nickel, iron, copper, aluminum, zinc, titanium, molybdenum or chromium.

6. The method for constructing a three-dimensional crystal according to claim 3, characterized in that: Step S103 specifically includes: The flexible polymer is moved so that the second part attached to the flexible polymer is stacked with the first part attached to the substrate, thereby obtaining a two-dimensional material elementary structure with doubled number of layers.

7. The method for constructing a three-dimensional crystal according to claim 6, characterized in that: The construction method also includes: The stacked structure including the flexible polymer, the two-dimensional material elementary structure and the substrate is placed in a chemical solution to dissolve the bonding interface between the substrate and the two-dimensional material elementary structure, so as to separate the substrate from the two-dimensional material elementary structure and transfer the two-dimensional material elementary structure to the flexible polymer.

8. The method for constructing a three-dimensional crystal according to claim 1, characterized in that: The two-dimensional material elementary structure is a single-layer two-dimensional material or a multi-layer heterogeneous two-dimensional material, and the material of the two-dimensional material elementary structure is a transition metal chalcogenide, graphene or hexagonal boron nitride.

9. A three-dimensional crystal, characterized in that: The three-dimensional crystal is constructed by the construction method according to any one of claims 1 to 8, and the layers of materials in the three-dimensional crystal are coupled by van der Waals forces.

10. An optical element, characterized in that: Comprising the three-dimensional crystal as described in claim 9.

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